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ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.1.1 Identification | − Mr, Mrs, Ms − surname − given name − photo − etc. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.1.2 Geographical localization | − postal address − physical address − site − room number − building − etc. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.1.3 Organizational affiliation | − company − organizational unit − division − function − speciality, activity, competence area TR 101 153-2 V1.1.1 (1998-01) 12 − hierarchical position − direct senior officer − etc. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.1.4 Communication means | − fixed phone − mobile phone − fax − e-mail address − secretariat − pager − switch board attendant − etc. The above elements have been proposed as a basis for standardization by ETSI of the content in order to allow information interchange tools to work between the different information sources. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.2 Data interchange | Since there is a clear need for consolidation or synchronization of information between different sources, relevant interfaces have to be designed and implemented. This is true for corporate directories as well as for personal customized directories. Some additional information may be found at http://www.ema.org/html/at_work/dirsync.htm [13]. The standardization of these interfaces has been proposed for inclusion in the ETSI Work Programme. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.3 Security aspects | Since there are understandable reservations about making public any information in a private directory, tools are needed to restrict access to the accredited persons only, according to the type of information concerned. Similarly, if encryption keys for secured transactions are to be stored in a directory system, access and management of these parameters should obviously be restricted to authorized personel. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.4 Data management | Although there is a need for a corporate directory system manager, information updating should more and more be dealt with in a decentralized way. Therefore, tools should be implemented to manage which parts of the database are allowed to be updated by each local manager. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 5.5 Search tools, editing and downloading facilities | Sophisticated means are required by the end-users to allow them to find someone not only starting from the approximate spelling of the name but also from quite different criteria like function, professional skills, etc. Editing and downloading facilities are also required to enable printing and data extraction according to end-user criteria and in order to prepare a private directory on paper. TR 101 153-2 V1.1.1 (1998-01) 13 |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6 Corporate naming and directory schema | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.1 Introduction | When establishing a corporate directory service, there are many aspects to be considered. This clause considers the following aspects: - unambiguously naming all items or objects to be represented in a directory; and - how information is structured. The above aspects are part of what is referred to as the directory schema. Some tutorial material on directory schema definitions can be found in subclause 6.4 "Directory schema". It is assumed here that a directory is either based on the X.500 technology or at least complies with the specifications described in subclauses 6.3 and 6.5 necessary to ensure interoperability. It is also assumed that the reader has a basic knowledge of this technology. However, it has been attempted to keep the technical details down to a minimum level. It is important to remember that each object represented in an X.500 directory is represented by an entry in the directory and that the entries are placed in a so-called Directory Information Tree (DIT) where the placement of the entry is determined by the object's (or entry's) name. A few notes on directory schema are presented in the following subclauses. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.2 Understanding the directory environment | PRDMD1 PRDMD2 PRDMD3 ADDMDa ADDMDb C O C L O O Root Figure 1: Scope of a corporate directory This section describes the scope of a corporate directory with respect to a more general directory infrastructure, e.g. a pan-European Directory. This is illustrated in figure 1, where a number of Administrative Directory Management Domains (ADDMDs) and Private Directory Management Domains (PRDMDs) are shown. In this simple figure the PRDMDs represent the corporate directories, while the ADDMDs are public service provider directories. The ADDMDs have the responsibility for establishing a wider directory infrastructure and for holding the country entry, while the top entry in a PRDMD has the organization entry as the top of its tree (subtree). It should be understood that this is quite a simplified picture. There may be several ADDMDs in a single country each wanting to hold the country entry. This introduces a number of issues, which can be more or less ignored by a corporate directory (PRDMD) and therefore are out of scope of the present document. Likewise, ADDMDs are faced with other particular issues for their interoperation, which are also outside the scope of the present document. TR 101 153-2 V1.1.1 (1998-01) 14 The scope of the corporate directory as treated in the present document represents the situation where a corporate directory is either an isolated directory not connected to any general infrastructure, or if it is connected, it is subordinate to some ADDMD. Thereby, it is shielded from the particular ADDMD problems. Connecting to a wider infrastructure will allow information provided by the corporate directory to be accessed from the outside, and it will allow corporate users to access information outside the corporate directory, e.g. information in another corporate directory or in a public directory. Even if a corporate directory is initially an isolated directory, it should be part of the planning that it may at some later time be connected to a wider directory infrastructure. An international organization has additional issues to consider when establishing an international corporate directory. Such issues are examined in subclause 6.6 "International organizations". |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.3 Objects in a directory | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.3.1 Object classes and attribute types | As explained in subclause 6.4 "Directory schema", an entry is created based on an object class specification determining the characteristics of the entry. An organization therefore has to decide what object classes to use for the different entries. An object class specification also determines what attribute types can be represented in an entry, i.e. it determines what kind of information can be stored in the entry in question. The base X.500 standard defines several object classes and attribute types (see ITU-T Recommendation X.520 | ISO/IEC 9594-6 >6@ and ITU-T Recommendation X.521 | ISO/IEC 9594-7 >7@). These object classes and attribute types should first be considered and used whenever possible. If they do not fulfil reasonable requirements other generally used schema elements should be used. The EWOS Web-pages [12] point to such general used schema definitions. When deciding what object classes to use for entries in a corporate directory, it is important to know the concepts of structural object class, subclass and auxiliary object class. Tutorial material on these issues is also available on the EWOS Web pages [12]. The following subclauses further consider this issue. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.3.1.1 Organizational persons | When creating entries for organizational persons there are several different object classes that can be considered: - The X.500 standard defines an object class for persons in general from which the two basic object subclasses for persons, one for residential persons and one for organizational persons (organizationalPerson), are derived. The organizational person object class has some limitations with respect to allowable attribute types. When this object class is used, it will in most cases have to be supplemented with one or more auxiliary object classes. - ITU-T Recommendation X.402 | ISO/IEC 10021-2 [12] defines an auxiliary object class called mhs-user which, when combined with a structural object class like organizationalPerson, allows inclusion of X.400 relevant attribute types. - The Internet specification RFC-1274 [14] specifies a number of schema elements that are widely used, e.g. in the NameFLOW-paradise project. This RFC defines a structural object class (pilotPerson object class) that can contain quite a lot of useful attributes. However, it is most useful in the academic society. - The European International Directory Inquiry (EIDQ) activity, which is making schema specifications mostly for the telephone numbering service, is also defining its own person object classes. It has defined a fdasResPer, which allows inclusion of several generally usable attributes, but also some that are quite EIDQ specific. The EIDQ specifications cannot be considered stable at the present time. - An organization could define its own object class either as an auxiliary object class that can supplement some other person related object class, or it can define a complete replacement structural objects class. Defining one's own object classes should be absolutely the last choice. TR 101 153-2 V1.1.1 (1998-01) 15 - EWOS/EG DIR has defined an auxiliary object class. This auxiliary object class allows inclusion of all attribute types which have been judged useful. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.3.2 Representation of roles | An organization may want to make a distinction between a person as an individual and as a person performing a particular role. Likewise, a user accessing the directory may at some time want information about a particular individual and at other times want information on a particular function within the organization, e.g. the person responsible for education. A particular person may at a certain time be represented by more than one entry where only one of those is the person’s individual entry. The person "behind" a functional entry may change over time, but the entry itself is maintained. If the same person is performing a particular function over a longer period, pointers can be established between the person's personal entry and the functional entry. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.4 Directory schema | For directory information to be usable and accessible, it has to be organized in a pre-defined way. The rules for how directory information is organized is called the directory schema. The directory schema is made up of several elements: - Object classes are specifications of the characteristics or an object of a particular type, e.g. a residential person, and therefore determine the contents and other features of the entry representing such an object. - The entry information is stored as a number of attributes each representing a particular piece of information. The characteristics of an attribute are determined by an attribute type definition, which is a specification of its structure and syntax. The syntax can be quite simple or be rather complex. - When interrogating entry information, it is in many cases necessary to compare the value of an attribute with some data element presented in the user request. This is the case for searches where entries are selected based upon whether they fulfil certain criteria. The rules for how such a comparison shall be made are called matching rules. Matching rules can be quite simple like an exact match between two integers, or they can be rather complex, like a word rotation matching rule, phonetic matching rule and other approximate matching rules. While commonly recognized matching rules are implemented in all X.500 products, more special matching rules require special implementation. - An entry's placement within the Directory Information Tree (DIT) and its name structure is determined by a structure rule. All the above schema elements, and a few more, determine the characteristics of an entry and its relation to other entries. For a Directory System Agent (DSA), i.e. a directory server, to contain a particular entry it is necessary for the DSA to have implemented all the schema elements that govern the characteristics of that entry. For a Directory User Agent (DUA), i.e. a directory client, to access this entry and utilize the stored information, it also needs to have a pretty good understanding of all the schema elements. If users through their DUAs access different directory domains, they would expect the same type of information, like an e-mail address, to be controlled by the same schema element independent of location, otherwise the DUA may not be able to utilize the information. If all organizations, like the Internet, private organizations, national groups, etc., each independently make their own directory schema definitions, which is somewhat the case today, it will not be possible to make a truly integrated European directory. Even though it may be possible to physically interconnect different domains, they will not be able to utilize each other's information. TR 101 153-2 V1.1.1 (1998-01) 16 |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5 Naming aspects | The X.500 Directory standard requires every object (person, organization, etc.) which is to be represented in a directory to be unambiguously named. A directory name is composed of a number of name components forming a hierarchical structure. Typically, the first component is a country code, the next a locality name, the next again the company name, and so on. Naming is probably one of the more difficult aspects to consider when establishing a corporate directory. C=XX O=Tiny L=Small Area O=Biggy Figure 2: Location of main entry for organization Account should be taken of the fact that the corporate directory might, in the future, connect into a wider directory infrastructure, e.g. a national or a European structure. It should be checked whether there are some national recommendations on how organizations should be named in a wider directory context. A large corporation will probably have its main entry located right under the country entry, while a smaller organization might have its entry under an entry representing a smaller area, like a postal district. This is illustrated in figure 2. The large organization to the left has its entry just below the country entry and the name of the main entry is then: { C=XX; O=Biggy }. The organization to the right is a smaller organization represented by an entry having the somewhat longer name: { C=XX; L=Small Area; O=Tiny }. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5.1 Corporate subtree | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5.1.1 General considerations | O=xyz OU=def OU=abc OU=ghi OU=klm OU=opq OP1 OP4 OP3 OP1 OP2 OP3 OP1 OP2 OP3 Deep subtree Shallow subtree O=xyz OP1 OP2 OP3 OP4 OP5 OP6 OP7 OP8 OP9 Figure 3: Deep and shallow subtrees Selecting a naming structure is one of the more crucial choices to be made by an organization when setting up a corporate directory. The choice of naming structure influences the usefulness of the directory, and it affects how the directory can be maintained. The organization's naming tree forms a subtree of a more global Directory Information Tree (DIT), where the organization entry is the root of that subtree as illustrated in figure 1 and as explained in the associated text. An organization can select to make its subtree deep or shallow. Figure 3 illustrates the extremes of these two approaches. TR 101 153-2 V1.1.1 (1998-01) 17 The left side illustrates the situation where the naming structure, and thereby the information structure, reflects the structure of the organization. The naming structure will then have levels corresponding to the organization hierarchy. The right hand side of the figure shows the other extreme where the naming structure has only a single level below the organization entry. The two approaches have both advantages and disadvantages. In each particular situation some combination or some in-between solution may be selected, taking into consideration that each approach has advantages and drawbacks. Next are some considerations on how the two approaches can be combined to cope with different situations. The deep subtree has the following advantages compared to the shallow subtree: − Reduced number of nodes per level: − Anything else equal to any particular entry, e.g. an organizational unit entry, will have fewer subordinate entries in a deep tree than in a shallow tree. This makes it easier to ensure unique naming, as name components (Relative Distinguished Names) only have to be unique with respect to the superior entry. In the shallow tree there is a larger likelihood of collapse of names. Names or identifiers, e.g. initials, may only be unique within a single department. − Support of registration: − This advantage is related to the previous one. The process of establishing unique names or identifiers for persons and functions can be distributed within the organization. This advantage is of course dependent on whether there are organization-wide unique identifiers of employees in place. In many organizations each employee is given a unique identifier, most often based on initials for other purposes, such as log-on identifier on the local Information Technology system. − To achieve geographical or organizational subdivision: − Large corporations may be dispersed in two ways: − geographically dispersed, where each location has some autonomy, e.g. own personnel department, employee policy, etc.. − have very different objectives in the form of services provided, products, customers, etc.. In such organizations it will probably be a requirement to have separate subtrees for such dispersed units: − To express ownership of part of the DIT: − Particularly in large organizations it may be a requirement that a certain department can claim ownership of its part of the DIT. This is not easily achieved if the departmental entries do not form a subtree of its own. − Partitioning into administrative areas: − Different parts of the corporation may require to manage their own parts of the corporate subtree. This may be a requirement even in the case where the department does not have a DSA of its own. This will in any case require that the department needs to be represented by a subtree of its own. − Shared information: − A set of entries may share some common information, e.g. a number of a fax machine serving several people. The X.500 standard has feature for supporting that, but that is most easily established if the entries sharing some piece of information form a subtree of their own. − Access control: − Access control capabilities have to be specified with respect to entries to be accessed and with respect to users accessing these entries. Access control specifications are easier to make and maintain if the entries having the same access restrictions form a separate subtree and if the users (or their entries) whose access rights have to be specified also form a subtree. TR 101 153-2 V1.1.1 (1998-01) 18 − Localise a service to part of the DIT: − It may be convenient to have the entries representing a particular service, e.g. the Electronic Data Processing (EDP) department, in a separate subtree. − Distribution of subtrees into different DSAs: − Distributing a corporate directory across several DSAs is more easily accomplished and managed if the part of the subtree to be put into a particular DSA is itself a subtree. − Starting points for searching and browsing: − A corporate wide search for a particular entry may be resource demanding, especially if the corporate directory is distributed across several DSAs. By having a deep subtree, it is possible to start the search somewhere down in the subtree, thereby restricting the search to only a part of the corporate directory. − To document the organization. The shallow tree has different advantages: − The organization can change without changing names: − A subtree that reflects the organization will have to be changed when the organization changes. All names of objects represented by entries are then changed at the same time. The need to be rebuild the directory may be a major undertaking, depending on the administrative tools available. This one aspect may be so important that it outweighs many of the advantages of a deep subtree. − Short names: − A shallow tree gives shorter names. This may be an advantage in some circumstances. Whether the deepness of a subtree affects search performance is implementation dependent. A shallow subtree does not necessarily give a better search performance than a deep subtree or vice versa. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5.1.2 Naming recommendations | Based on the above general considerations it is possible to make some recommendations on the allocation of names. Distinguished names (i.e. the complete name starting from the root down to the object in question) are used to reference objects in many places. It is therefore important that names that are referenced in this way be stable over time. Examples of where distinguished names are used are listed in the following: − Aliases: − An alias entry is an entry pointing to another entry thereby giving an alternative (alias) name for an object. The pointer is the distinguished name of the entry to which it points. − Other types of pointers: − Some attributes are pointers to other entries. For example, the seeAlso attribute points to one or more other entries using the distinguished names of those entries. − List of names: − It is possible to establish a list of names. Such names are distinguished names of other objects, normally persons. Dependent on to what degree such pointer information is established in a corporate directory, it is evident that frequent changes of distinguished names result in a heavy administrative burden and a high risk of inconsistency in the directory. It is therefore essential to limit the changes of distinguished name with organizational changes to a minimum. TR 101 153-2 V1.1.1 (1998-01) 19 When establishing a DSA it has to be determined what the naming prefix is for the entries in the DSA, i.e. what are the top entries from the root down to the organization entry and how are they named. This requires the organization name to be properly registered by an external registration authority and it requires that, within the country, is established an overall structure for the top part of the country subtree. If such information cannot be established from the beginning and arbitrary choices have to be made, later changes may require considerable administrative effort (for selection of organization Relative Distinguished Name (RDN) see subclause 6.5.2.1 "Organization names"). |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5.2 Allocating names | Directory names have to be unambiguous, i.e. there may not be two objects having the same name. At each level of the corporate subtree uniqueness in naming has to be achieved. Allocating name components (RDNs) for different entries in the corporate subtree is not that difficult for objects where the naming is completely under the organization's control and where feelings are likely to be less emotional, such as names for organizational units, organization functions, e.g. accounting, servers, printers, etc. It is more difficult for the top of the subtree, i.e. the organization entry, and for the bottom of the subtree, where persons are to be named. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5.2.1 Organization names | The organizational entry is here assumed to be the top entry of the corporate subtree. Allocating a name for this entry is of course no problem if the corporate directory is never to be connected into a wider directory infrastructure, but such an assumption should not be made. As discussed at the start of clause 6, the organizational entry in a wider directory infrastructure will typically be subordinate to an entry representing some geographical area, either the whole country or a smaller area. The organization name needs to be unique within that area, which requires some kind of external registration authority. If such an authority is not in place for the particular area, there is a risk that the a selected name for the organization may not be unique. In such a situation the organization could consider using a protected name, if the organization name has one. As an example McDonnell would probably consider its name protected, and will sue any other company using that name. An organization could also consider using its Internet domain name, if it has one. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.5.2.2 Naming persons | Persons are normally quite particular about their names, so giving names (RDNs) to persons can be a difficult task. Assigning unambiguous names to residential persons is especially difficult, but this is outside the scope of the present document. However, assigning names to persons in an organization also requires careful consideration. Some personal names are quite common. Even within a somewhat small organization it is not unlikely that several people have the same name. By selecting a deep corporate subtree the likelihood of two persons having the same personal name in a small organizational unit can be made considerably smaller, but it is not zero and will have to be planned for by either attaching additional characteristics information to the personal name to make it unique, or by using a unique person identifier instead. The first thing to consider is whether a person's full name should be used or some other unique person identification. When assigning an RDN it is also necessary to define what attribute type(s) should be used as naming attributes. The X.500 standard defines a name form for organizational persons. This name form specifies that an attribute called commonName should be used as naming attribute. This name form also allows the commonName to be qualified by an organizational unit name, i.e. the RDN may consist of a combination of a common name component and an organizational unit name component. This may achieve unambiguous identification. ECMA TC32 TG13 is also working on this issue and may provide some additional guidance on personal naming. Organizations quite often assign unique identifiers to their employees. For smaller companies it may be a three character identifier (ID), whilst for larger organization more characters may be used. Such unique identifiers are used for log-on IDs, e-mailbox IDs, etc. Using such identifiers has the advantage that no additional naming registration is necessary. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.6 International organizations | International organizations may have a directory system which encompasses several countries world-wide; therefore they need a harmonized naming policy between the related countries and thus an international, and not only European, registration authority for such naming. TR 101 153-2 V1.1.1 (1998-01) 20 |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 6.7 Islands of directories | Private enterprises and public institutions are deploying private directory systems to satisfy internal needs. Such private directories contain information that can be relevant to provide to the outside world, such as telephone numbers for individual employees, job responsibilities, etc. On the other hand, users of a private directory may require access to information available in the global European directory. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7 Data interchange, synchronization, gateways | This text is based upon the following assumptions: - the technical solution for data interchange, synchronization and gateways is based upon X.500 concepts; - the directory (whether centralized or distributed) has its own database, fed by different sources. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1 Identification of interfaces and gateways needed | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.1 Between the directory server and providers of information | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.1.1 Inside the company | − the corporate database (staff data, etc.) − e-mail directory − PBX and telephone lists − practical local information on the life of the enterprise (meeting rooms, medical services, internal mail circuits,...) These are the different sources available to feed the corporate directory, first to initiate the population of the directory and then to regularly update it. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.1.2 Outside the company | − Public directory services − Other corporation directory services − Internet − Public registering systems (Name, Address, VAT, etc.) |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.2 Between the Directory Server and Clients | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.2.1 Inside the company | − e-mail − telephone lists and systems − groupware applications (e.g. Lotus Notes) − security applications TR 101 153-2 V1.1.1 (1998-01) 21 − access control system − paper extraction − LAN, network resources directories (e.g. Novell NDS) |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.2.2 Outside the company | − teleworkers − customers − suppliers − company's partners and subsidiaries |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.1.3 General scheme for information interchange | Figure 4 gives a general picture of the possible data interchanges between the different systems with some indication of the content of information exchanges, taking a corporate directory as an example. In this figure, the corporate directory system may or may not be centralized. This means that, if a decentralized solution is chosen, then the corporate directory system is made up of a network of several local servers with or without local replication of the entire database. In any case, the information is circulated between these local servers and possibly a corporate server. Corporate Directory System Outside the company Public Directory Servers INTERNET Public registering systems: VAT, .. Extended company business dependent organization Customers Partners Teleworkers Corporation borderline - Human Resources - business organisation - shareholding - locations & buildings E mail system PBX, LAN's & WAN's architecture Company internal information system Groupware Applications Security Applications Network Management Customer care & Telemarketing Publishing Name registering systems Address registering system Company core organisation Suppliers Stable manpower & locations kernel Business dependent - organisation - business codes - workgroups - access codes Partners, etc .. directories Directory Providers Call Centres & Help Desks Outsourcers Other Directory systems Other Corporate Directory Servers Distributors & retailers SME's & SOHO's Figure 4: Information Input towards the Corporate Directory System TR 101 153-2 V1.1.1 (1998-01) 22 Table 1: Some indications on the possible content of information exchanges Piece of information From Inside the company From Outside the company To Name, identifier Corporate database (for ex. accounting) The company directory server(s) e-mail address e-mail System Internet or dedicated servers The company directory server(s) Phone number PBX Public directory services, other private directory servers The company directory server(s) Network address Network management Internet The company directory server(s) Local information Company local information systems The company directory server(s) Updates Any company directory server Any other directory server in the company Every "public" piece of information The company directory server(s) Public directory services, other private directory servers, any user |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.2 Objectives | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.2.1 Functional | Most of the applications listed in subclause 7.1 are based on their own directories, which may be outdated, encumbered with information about persons that have left the company, or who were transferred from one organizational unit to another. To all these clients, the corporate directory can provide periodic information on the presence of a person within an organizational unit so that they can update their own information. All updating efforts may then be made only on the corporate directory, which then propagates the changes to its clients. The update is most likely to be decentralized, with the exception of the smallest organizations. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.2.2 Technical | Formats and syntax have to be defined to allow easy data interchange between the different sources and clients. Technical solutions exist, the issue is to agree on which one should be adopted and possibly standardized. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.2.3 Organizational | Related to naming, it may be difficult to find the right « key » to reach the right entry when synchronizing with a source of information. The couple « Surname-GivenName » may not be sufficient, and an unambiguous identifier may be necessary. This aspect is more organizational than technical. More details are given in subclause 6.5. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.3 Solutions | − Synchronization products: most of the directory server products provide synchronization tools that allow to import flat files (CSV type); − « dap » or « ldap » connections; − APIs: these enable existing applications to sit directly on X.500. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 7.4 Open Issues | A common identifier allowing synchronization of information between directories in different companies and with public directories is still to be defined and it has therefore been proposed that this issue be included in ETSI work programme. TR 101 153-2 V1.1.1 (1998-01) 23 |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8 Links with End-user | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.1 Introduction | End-users are interested in electronic directory systems because they expect to find there up-to-date information which might help them to locate the right person to communicate with. To do that, they need to process the information delivered by the directory system, adding their own elements of information to make it relevant. Therefore, they need not only to get information from the system in the right shape but they require also that this information might be updated from the original database when there is a change, without losing the pieces of information they have added in their own database, each user having specific interests and needs. The latter may be stored either in the directory server or in the end-user's terminal. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.2 Objectives, Requirements | Users often prefer looking for a person by using their own criteria even if this lowers system performance. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.2.1 Search tools | When the name of the wanted person is not exactly known, nor his address, nor to which part of a structure they belong, the following features are required for quick identification: - incomplete name search (namesake possibly non resolved) leading to a need for navigation means; - phonetic search (homonyms with additional distortion), requiring a sophisticated resolution tool. However, users want not only to get information on somebody where they know approximately the name but they want also to identify someone with specific skills, activity or responsibility and whom they probably do not know. Therefore the directory application should enable searches using a selection of criteria taken from the list of preferred items for geographical localization or organizational localization: postal address site building room number company organizational unit division function speciality, activity hierarchical position direct senior officer To be more effective such search tools should include navigation means. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.2.2 Editing facilities | Since paper directories remain very popular, the directory system should allow the printing of a selection of the information sorted according to the user's requirements. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.2.3 Downloading and updating facilities | To fulfil the need for managing their personal customized electronic directory, users need not only to get information from the system in the right shape but they require also that this information be updated from the original database when there is a change, without losing the pieces of information they have added in their own database. If end-users are expected to update some parts of the company directory, the facilities available for that should be user friendly enough to encourage the user to perform this task. TR 101 153-2 V1.1.1 (1998-01) 24 |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.2.4 Interfaces | The interface between the directory system and the end-user terminal should be compatible with the most popular terminals and software. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 8.3 Solutions | Most current directory systems provide advanced searching tools enabling the different kinds of searches described in subclause 8.2.1. Technical solutions for advanced updating as described in subclause 8.2.3 are available in most directory systems. Taking into account the large flexibility needed for searches, downloading and editing facilities, the directory system has, in addition, to provide the same sorting and editing tools as those supplied with most current database systems. These tools could therefore be used by the end-user and by the people in charge of preparing the corporate directory on paper. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9 Management, updating | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9.1 Introduction | The following aspects of management have to be considered: − data management and update; − management of the directory system; − management of the directory service. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9.2 Objectives | Data management has to deal with the directory content for the lifetime of the directory: − schema administration; − who is responsible of which data; − updating organization: regular synchronization as well as real time updating; − access control: who can read, create, modify what? − authentication needs; − etc. Management of the directory system is more or less complex depending on the chosen architecture (centralized, distributed). It has to deal with the current operation of the components of the directory system: − directory domains; − DSAs and DUAs; − replication strategy... TR 101 153-2 V1.1.1 (1998-01) 25 Management of the directory service has to deal with: − quality of service monitoring and reporting: logs, statistics, optimization...; − accounting aspects. The directory designer should have all these issues in mind but the remainder of this clause deals with the management and update of data. Since it would be very difficult to provide a solution for every situation, a list of issues to consider is given hereafter. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9.3 Open issues | A corporate directory is a living thing - it is perpetually changing - as companies change and the people within a company change. People (or objects) whose names and addresses are contained within a directory change their names, change their jobs, change the location they work at. Companies expand or contract the number of locations they operate from, they expand or contract the number of employees at those locations, they take over new companies or divest companies: therefore the directory or directories change accordingly. All these directory changes have to be managed, if not the directory rapidly becomes out of date and because people cannot rely upon it the directory falls into disrepute. An inaccurate directory can often be worse than no directory at all. Therefore if a company is prepared to set up a corporate directory it needs also to be prepared to administer and manage that directory to ensure that it is as accurate as humanly possible. A directory can be managed dictatorially (centralized and strongly controlled) or democratically (decentralized and lightly controlled). The management of a corporate directory system depends upon a number of different factors. 1. Company culture: 1a. Whether or not the company has a centralized or decentralized policy. 1b. The number of changes made by the company (is it a stable company or always changing?). 1c. Relationship of the company locations with each other. 2. The size of the company: 2a. Number of different sites (i.e. factories, offices, depots etc.) which have directory systems. 2b. The number of directory domains and the number of people within each directory domain. 3. The types of systems utilized by a company which require a directory: 3a. Are all the systems requiring directories of the same type? 3b. Does the company have separate directories for telephone, data and e-mail? |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9.3.1 Managing the input | The input to the directory will depend upon whether it is centralized or decentralized. In cases where the directory is decentralized the local system handles the connection between the directory and the end users. In a centralized system the directory is usually maintained in one large database. The input can be downloaded to the central database location from each local site. The personnel function should contribute with a large input into a directory. It is the only function within a company that knows the changes of personnel and when they occur. Far too often a directory becomes the responsibility of an Information Technology support centre and they only receive second hand information and very often late. TR 101 153-2 V1.1.1 (1998-01) 26 Another possibility is to rely on the accounting department for taking care of the directory database management since people in this department have a good view on the staff (wages) and financial flows with partners, customers and suppliers (invoices and bills). |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9.3.2 Managing the output | The output from the directory will depend upon whether it is centralized or decentralized. In cases where the directory is decentralized, the local system handles the connection between the directory and the end users. In a centralized system the directory is usually maintained in one large database. The output for each location can be downloaded to each local site and distributed from there. For a centralized system the input/output function can be automated allowing end-users to access the central database to update or output the data they require. These functions can be carried out by using the electronic mail system. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 9.3.3 Directory Management Standards | The standards requirements and development for directory management represent a considerable problem. The major difficulties are the great diversity of management techniques which can be used for a given number of directory functions. The most appropriate method would be to provide a series of guidelines and recommendations which cover a set of different scenarios. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10 Security - privacy - misuse prevention | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10.1 Introduction | This chapter deals with procedures intended to ensure that data cannot be altered by mistake or malevolence and that any unwanted use of the information be avoided. More precisely: - security is related to how to avoid any unwanted change; - privacy - how to restrict access to the authorized people only; and - misuse prevention - to how to prevent too easy production of lists of people fitting sophisticated combinations of several criteria. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10.2 Objectives | |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10.2.1 Security | Regarding the database, security procedures should ensure that data remain in conformity with the data dictionary and that any piece of information is not entered twice. Regarding the system, security procedures should ensure that people accessing the system can only have access to the information to which they have been given authorization and can change only the information they are allowed to change. This procedure should be further reinforced by the management of information and controls. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10.2.2 Privacy | This issue is related to information with confidential aspects. In general this information is contained in the restricted use directory. In SME or in large companies, this is often a part of the private directory that may only be accessed by authorized people. In any case, this part is restricted to the company's employees but each employee should have access only to his allowed part. TR 101 153-2 V1.1.1 (1998-01) 27 No one other than the authorized persons should have access to any part of the database. This means that strong authentication means are needed to prevent unwanted intrusion in this part. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10.2.3 Misuse prevention | Assuming that, in the near future, information is available on almost everybody in directory systems scattered all over the world, it could be possible, via sophisticated requests, to get a list of all people meeting specific criteria. Many misuses of such lists are easily conceivable and should be avoided. It seems clear that the more meaningful the result of a search, the more confidentiality should be applied. |
ff9f3f41733e8c81bad8a25e26abfb33 | 101 153-2 | 10.3 Open issues | Whatever the solution adopted, misuse of information should not be possible. In particular, obtaining lists of people meeting specific criteria should at least be very slow and/or difficult. TR 101 153-2 V1.1.1 (1998-01) 28 Annex A (informative): X.500 directory technology A.1 What is a directory? A directory is a repository of information about a number of types of objects organized in a particular way. A directory is typically established for some special purposes. There are many examples of directories for different purposes. The most obvious examples are the white pages and the yellow pages of paper telephone directories. A white page directory is used for finding information about a particular person or organization using naming information as the search criterion, while yellow page directories are mostly used for searching for organizations that have some particular characteristics. A price list is an example of directory in which the price can be found for a particular type of item. A department store catalogue is another example, where there can be several pieces of information about a particular type of item. Electronic directories come in many different forms and for different purposes. All e-mail systems have some type of directory for proper handling of mail, e.g. routeing information. Some electronic directories are just configuration tables generated in computer memory during system initialization. A particular interesting directory is the Domain Name Server (DNS) used in the Internet environment to map names to addresses. All types of directories have a common characteristic: they hold information about objects. Objects can be almost anything one would want to store and retrieve information about, such as persons, organizations, computer applications (on-line services), network components, etc.. A.2 The X.500 Directory In 1984 ITU-T (then called CCITT) decided to develop a general purpose directory. The immediate requirement was to provide a directory for Message Handling (X.400). ISO/IEC JTC1 started a similar activity. It was decided quite early to merge the two activities into a single collaborative activity, so as not to produce two different standards for the same purpose. This collaboration on what is called the OSI Directory has worked very well and is still working. The OSI Directory is an OSI application layer standard developed as part of the OSI standardization process. However, the OSI Directory standard has gained wide acceptance also outside the strict area of OSI. The term X.500 or the X.500 Directory is mostly used in preference to the more official title OSI Directory. Here we will often just refer to the Directory. The Directory is specified in the ISO/IEC 9594 multi-part standard and in the ITU-T X.500 Series of Recommendations. The texts in the two sets of documentation specifying the Directory are (with very few and insignificant exceptions) identical. However, ITU-T calls its documents Recommendations, while ISO/IEC calls the same documents International Standards. The term "Specification" has been accepted as a common term. This term is used here. The Directory Specifications are available in three editions: 1988 edition: This is the first edition and is issued as the multi-part standard ISO/IEC 9594: 1990 and as the CCITT X.500 (1988) Series of Recommendations. This edition specifies services, protocols and procedures necessary for basic directory operations. It specifies information models for how information is structured and some commonly usable information objects. In addition, it provides a common framework for general authentication techniques. 1993 edition: This second edition was issued as ISO/IEC9594: and as ITU-T X.500. This edition added some very useful functions, like shadowing of directory information, access control and significantly expanded the information model and administrative capabilities. TR 101 153-2 V1.1.1 (1998-01) 29 1997 edition: This is the third and so far the latest edition. It provides several minor and some extensive extensions. It adds a feature called contexts, which allow information to be distinguished according to the context in which it is being accessed. Another important addition is the provision of OSI Management of the Directory. It has also added and extended important security features. ISO/IEC and ITU-T indicate different years for the same edition, due to different rules. The ITU-T indicates the year in which the work has been approved, and ISO/IEC indicates the year of official publication. The Directory is not intended to be a general purpose database, but has mainly been developed for storing information about objects relevant to telecommunications, such as organizations, persons, distribution lists, OSI application-entities, etc. The information stored about an object is typically information relevant to communication with or about that object, e.g. its communication addresses. The Directory specifications provide an information structure model, protocols for communicating directory information between open systems, and procedures that allow the directory information to be distributed among several independent systems, including procedures for navigation to the open system containing the information to be accessed. An open system can locally maintain its part of the directory information using any suitable database technique. A.3 Directory document structure ISO/IEC 9594-1 | X.500: Overview of Concepts, Models, and Services. ISO/IEC 9594-2 | X.501: Models. ISO/IEC 9594-3 | X.511: Abstract Service Definition. ISO/IEC 9594-4 | X.518: Procedures for Distributed Operation. ISO/IEC 9594-5 | X.519: Protocol Specifications. ISO/IEC 9594-6 | X.520: Selected Attribute Types. ISO/IEC 9594-7 | X.521: Selected Object Classes. ISO/IEC 9594-8 | X.509: Authentication Framework. ISO/IEC 9594-9 | X.525: Replication (not the 1988 edition). ISO/IEC 9594-10 | X.530: Use of Systems Management for Administration of the Directory (only the 1997 edition). The 1988 edition of the Directory Specifications consists of 8 documents, which are the ISO/IEC 9594-1 to ISO/IEC 9594-8 or the corresponding CCITT documents. The 1993 edition includes substantial extension to those parts, although the extensions to Part 8 are minor. Part 9 on Replication is new for the 1993 edition. The 1997 edition adds extensions to most parts. Part 10 on the Use of System Management is new for the 1993 edition. TR 101 153-2 V1.1.1 (1998-01) 30 A.4 Directory Information Tree (DIT) Figure A.1: Directory Information Tree An object for which information is to be stored is represented by an entry in the directory. To store and retrieve information about objects, those objects have to be named. Each object and its corresponding entry have one or more names. A name has to be unambiguous - referring to just one object. However, an object may have more than one name. Directory names are hierarchical in nature and form a naming tree, i.e. in the general case, a name consists of several components reflecting this hierarchy. This naming tree is called the Directory Information Tree (DIT), as a directory entry is associated with each vertex of this tree holding information about the object having the corresponding name. The first level of names below the root is assumed to be names of countries and international organizations. (A country's name is its code taken from ISO 3166 - "Codes for the representation of names of countries"). In the example shown in figure A.1, the next level is the organization, like a company or governmental institution. The full name of an organization is then the country name concatenated with the organization name component, e.g. {C=DK, O=Fallit A/S}. The next two levels in the example are the organizational unit and person. The corresponding names could be {C=DK, O=Fallit A/S, OU=Sales} and {C=DK, O=Fallit A/S, OU=Sales, CN=Jensen}, respectively. The name component added as we move one step down the naming tree is called the Relative Distinguished Name (RDN) for the corresponding entry (and object). The name of an entry is therefore the concatenation of the RDNs from the root down to and including the entry in question. The root does not add any name component. For names to be unambiguous the RDNs for entries just below a particular entry all have to be different. This requires some naming authority or possibly a hierarchy of naming authorities to be in place. An object represented by the Directory always has a so-called distinguished name structured as described above, which is the principal name for the object. An object may also have one or more alias names, which are structured in a similar way. The DIT concept is the very basic directory concept on which most other concepts are built. Several independent directories, i.e. several independent DITs, may be created. However, if the names of the objects represented by these directories are all drawn from the same name space, such directories can be merged into a single directory (provided that they have compatible implementations, information structures, etc.). It is a generally held vision that eventually, with a very few exceptions, all directory information will be part of one "global directory", global in the sense that it is world wide, and global in the sense that it will be common for all directory uses, such as for Message Handling (X.400), EDI, general Internet, etc. The Directory Specifications have been developed with that view in mind and talk in general about the Directory. TR 101 153-2 V1.1.1 (1998-01) 31 A.5 The distributed DIT Figure A.2: The distributed DIT A system that maintains and communicates directory information is called a Directory System Agent (DSA). A directory can be composed of any number of DSAs. Figure A.2 shows a rather simple DIT distributed among four DSAs. The figure also illustrates that the way a DIT can be distributed is very flexible. The entries can be distributed in any way among the DSAs and a DSA does not need to hold a contiguous set of entries. Note, that the root is not an actual entry, it contains no information, and it is not held by any DSA. A.6 The distributed directory Figure A.3: The distributed directory Figure A.3 illustrates the distribution of directory information among DSAs in another way. A user can access directory information by connecting to one of the DSAs. The function supporting the user in this access is called a Directory User Agent (DUA). The DSAs interact in such a way that the user can access information in the directory without needing to know the exact whereabouts of the particular piece of information accessed. The DSAs co-operate by use of distributed TR 101 153-2 V1.1.1 (1998-01) 32 operations to provide this service to the users. The protocol used between two DSAs is called the Directory System Protocol (DSP). The protocol used between a DUA and a DSA is called Directory Access Protocol (DAP). There is an alternative access protocol called Lightweight Directory Access Protocol (LDAP), developed within the Internet Society. LDAP is supported by several Web browsers. In addition, there are also several implementations of Web server/DUA gateways. A.7 Directory Management Domains Figure A.4: Directory Management Domains One or more DSAs and possibly some DUAs may be managed by a single organization. Such a set of systems is called a Directory Management Domain (DMD). A directory is therefore composed of one or more DMDs. Eventually, in a large directory infrastructure there may be thousands of DMDs. The concept of DMDs is only to a limited degree reflected in the X.500 Directory standard. It is more related to how a directory is established with respect to interconnection and with respect to the scope of operation and management. The concept of DMD does not in itself impose restriction on how DSAs are interconnected, but a DMD may for security and management reasons be restricted to only have external communication with other DMDs through a dedicated DSA. For mainly historical reasons, two different types of DMDs have been identified. A Private Directory Management Domain (PRDMD) is a DMD that serves the internal needs of a corporation, organization, or an institution. An Administrative Directory Management Domain (ADDMD) is a DMD run by a public service provider to serve the needs of a public service, like telephony, e-mail, etc. In addition, ADDMDs provide services to PRDMDs by providing the backbone of a directory infrastructure. TR 101 153-2 V1.1.1 (1998-01) 33 Figure A.5: ADDMDs and PRDMDs It should be understood that the distinction between an ADDMD and a PRDMD is not always clear. However, it is useful first to consider the "pure" cases of ADDMDs and PRDMDs. Such a simple view is illustrated in figure A.5. In the simple case there is exactly one ADDMD in a country co-operating with ADDMDs in other countries to provide a directory backbone infrastructure. This ADDMD holds the country entry, and if the country is subdivided, it also holds entries representing smaller locations, like counties. It may hold entries to support particular services, such as an e-mail service. In addition, it may provide a regular service for organizations not wanting to establish their own directory services. A PRDMD has typically an organization entry as its top entry, and its entries form a subtree that is subordinate to the part of the DIT held by the ADDMD. An organization entry can either be subordinate to the country entry, if it is a large national organization, or it can be subordinate to an entry representing a smaller area. It should be noted that even within this somewhat simplified view of a PRDMD, users served by a PRDMD can access information in other PRDMDs without necessarily going through any ADDMD. A PRDMD can hold more than one subtree if it is shared among several organizations. This view of DMDs can be extended to cover the case where there are several ADDMDs in a country, where an ADDMD serves more than one country, where a PRDMD serves an international organization, where a PRDMD also performs some public services, and so on. TR 101 153-2 V1.1.1 (1998-01) 34 History Document history V1.1.1 January 1998 Publication ISBN 2-7437-1920-6 Dépôt légal : Janvier 1998 |
2fc3ee24800832607a894caec2566ade | 101 114 | 1 Scope | The present document identifies the key technical issues and problems of completing the integration of ASN.1 (as defined in the ITU-T Recommendations X.680 [1], X.680 Amendment 1 [2], X.681 [3], X.681 Amendment 1 [4], X.682 [5] and X.683 [6]) and SDL (as defined in ITU-T Recommendations Z.100 [7] and Z.100 Addendum 1 [8]). The present document also identifies the key technical issues and problems of integrating ASN.1 (as defined in the ITU- T Recommendations X.680 [1], X.680 Amendment 1 [2], X.681 [3], X.681 Amendment 1 [4], X.682 [5]) and X.683 [6] and the second version of TTCN (as defined in ISO/IEC 9646-3 [11]). The present document focuses on types and does not investigate representation of values. It is intended that the proposed solutions stated in the present document be used as a basis for further work by ETSI (or others). The present document complements rather than supplants ETR 60 [12] and ITU-T Recommendation Z.105 [9]. |
2fc3ee24800832607a894caec2566ade | 101 114 | 2 References | References may be made to: a) specific versions of publications (identified by date of publication, edition number, version number, etc.), in which case, subsequent revisions to the referenced document do not apply; or b) all versions up to and including the identified version (identified by "up to and including" before the version identity); or c) all versions subsequent to and including the identified version (identified by "onwards" following the version identity); or d) publications without mention of a specific version, in which case the latest version applies. A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same number. [1] ITU-T Recommendation X.680 (1994): "Abstract Syntax Notation One (ASN.1): Specification of basic notation". [2] ITU-T Recommendation X.680 Amendment 1 (1994): "Abstract Syntax Notation One (ASN.1): Specification of basic notation: Rules of extensibility". [3] ITU-T Recommendation X.681 (1994): "Abstract Syntax Notation One (ASN.1): Information object specification". [4] ITU-T Recommendation X.681 Amendment 1 (1994): "Abstract Syntax Notation One (ASN.1): Rules of extensibility". [5] ITU-T Recommendation X.682 (1994): "Abstract Syntax Notation One (ASN.1): constraint specification". [6] ITU-T Recommendation X.683 (1994): "Abstract Syntax Notation One (ASN.1): parametrization of ASN.1 specifications". [7] ITU-T Recommendation Z.100 (1993): "Specification and Description Language (SDL)". [8] ITU-T Recommendation Z.100 Addendum 1 (1996): "Corrections to Recommendation Z.100, CCITT Specification and Description Language (SDL)". [9] ITU-T Recommendation Z.105 (1994): "SDL combined with ASN.1". [10] CCITT Recommendation X.208 (1990) : "Specification of the Abstract Syntax Notation One (ASN.1)". TR 101 114 V1.1.1 (1997-11) 8 [11] TR 101 101 (1997) "Methods for Testing and Specification (MTS); TTCN interim version including ASN.1 1994 support [ISO/IEC 9646-3] (Second Edition Mock-up for JTC1/SC21 Review)". [12] ETR 60 (1995) "Guidelines for using Abstract Syntax Notation one (ASN.1) in telecommunication application protocols". [13] ETS 300 771-1 (1997):"Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; B-ISDN user-network interface layer 3 specification for point-to-multipoint call/connection control; Part 1: Protocol specification; [ITU-T Recommendation Q.2971 (1995), modified]". [14] ITU-T Recommendation X.691 (1995): "ASN.1Encoding Rules: specification of Packed Encoding Rules (PER)". [15] ITU-T COM-10-1-E, Questions allocated to ITU-T study group 10 (Language for telecommunication application) for the study period 1997-2000. |
2fc3ee24800832607a894caec2566ade | 101 114 | 3 Definitions and abbreviations | |
2fc3ee24800832607a894caec2566ade | 101 114 | 3.1 Definitions | For the purposes of the present document, the following definitions apply: ASN.1 94: ASN.1 as defined in the 1994 ITU-T Recommendations X.680 [1], X.680 Amendment 1 [2], X.681 [3], X.681 Amendment 1 [4], X.682 [5] and X.683 [6]. ASN.1 90: ASN.1 as defined in the 1990 ITU-T Recommendation X.208 [10]. |
2fc3ee24800832607a894caec2566ade | 101 114 | 3.2 Abbreviations | For the purposes of the present document, the following abbreviations apply: ASN.1 Abstract Syntax Notation One ASP Abstract Service Primitive ATS Abstract Test Suite BER Basic Encoding Rules BNF Backus-Nauer Form IN Intelligent Network INAP Intelligent Networks Application Protocol IUT Implementation Under Test PER Packed Encoding Rules PDU Protocol Data Units PIXIT Protocol Implementation eXtra Information for Testing SDL Specification and Description Language SUT System Under Test TTCN Tree and Tabular Combined Notation |
2fc3ee24800832607a894caec2566ade | 101 114 | 4 Use of ASN.1 94 in ETSI deliverables | An examination of approximately 1000 ETSI standards produced over the last five years shows that there is a small, but significant, use of ASN.1 (roughly 10%) to describe such things as Protocol Data Units, Remote Operations, Object Identifiers, data for test suites etc. When one considers just higher-layer, management and application protocols the proportionate use of ASN.1 is significantly higher. When ASN.1 is used it is used extensively, for example, in the specification of ISDN supplementary services and of IN protocols, and could not easily be replaced by other techniques. In that sense, ASN.1 is a vital aspect in the specification of ETSI standards. TR 101 114 V1.1.1 (1997-11) 9 There is also a tendency to use ASN.1 in the specification of test suites, even though the base specifications may not use ASN.1. An example of this is the test suites for B-ISDN DSS2 UNI [13] where ASN.1 is used to specify explicitly that Information Elements may appear in any order in a message. This is difficult to express when ASN.1 is not used. ETR 60 [12] recommends the use of ASN.1 94 in preference to older versions of the language. This recommendation is strongly supported by ETSI TC MTS. While many standards still use older versions of ASN.1 there is a growing trend towards the use of ASN.1 94 not only in ETSI standards but also in ITU-T recommendations. For example, • Information Object Classes instead of macros in the definition of Remote Operations; • use of extensibility to leave standards open to future development; • parametrization of ASN.1 specifications for compactness and flexibility; • specification of constraints. One factor that will be significant to the use and acceptance of ASN.1 94 will be the availability of tool support for the new features. The present document identifies the key technical issues and problems of integrating ASN.1 94 and SDL and of integrating ASN.1 94 and TTCN. Clause 5 discusses the issues of integrating ASN.1 94 with SDL. Clause 6 discusses the issues of integrating ASN.1 with TTCN. 5 Problems and issues associated with the use of ASN.1 94 and SDL This clause considers the problems associated with the integration of ASN.1 94 with SDL. The ITU-T Recommendation Z.105 [9] defines how ASN.1 can be used in combination with SDL. However this recommendation only supports partial use of the ASN.1 94, i.e., ITU-T Recommendation X.680 [1] with some restrictions but not the extensions defined in the ITU-T Recommendations X681 [3], X.682 [5] and X.683 [6]. This clause is divided into two parts: the first part considers problems associated with the current ITU-T Recommendation Z.105 [9] definition and the limited ASN.1 94 it is designed to support. The second part considers extensions to the ITU-T Recommendation Z.105 [9] specification necessary to encompass the ASN.1 94 functionality at present not supported. For each problem or feature there is a section containing a description together with some possible solutions and consequences of these solutions. The end of this clause includes a tabular summary of the problems and extensions described. 5.1 Current ITU-T Recommendation Z.105 Issues The intention of ITU-T Recommendation Z.105 [9] is that the structure and the behaviour of systems are described with SDL, while parameters of exchanged messages and internally used data are described with ASN.1. Basically, ITU-T Recommendation Z.105 [9], which is an extension to Z.100 [7], defines: • a new syntax merging the ITU-T Recommendations Z.100 [7] and X.680 [1] syntaxes; • an equivalence between ASN.1 constructs and SDL constructs. ITU-T Recommendation Z.105 [9] allows: • the import of ASN.1 types and values from ASN.1 modules to SDL packages; • the expression of types and values using the ASN.1 syntax embedded in SDL specifications. To a large degree, the version of ASN.1 as defined in ITU-T Recommendation X.680 [1] is supported. The features of ITU-T Recommendations X.681 [3], X.682 [5], and X.683 [6] are not supported. TR 101 114 V1.1.1 (1997-11) 10 5.1.1 Restrictions on ITU-T Recommendation X.680 imposed by Z.105 Because of the integration of the concepts and of the syntaxes of ASN.1 and SDL, ITU-T Recommendation Z.105 [9] defines a set of restrictions on ITU-T Recommendation X.680 [1]. These restrictions limit the possibility to use existing ASN.1 material with SDL. 5.1.1.1 Description 5.1.1.1.1 Mapping restrictions These restrictions apply both when ASN.1 definitions are imported into SDL from an external module or when the ASN.1 syntax inside SDL is used. This could be a potential problem when there is a need to import existing ASN.1 material into SDL packages, because there is a likelihood that these ASN.1 modules are not compliant with these restrictions. The mapping restrictions are: • case sensitivity is not supported. The motivation for this restriction is that SDL is case insensitive. This restriction implies that introducing two types with the same name (apart from case sensitivity) is an error. However, it is allowed to have the same name if they are of different entity classes. Entity classes are for example, type names, value names and identifiers; • the use of the same identifier for named numbers or named bits of different types in the same scope shall be avoided. The motivation is that named numbers and named bits are mapped on SDL integer synonyms. Using the same identifier twice would result in illegal SDL (redefinition of the same synonym). Double use of the same identifier in different enumerated types, or in an enumerated type and in a named integer or named bit is allowed, because the identifiers in enumerated types are not mapped on integer synonyms; • the OBJECT IDENTIFIER component values that are assigned by ITU-T, ISO, or both, are not defined in the package called Predefined. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.1.1.2 Syntax differences when using ASN.1 syntax inside SDL | The syntax differences when using ASN.1 syntax embedded in SDL are: • the dash in ASN.1 names is not supported inside SDL descriptions. Dashes are allowed in names within ASN.1 modules that are imported in SDL, but when they are imported in SDL, the dashes should be transformed to underscores. The motivation for this restriction is that the dash is considered as the minus operator in SDL; • definitions must be ended with a semi-colon; • ASN.1 type REAL is not represented as a sequence of integers, as is the case in ITU-T Recommendation X.680 [1]. The value notation of ITU-T Recommendation X.208 [10] shall be used instead, i.e., { 314, 10, -2 } should be used instead of { mantissa 314, base 10, exponent -2 }. Alternatively, the SDL syntax for denoting REAL values can be used, i.e., 3.14 is also allowed. As a consequence, no subtyping of mantissa, base, or exponent is allowed, and no operators for accessing or changing the mantissa, base, or exponent of a REAL value are supported; • in external type and value references, spaces shall be put around the period (.). 5.1.1.2 Solution A: Make recommendations on the use of ITU-T Recommendation X.680 |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.1.2.1 Solution description | Make recommendations on the use of ASN.1, so as to facilitate the reuse of ASN.1 modules in the scope of SDL specifications. They should apply both to the ASN.1 modules developed on their own and to the ASN.1 embedded in SDL. TR 101 114 V1.1.1 (1997-11) 11 Some examples of guidelines are: • two entities of the same class shall not be identical once put in lower case; • the use of the same identifier for named numbers or named bits of different types in the same scope should be avoided. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.1.2.2 Solution consequences | Conformance to these rules ensures the possibility to import ASN.1 entities from ASN.1 modules to SDL specifications provided only ITU-T Recommendation X.680 [1] is used. Whereas, SDL specifications importing ASN.1 modules not conforming to the mapping restriction could be semantically incorrect from the ITU-T Recommendation Z.105 [9] point of view. For example, consider two types defined in an ASN.1 module with names identical apart from the cases. Import of these two types into SDL will have the effect to define the same type twice. NOTE: The rules defined above do not prevent name clashes when importing two ASN.1 modules into the same SDL specification. This is a general problem which could be solved by prefixing entity names with module reference. 5.1.2 Non-support of ITU-T Recommendation X.680 Amendment 1, ITU-T Recommendations X.681, X.682 and X.683 |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.2.1 Description | Consider the case where ASN.1 94 is already used in some ETSI standards and there is a need to import these ASN.1 definitions into SDL specifications. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.2.1.1 Solution A: Limit the use of ASN.1 to ITU-T Recommend | ation X.680 |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.2.1.1.1 Solution description | Restrict the use of ASN.194 to ITU-T Recommendation X.680 [1] only. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.2.1.1.2 Solution consequences | This solution will guarantee that the ASN.1 modules can be imported into SDL. But this will limit strongly the use of ASN.1 94 and will be in contradiction with ETR 060 [12]. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.2.1.2 Solution B: Make recommendation to ease the reuse of | ASN.1 94 |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.2.1.2.1 Solution description | Transform the ITU-T Recommendation X.680-series features to equivalent constructs in ITU-T Recommendation X.680 [1]. NOTE: This transformation would have to be done manually. Of course, the support of these transformations by a tool would be of interest. TR 101 114 V1.1.1 (1997-11) 12 definitions in ASN.1 94 transformation according to rules taking into account ITU-T Recommendation Z.105 [9] limitations equivalent definitions in ITU-T Recommendation X.680[1] SDL Import written according to guide lines Figure 1: Transformation to ITU-T Recommendation X.680 [1] The transformations would consist mainly of: • removing the extension marker (=> no extensibility in the SDL model); • resolve parametrization (arduous but not difficult); • resolve constraints. This is probably the most difficult point. Ways to imitate the table constraint mechanism would have to be defined. (probably with CHOICEs) (=> instanciations of information objects); • replace remaining uses of information objects, object classes and object sets, by appropriate types and values, then remove the declarations of these objects, classes and sets; • redefine the appropriate types for entities which have not been mapped in ITU-T Recommendation Z.105 [9]. 5.1.2.1.2.2 Solution consequences The use of ASN.1 94 specifications in SDL as defined in ITU-T Recommendation Z.105 [9] will be facilitated (to a degree). Nevertheless manual transformation of ASN.1 definitions will remain a tedious work. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.1.3 Defects in ITU-T Recommendation Z105 | Defects in ITU-T Recommendation Z.105 [9] could constitute a limitation to the use of the present document. A significant number of defects, most of them are editorial, have been identified and are described in the ITU-T document COM-10-1 [15]. ITU-T will maintain a Master list of changes containing corrections or clarification corresponding to these defects. These changes will be incorporated in the next version of ITU-T Recommendation Z.105 [9]. In addition the following problems have been identified: • Type constraints are supported in a limited way: • exceptions are not supported (ITU-T Recommendation X. 680 [1] BNF productions Constraint ::= "(" ConstraintSpec ExceptionSpec")" and ExceptionSpec ::= "!" ExceptionIdentification | empty); • intersections in subtype constraints are not supported (but unions are). (ITU-T Recommendation X. 680 BNF productions SubtypeConstraint ::= ElementSetSpec and the following); • exclusions in subtype constraints are not supported; • some predefined types are not supported, e.g., TeletexString. TR 101 114 V1.1.1 (1997-11) 13 5.2 Extensions to ITU-T Recommendation Z.105 to support ASN.1 94 more completely ITU-T Recommendations X.680 Amendment 1 [2], X.681 [3], X.681 Amendment 1 [4], X.682 [5] and X.683 [6] are not addressed by ITU-T Recommendation Z.105 [9]. The support of these extensions is desirable. Moreover, the use of these features is encouraged by ETR 60 [12]. ASN.1 modules using these concepts, especially information objects and parametrization, will be of particular interest. The table 1 of ITU-T Recommendation Z.105 [9] summarizing the data characteristics of SDL, ASN.1 and their combination could be complemented as follows (the first line has been added): Table 1: Characteristics of SDL and ASN.1 SDL ASN.1 SDL/ASN.1 Definition of object classes, information objects and object sets X X Definition of types X X X Notation for values X X X Definition of operators X X Expressions X X Encoding of values X X NOTE: The last line of the table is not strictly correct as ASN.1 94 (i.e., the ITU-T Recommendation X.680- series) does not allow the definition of encoding. However, the ITU-T Recommendation X.690-series does define encoding rules (e.g., ITU-T Recommendation X.691 [14] that can be applied on ASN.1 types and values. ITU-T Recommendation Z.105 [9] models cannot contain specification of encoding, except as informal text. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.1 ITU-T plans for the evolution of ITU-T Recommendation Z.1 | 05 At the time of writing, ITU-T plans to issue new versions of ITU-T Recommendations Z.100 [7] and Z.105 [9] by the year 2000 to keep SDL in line with developing technologies. ITU-T Recommendation Z.105 [9] is concerned by the following ITU-T decisions: • The underlying data model of this so-called SDL-2000 language will no longer be ACT ONE but a more powerful and more implementable data model, still to be defined. Consequently the mapping rules of ASN.1 definitions to SDL data concepts will have to be changed to reflect the new data model. • ITU-T Recommendation Z.105 [9] will continue to be a document separate from Z.100 [7]. • ITU-T Recommendation Z.100 [7] will be updated so that Z.105 [9] does not need to redefine ITU-T Recommendation Z.100 [7]. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2 Syntax considerations | ITU-T Recommendation Z.105 [9] has the philosophy to merge completely the ASN.1 and SDL syntaxes, though the complete mixing of the notations is discouraged to the user. Keeping this philosophy to incorporate the ASN.1 94 extensions will result in a complex grammar. Therefore alternatives solutions allowing the import of ASN.1 material from ASN.1 modules but not their definition inside SDL specifications have been investigated. Concerning the syntax, three levels of integration to allow the use of ASN.1 94 with SDL can be envisaged. Each level defines a way to complement the ITU-T Recommendation Z.105 [9] grammar. The following example illustrates these three possible solutions: ModuleA DEFINITIONS ::= BEGIN TR 101 114 V1.1.1 (1997-11) 14 -- definition of an object class PARAMETERS-BOUND ::= CLASS { &minLength INTEGER, &maxLength INTEGER } WITH SYNTAX { MINIMUM-FOR-LENGTH &minLength MAXIMUM-FOR-LENGTH &maxLength } -- definition of a type parameterized by an object class ParamType {PARAMETERS-BOUND : bound} ::= OCTET STRING (SIZE(bound.&minLength..bound.&maxLength)) -- information object, instance of the class PARAMETERS-BOUND networkSpecificBoundSet PARAMETERS-BOUND ::= { MINIMUM-FOR-LENGTH 3 MAXIMUM-FOR-LENGTH 5 } -- definition of a parameterized type List1 { ElementTypeParam } ::= SEQUENCE { elem ElementTypeParam, next List1 { ElementTypeParam } OPTIONAL } -- definition of a parameterized value genericString { IA5String : name } IA5String ::= { "Name : ", name} END |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.1 Solution A: Full integration of ASN.1 94 and SDL | |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.1.1 Solution description | This solution consists in complementing the ITU-T Recommendation Z.105 [9] grammar so that the ASN.194 and SDL syntaxes are merged. This solution complies with the syntactic approach taken for the current ITU-T Recommendation Z.105 [9]. Both the import of all classes of ASN.1 entities, e.g., information object set, parametrized type, and their definition inside SDL are permitted. NOTE: Though it is permitted, ITU-T Recommendation Z.105 [9] discourages the definition of ASN.1 types inside SDL packages. The ASN.1 module defined above can be imported to SDL as described in solution B, but equivalently the same definitions could be inserted directly in a SDL package as follows: system example ... /* definition of an object class */ PARAMETERS_BOUND ::= CLASS { &minLength INTEGER, &maxLength INTEGER, } WITH SYNTAX { MINIMUM_FOR_LENGTH &maxLength MAXIMUM_FOR_LENGTH &maxLength } ; /* definition of a type parameterized by an object class */ ParamType {PARAMETERS_BOUND : bound} ::= OCTET STRING (SIZE(bound.&minLength..bound.&maxLength)) ; /* information object, instance of PARAMETERS_BOUND */ networkSpecificBoundSet PARAMETERS-BOUND ::= { MINIMUM_FOR_LENGTH 3 MAXIMUM_FOR_LENGTH 5 } ; /* definition of a parameterized type */ TR 101 114 V1.1.1 (1997-11) 15 newtype List1 { ElementTypeParam } SEQUENCE { elem ElementTypeParam, next List1 { ElementTypeParam } OPTIONAL } ; /* definition of a parameterized value */ genericString { IA5String : name } IA5String ::= { "Name : ", name} ; ... endsystem example; |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.1.2 Solution consequences | This solution conforms with the philosophy adopted for the current ITU-T Recommendation Z.105 [9]. This results in a homogeneous definition. On the other hand the ITU-T Recommendation Z.105 [9] grammar must be enriched with numerous Backus-Nauer Form (BNF) productions which would result in a more complicated standard. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.2 Solution B: Allow import of ASN.1 94 module from SDL, a | nd the use of imported entities in SDL |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.2.1 Solution description | This solution allows: • The import of all class of entities (types, values, information objects, object class, object sets) defined in an ASN.1 94 module. • The use of these imported entities in SDL. This solution does not permit the definition of ITU-T Recommendations X.681 [3], X.682 [5] and X.683 [6] entities (information objects, object class, object sets, parametrized types, constraints) inside SDL. The import of all class of ASN.1 entity (types, values, classes, object, object sets) from ASN.1 modules to SDL definitions and the use of this material is authorized. For instance, an SDL model making use of moduleA can be: use moduleA ; ... process myproc; dcl /* use of a type parameterized by an information object */ mygvns ParamType { networkSpecificBoundSet }, /* use of a type parameterized by a type */ myintlist List1 {INTEGER}, mymax integer, mystring IA5String; start; /* use of an information object value */ task mymax := networkSpecificBoundSet.&maxLength; /* use of a parameterized value */ task mystring := genericString { "John" }; endprocess myproc; The affected ITU-T Recommendation Z.105 [9] BNF productions could be: <sort constructor> ::= ...existing Z.105 non-terminals ... <object class field type> <from object> <extended primary> ::= ...existing Z.105 non-terminals ... <object class field value> <from object> <object class field value> ::= [ <sort> : ] <expression> <from object> ::= [ <package name> . ] { <object name> | <object set name> } [ { <actual parameter> { , <actual parameter> } * } ] . <field name> <actual parameter> ::= <sort> | <extended primary> <object class field type> ::= <defined object class> . <field name> <defined object class> ::= {[ <package name> . ] <object class name>} | TYPE-IDENTIFIER | ABSTRACT- SYNTAX TR 101 114 V1.1.1 (1997-11) 16 |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.2.2 Solution consequences | In this solution the ITU-T Recommendation Z.105 [9] grammar is extended in a limited way. All the possibilities of mixing ASN.1 and SDL, e.g., defining information objects in a SDL package, are not possible but this is discouraged by ITU-T Recommendation Z.105 [9] anyway. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.3 Solution C: Allow import of ASN.1 94 module from SDL, k | eep the ITU-T Recommendation Z.105 syntax unchanged. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.3.1 Solution description | This solution consists in only allowing the import of fully defined types and values. To be able to make use of generic types and values defined by ModuleA, an intermediate module must be defined as follows: ModuleB DEFINITIONS ::= BEGIN IMPORTS ParamType, PARAMETERS-BOUND, networkSpecificBoundSet, List1, genericString FROM ModuleA; NetworkSpecificParamType ::= ParamType { networkSpecificBoundSet }, IntegerList1 ::= List1 { INTEGER } networkSpecificMaxLength:= networkSpecificBoundSet.&maxLength; johnBirthdayGreeting := genericString { "John" }; END The SDL specification becomes: use moduleB; ... dcl mygvns NetworkSpecificParamType , myintlist IntegerList1, mymax integer, mystring IA5String; start; task mymax := networkSpecificMaxLength; task mystring := johnBirthdayGreeting; endprocess myproc; |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.2.3.2 Solution consequences | The main advantage of this solution is that few changes to the ITU-T Recommendation Z.105 [9] are required, none at the syntax level. On the other hand the user has to define intermediate ASN.1 modules to be able to make use of parametrized entities. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.3 Information objects | ASN.1 94 allow the definition of ASN.1 modules intended to work with any of a number of instances of some class of information objects. ITU-T Recommendation X.681 [3] specifies a notation for defining information object classes and instanciations of these classes, and a notation for extracting information from objects. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.3.1 Solution description | The proposed solution would complement ITU-T Recommendation Z.105 [9] with the support of information objects. Nevertheless from the semantic point of view, no equivalence would be defined between information objects and existing SDL concepts (the equivalence defined by ITU-T Recommendation Z.105 [9] remains at the level of types and values). An exception for this statement could concern table constraints. This issue is discussed in subclause 5.2.3. TR 101 114 V1.1.1 (1997-11) 17 The following example illustrates the possible use of information objects in SDL: Consider the following information object class and information object: MY-OBJECT-CLASS ::= CLASS { &valueField INTEGER, &TypeField } WITH SYNTAX { VALUE-FIELD &valueField, TYPE-FIELD &typeField } myInfoObject MY-OBJECT-CLASS ::= { VALUE-FIELD 96 TYPE-FIELD REAL } Once imported, the following use of myInfoObject in SDL will be possible: /* use of ASN.1 types and values */ dcl a Integer := myInfoObject.&valueField; dcl b myInfoObject.&typeField; The following use will not be correct because no equivalence between ASN.1 information object classes and SDL sorts is defined: /* Incorrect: declaration of a variable for an object class */ dcl c MY_OBJECT_CLASS := myInfoObject; As generally presented in subclause 5.2.1, three solutions for the support of information objects can be envisaged: • solution A of 5.2.1: inclusion of the notation for defining objects, class and sets, and of the notation for extracting information, into the SDL grammar; • solution B of 5.2.1: inclusion of the notation for extracting information; • solution C of 5.2.1: no notation for information objects included in the SDL grammar. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.3.3 Solution consequences | The solution enables the import of modules using information objects which is a key feature of ASN.1 94. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4 Open types | |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.1 Description | ASN.1 94 define features making types and values generic: parametrization, type openness, specification of constraints. It is essential that the types are fully instanciated when used in SDL. In replacement of the ANY notation, ASN.1 94 allows the definition of open types. The open type notation consists in the ObjectClassFieldType production specified in ITU-T Recommendation X.681 [3], where the FieldName denotes either a type field or a variable-type value field. Consider the following definition of the type ErrorReturn ERROR-CLASS ::= CLASS { &code INTEGER, &Type } ErrorReturn ::= SEQUENCE { errorCode ERROR-CLASS.&code, errorInfo ERROR-CLASS.&Type } TR 101 114 V1.1.1 (1997-11) 18 |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.2 Solution A: No support of open types | |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.2.1 Solution description | As the exact type of errorInfo is not known an equivalent SDL definition cannot be determined. The proposed solution consists in not allowing the use of open types. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.2.2 Solution consequences | This solution could be felt as a strong limitation. In particular, the use of the InstanceOfType notation which is a shorthand notation for defining an open type constrained by an information object set of a class derived from the TYPE- IDENTIFIER predefined class, and is recommended by ETR 60 [12] when there is a need for embedding information from another protocol, will not be possible. |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.3 Solution B: Support of open types constrained with tabl | es (information object sets) |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.3.1 Solution description | ITU-T Recommendation X.682 [5] defines the constraint table notation which enables to specify that the type of an item depends on the value of another item with the help of information object sets. ERROR-CLASS ::= CLASS { &code INTEGER, &Type } WITH SYNTAX {&code &Type} ErrorSet ERROR-CLASS ::= { {1 INTEGER} | {2 REAL} } ErrorReturn ::= SEQUENCE { errorCode ERROR-CLASS.&code ({ErrorSet}), errorInfo ERROR-CLASS.&Type ({ErrorSet}{@errorCode}) } The possible types that errorInfo could take are specified (INTEGER or REAL). Consequently an equivalent SDL construct could be defined. The equivalence could be close to the one defined for the CHOICE construct. The following type definition is not strictly equivalent to the one given above but gives a first idea of the kind of transformation that can be applied on table constraints to implement them in SDL. ErrorReturn ::= SEQUENCE { errorCode INTEGER, errorInfo CHOICE { code1 INTEGER, code2 REAL } } |
2fc3ee24800832607a894caec2566ade | 101 114 | 5.2.4.3.2 Solution consequences | Types constrained by object sets will be allowed, thus extending the coverage of ASN.1 94. The use of the InstanceOfType notation, which is a shorthand notation for defining an open type constrained by an information object set of a class derived from the TYPE-IDENTIFIER predefined class, will be possible as well. A model, which could be complex, for the translation of these ASN.1 constructs to SDL should be determined. |
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