Base_JSON/prefixJ/json/J78/J78-3011.json

{
    "paper_id": "J78-3011",
    "header": {
        "generated_with": "S2ORC 1.0.0",
        "date_generated": "2023-01-19T03:04:28.098786Z"
    },
    "title": "Taxonomic Lattice Structures for Situation Recognitiom",
    "authors": [
        {
            "first": "William",
            "middle": [
                "A"
            ],
            "last": "Woods",
            "suffix": "",
            "affiliation": {},
            "email": ""
        },
        {
            "first": "Bolt",
            "middle": [],
            "last": "Beranek",
            "suffix": "",
            "affiliation": {},
            "email": ""
        },
        {
            "first": "Newman",
            "middle": [],
            "last": "Inc",
            "suffix": "",
            "affiliation": {},
            "email": ""
        },
        {
            "first": "'",
            "middle": [],
            "last": "50 Moulton S T R E E T Cambridge",
            "suffix": "",
            "affiliation": {},
            "email": ""
        }
    ],
    "year": "",
    "venue": null,
    "identifiers": {},
    "abstract": "",
    "pdf_parse": {
        "paper_id": "J78-3011",
        "_pdf_hash": "",
        "abstract": [],
        "body_text": [
            {
                "text": "Intelligent Machine m e k i n d s of i n t e l l i g e n t computer a s s i s t a n t s t h a t we wguld l i k e to be a b l e t o construct a r e very much like i n t e l l i g e n t organisms i n t h e i r own r i q h t .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "The Role of a Knowledge Network for an",
                "sec_num": "1."
            },
            {
                "text": "for a moment an i n t e l l i g e n t organism trying t o g e t along i n t h e world ( f i n d enough food , * s t a y out of trouble, s a t i s f y basic needs, e t c . ) .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "The most valuable service played by an i n t e r n a l knowledge base for s u c h an organism is t o repeatedly answer question6 l i k e \"what's going on out /there?\" , \"can it harm me?\" , \"how can I avoid/placate i t ? \" , \" I s . it 'good t o e a t ? \" , w I s t h e r e any s p e c i a l thing I should do about i t ? \" , e t c .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "To support t h i s k i n d of a c t i v i t y , a s u b s t a n t i a l p a r t of the knowledge base m u s t be organi>ed as a recognition device for c l a s s i f y i n g and i d m t i f y i n g s i t u a t i o n s i n the world. The major purpose of t h i s s i t u a t i o n recognition is t o locate i n t e r n a l procedures which a r e applicable (appropriate, permitted, mandatory, e t c .) t o the current s i t u a t i o n . I n constructing an i n t e l q i g e n t computer a s s i s t a n t , t h e -r o l e s of knowledge a r e very simil'ar.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "The basic goals of food g e t t i n g and danger avoidance a r e replaced by goals of doing .what the user wants and avoiding things that the machine has been instructed t o avoid. However, the fundamental problem of analyz in'g a s i t u a t i o n (one established e i t h e r l i n g u i s t i c a l l y or physically or by some cambination of the two) i n order t o determine whether i t is one for which t h e r e a r e procedures t o Be executed, or one which was to be avoided (or one which might lsad t o one t h a t is t o be avoided) , e t c . i s b a s i c a l l y the same. For example, dne might want t o i n s t r u c t such a system t o remind t h e user i n advance of any upcoming scheduled meetings, t o inform h i m i f h e t r i e s t o assign a resource t h a t has already been committed, t o always p r i n t out meehges i n reverse chronological order (when requested), t o assume that \" t h e f i r s t a r e f e r s t o t h e f i r s t day of the upcoming month i n a f u t u r e s c h e d u l h g context and the f i r s t day of the current mo-nth i n a past context,, e t c .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "I h e principal role of the knowledge network for such a system is e s s e n t i a l l y t o serve as a \"coat rack\" upon which t o hang vat ious pieces of advice for the system t o execute.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "Thus the notion of procedural attachment becomes not just an e f f i c i e n c y technique, b u t the main purpose for the existence of t h e network. This does not necessarily imply, however, t h a t the procedures involved c o n s i s t of low-level machine code. @ey may instead, and probably usually w i l l , be high level s p e c i f i c a t i o n s of things t o be done or goals t o be achieved.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "The p r i n c i p a l s t r u c t u r e t h a t organizes a l l , of these procedures is a conceptual tax~nomy of s i t u a t i o n s about which t h e machine knows something . support the above uses of knowledge, an important character i s t i c required of an e f f icienk knowledge representation seems t o be a mechanism of inheritance t h a t w i l l permit i'nEormation t o be stored i n its most general form and y e t s t i l l be triggered by any more s p e c i f i c situ&Eion or instance t o which i t a p p l i e s .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "Moreover, t h e nodes i n t h e network (or. at l e a s t a major c l a s s of nodes) should be i n t e r p r e t a b l e a s s i t u a t i o n descriptions.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "One of t h e most fundamental kinds of information t o be s t w e d i n the knowledge base w i l l be r u l e s of the form \" i f < s i t u a t i o n description> is s a t i s f i e d then do t a c t i o n description>\", or \"if < s i t u a t i o n description) then expect < s i t u a t i o n description>\". * * S i t u a t i o n descr i p t ions a r e i n general c h a r a c t e r i z a t i o n s of c l a s s e s of s i t u a t i o n s t h a t the machine could he i n .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "They a r e not complete descriptions of world s t a t e s , b u t only p a r t i a l descriptions t h a t apply t o c l a s s e s of worla s t a t e s .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "(The machine should never be assumed or required t o have a complege d e s c r i p t i o n of a world s t a t e if i t is t'd deal w i t h the r e a l world.) A s i t u a t i o n i n t h i s p a r t i a l u n s e is defined by the r e s u l t s of certain measurements, namputations, or recognition procedures applied to the systemg s input. Examples of s*uations might be ' Y o u have a goal to achieve which is an example of s i tua t ion Y\"",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "\"You a r e perceiving an o b j e c t of class Z\", \"'Ihe user has asked you t o perform a task of type W n , etc. ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Imagine",
                "sec_num": null
            },
            {
                "text": "t h e system. However, t h e r e are i n g e n e r a l many t3i f f e r e n t ways i n which t h e c u r r e n t ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "C o n c e p t u a l l y , one m i g h t t h i n k of t h e p r o c e s s o f a c t i v a t i n g a l l of t h e d e s c r i p t i o n s t h a t a r e s a t i s f i e d by t h e c u r r e n t s i t u a t i o n as one of t a k i n g a d e s c r i p t i o n of t h e c u r r e n t s i t u a t i o n and matching it a g a i n s t d e s c r i p t i o n s s t o r e d i n",
                "sec_num": null
            },
            {
                "text": "A s s u g g e s t e d above, t h e p r o c e s s of r e c o g n i z i n g t h a t a c u r r e n t s i t u a t i o n is an i n s t a n c e of a n i n t e r n a l s i t u a t",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "2, Parsing Situations",
                "sec_num": null
            },
            {
                "text": "That is, whereas t h e pt i n c i p a l r e l a t i o n s h i p between c o n s t i t u e n t s i n s e n t e n c e s is m e r e l y a d j a c e n c y i n t h e i n p u t s t r i n g , t h e r e l a t i o n s h i p s among c o n s t i t u e n t s of a A l t e r n a t i v e l y , i f t h e r e is some p a r t i c u l a r p a r t i c i p a n t t h a t by v i r t u e of its type s t r o n g l y s u g g e s t s what s i t u a t i o n d e s c r i p t i o n s it might p a r t i c i p a t e i n , t h e n an index from t h i s p a r t i c i p a n t might select a more manageable set of s i t u a t i o n d e s c r i p t i o n s t o t e s t . Even i n t h i s c a s e , however, t h e number of s i t u a t i o n s i n which t h e c o n s t i t u e n t c o u l d p a r t i c i p a t e may s t i l l be t~o l a r g e t o t e s t e f f i c i e n t l y . I n t h e most d i f f i c u l t s i t u a t i o n , no s i n g l e p a r t i c i p a n t i n t h e i n p u t is s u f f i c i e n t l y s u g g e s t \" n o t t h a t much\"), t h e r e is no s i n g l e word t h a t is s t r o n g l y s u g g e s t i v e of t h e i n t e r p r e t a t i o n of t h e s e n t e n c e .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "i o n d e s c r i p t i o n is s i m i l a r t o t h e p r o c e s s of p a r s i n g a s e n t e n c e ; a l t h o u g h c o n s i d e r a b l y more d i f f i c u l t due t o a more open-ended s e t u o f p o s s i b l e r e l a t i o n s h i p s among t h e n c o n s t i t u e n t s n bg a s i t u a t i o n .",
                "sec_num": null
            },
            {
                "text": "v i o u d d i s p i a y .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "MoreoQer, t h e r e is n o t h i n g e x p l i c i t t o s u g g e s t t h e r e l a t i o n s h i p of t h i s c l a u s e t o t h e one t h a t follows t h e semicolon. !Che l a t t e r , i f i n t e r p r e t e d i n i s o l a t i o n , would m e r e l y be a r e q u e s t f o r a d i s p l a y , perhagbe a s u c c e s s i o n of t w o d i s p l a y s , g h i l e i n t h e c o n t e x t g i v e n , it is a r e q u e s t t o modify a p r e",
                "sec_num": null
            },
            {
                "text": "There a r e . two methods t h a t I b e l i e v e may be s u f f i c i e n t , e i t h e r i n d i I have been i n v e s t i g a t i n g a s t r u c t u r e which I c a l l a \"taxonomic l a t t i c e n , t h a t combines some f e a t u r e s of both methods.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "MoreoQer, t h e r e is n o t h i n g e x p l i c i t t o s u g g e s t t h e r e l a t i o n s h i p of t h i s c l a u s e t o t h e one t h a t follows t h e semicolon. !Che l a t t e r , i f i n t e r p r e t e d i n i s o l a t i o n , would m e r e l y be a r e q u e s t f o r a d i s p l a y , perhagbe a s u c c e s s i o n of t w o d i s p l a y s , g h i l e i n t h e c o n t e x t g i v e n , it is a r e q u e s t t o modify a p r e",
                "sec_num": null
            },
            {
                "text": "v i d u a l l y or i n kombinat i o n ,",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "MoreoQer, t h e r e is n o t h i n g e x p l i c i t t o s u g g e s t t h e r e l a t i o n s h i p of t h i s c l a u s e t o t h e one t h a t follows t h e semicolon. !Che l a t t e r , i f i n t e r p r e t e d i n i s o l a t i o n , would m e r e l y be a r e q u e s t f o r a d i s p l a y , perhagbe a s u c c e s s i o n of t w o d i s p l a y s , g h i l e i n t h e c o n t e x t g i v e n , it is a r e q u e s t t o modify a p r e",
                "sec_num": null
            },
            {
                "text": "Given a knowledge-based system w i t h l a r g e numbers of s i t u a t i o n -a c t i o n rules, where it is i n f e a s i b l e t o f i n d t h e r u l e s t h a t match a g i v e n s i t u a t i o n by s y s t e m a t i c a l l y c~n s i d e r i n g each r u l e , one n e e d s t o have some way of r e d u c i n g t h e c o m p u t a t i o n a l l o a d . A s mentioned b e f o r e , one a p p r o a t h i s t o index t h e r u l e s a c c o r d i n g t o some s a l i e n t f e a t u r e t h a t w i l l be e a s i l y d e t e c t a b l e i n t h e irtjput s i t u a t i o n and can t h e n be used t o f i n d a much more l i m i t e d s e t of r u l e s t o apply. This h a s been done i n many s y s t e m s , i n c l u d i n g t h e LUNAR system f o r n a t u r a l l a n g u a g e q u e s t i o n answering [Woods, 1973, 19771 . Another problem is t h a t a g i v e g s i t u a t i o n may be matched by s e v e r a l r u l e s s i m u l t a n e o u s l y w i t h d i f f e r i n g d e g r e e s of g e n e r a l i t y .",
                "cite_spans": [
                    {
                        "start": 818,
                        "end": 837,
                        "text": "[Woods, 1973, 19771",
                        "ref_id": null
                    }
                ],
                "ref_spans": [],
                "eq_spans": [],
                "section": "37",
                "sec_num": null
            },
            {
                "text": "For example, t h e r e m y be a r u l e t h a t s a y s \"whenever a c c e s s among which t h e a t t r i b u t e \" c l a s s i f ied\" is n o t p a r t i c u l a r l y s a l i e n t -.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "37",
                "sec_num": null
            },
            {
                "text": "Another t e c h n i q u e t h a t h o l d s promise f o r s i t u a t i o n r e c o g n i t i o n is the use of a markable c l a s s i f i c a t i o n s t r u c t u r e i n which c o i n c i d e n c e s of r e l a t i v e l y n o n -s a l i e n t e v e n t s can be d e t e c t e d . The keystone o f t h i s approach is a technique : t h a t Q u i l l i a n proposed f o r modeling c e r t a i n a s p e c t s of human a s s o c i h t i v e memory [QuilT i a n , 1966, 19681 . Q u i l l i a n I s t e c h n i q u e of \"semantic i n t e r s e c t i o n \" c o n s i S t e d of p r o p a g a t i n g t r a c e s of \" a c t i v a t i o n \" through a semantic network s t r u c t u r e so t h a t c o n n e c t i o n p a t h s r e l a t i n g a r b i t r a r y c o n c e p t s could be d e t e c t e d .",
                "cite_spans": [
                    {
                        "start": 464,
                        "end": 469,
                        "text": "1966,",
                        "ref_id": null
                    },
                    {
                        "start": 470,
                        "end": 475,
                        "text": "19681",
                        "ref_id": null
                    }
                ],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Markable Classification Structures 3g",
                "sec_num": "3.2"
            },
            {
                "text": "For example, h i s system was a b l e t o c c n n e c t c o n c e p t s snch a s \" p l a n t n and \"nour ishment\" by d i s c o v e r inq the \" c h a i n w e q u i v a l e n t t o \" p l a n t s draw nourishment fkom t h e s o i l \" . ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Markable Classification Structures 3g",
                "sec_num": "3.2"
            },
            {
                "text": "I f t h i s were necessa-ry, t h e n a l l of t h e advantage of s e a r c h i n g from both e n d s would be lost,",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "t e e f f i c i e n t l y i f t h e a l g o r i t h m is c a p a b l e of p u t t i n g marks i n t h e s t r u c t u r e of t h e maze i t s e l f ( o r some s t r u c t u r e isomorphic t o it), s o t h a t it can t e l l when r e a c h i n g a g i v e n node whether a p a t h from t h e soulrce or t h e g o a l h a s a l r e a d y reached t h a t node. However, w i t h o u t such a b i l i t y t o mark the nodes o f t h e maze>, t h e p r o c e s s of t e s t i n g whether a g i v e n path from t h e s o u r c e c a n hook up w i t h a p a t h from t h e g o a l would i n v o l v e a s e a r c h thrnugh a l l t h e p a t h s from t h e g o a l i n d i v i d u a l l y , and a s e a r c h down each such p a t h t o see i f t h e node a t t h e end of t h e sodrce p a t h o c c u r r e d anywhere on t h a t p a t h ,",
                "sec_num": null
            },
            {
                "text": "Th e c o i n c i d e n c e of a p a t h from t h e s o u r c e m e e t i~g a p a t h from t h e g o a l a t some node g u a r a n t e e s t h e d i s c o v e r y of a cbmplete path w i t h o u t any p a t h r e q u i r i n g more t h a n a s i m p l e t e s t a t t h e c o r r e s p o n d i n g node i n t h e graph a s each l i n k is added t o t h e p a t h . m a t i s needed f o r s i t u a t i o n r e c o g n i t i o n i n a g e n e r a l i z a t i o n of Q u i l l i a n ' s s e m a n t i c i n t e r s e c t i o n t e c h n i q u e i n which t h e s o u r c e and g o a l nodes a r e r e p l a c e d by a p~t e n t i a l l y l a r g e number of c o n c e p t nodes, some of which a r e s t i m u l a t e d by immediate i n p u t , and some of which a r e remember i n g r e c e n t a c t i v a t i o n i n t h e p a s t .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "The u s e of t h e g r a p h s t r u c t u r e i t s e l f t o hold marks is t h u s c r i t i c a l t o g a i n i n g a d v a n t a g e from t h i s a l g o r ithm. E s s e n t i a l l y , t h e nodes of t h e graph s e r v e a s rendezvous poiants where p a t h s t h a t a r e c o m p a t i b l e can meet each o t h e r .",
                "sec_num": null
            },
            {
                "text": "RecentAx ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Moreover , what is s i g n i f i c a n i i s n o t j u s t s i m p l e p a t h s between two nodes, b u t t h e c o n f l u e n c e of marks frpm mu1 t i p l e s o u r c e s i n predetermined p a t t e r n s . Moreover, u n l i k e Q u i l l i a n , who c o n s i d e r e d a l l c o n n e c t i o n s i d e n t i c a l l y i n s e a r c h i n g f o r p a t h s , w e w i l l c o n s l d e r marker p a s s i n g s t r a t e g i e s i n which marks can' be passed s e l e c t i v e l y a l o n g c e r t a i n l i n k s .",
                "sec_num": null
            },
            {
                "text": "A s a n example of t h e s i t u a t i o n r e c o g n i t i o n p r o c e s s u s i n g mat k e r p r o p a g a t i o n i n a t a x o n o m i c l a t t i c e ; l e t us c o n s i d e r a s i m p l e c a s e of i n t e r p r e t i n g t h e i n t e n t of a s i m p l e E n g l i s h s e n t e n c e . u e s t would be p l a c e d i n t h e l a t t i c e i n s u c h a way t h a t a l l more g e n e r a l c o n c e p t s of which i t is a n i n s t a n c e would be a c t i v a t e d , and i n p a r t i c u l a r , t h e c o n c e p t of a r e q u e s t to d i s p l a y a g e o g r a p h i c a l r e g i o n would be a c t i v a t e d .",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "An Example",
                "sec_num": "7."
            },
            {
                "text": "The p a r s i n g o f t h e o r i g i n a l s e n t e n c e c a n e i t h e r be done by an ATN grammar, o r by a v e r s i o n of t h e taxonomic l a t t i c e j . t s e l f ( o n e t h a t c h a r a c t e r i z e s a t a m n o m y of s e n t e n c e t y p e s ) . Let u s assume h e r e t h a t it is done by a n ATN grammar t h a t is c l o s e l y c o u p l e d t o a taxonomic l a t t i c e , w i t h t h e A T N r e p r e s e n t i n g t h e s y n t a c t i c i n f o r m a t i o n a b o u t s e n t e n c e form and ) t h e taxonomic l a t t i c e r e p r e s e n t i n g gener-a1 s e m a n t i c i n f o r m a t i o n . As t h e ATN grammar p i c k s up c o n s t i t u e n t s o f t h e s e n t e n c e , i t r e a c h e s s t a t e s where i t m a k e s h y p o t h e s e s a b o u t t h e s y n t a c t i c r o l e s ' t h a t t h o s e c o n s t i t u e n t s p l a y i n t h e s e n t e n c e (e.g.. \" t h i ? is t h e s u b j e c t \" , \" t h i s is t h e v e r b w , etc.1-.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "An Example",
                "sec_num": "7."
            },
            {
                "text": "Such h y p o t h e s e s a r e t h e n e n t e r e d i n t d t h e l a t t i c e , where t h e y b e g i n t o a c t i v a t e t h e r e c o g n i t i o n c o n d i t i o n s of c o n c e p t s i n t h e network.",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "An Example",
                "sec_num": "7."
            },
            {
                "text": "For example, i n t h e taxonomic l a t t i c e t h e r e i s a c o n c e p t of a n i m p e r a t i v e s e n t e n c e whose s u b j e c t is t h e s y s t e m , whose v e r b is \"show\", whose ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "An Example",
                "sec_num": "7."
            }
        ],
        "back_matter": [
            {
                "text": "As t h e p a r s i n q p r o c e e d s , t h e ATN w i l l make a s s e r t i o n s about t h e s e n t e n c e . i t is b u i l d i n g up, and it w i l l n o t o n l y be b u i l d i n g up s y n t a c t i c r e p r e s e n t a t i o n s of c o n s t i t u e n t s of t h e s e n t e n c e , b u t a l s o be b u i l d i n g up r e p r e s e n t a t i o n s of p o s s i b l e meanings of t h o s e c o n s t i t u e n t s . I n p a r t i c u l a r , it w i l l be b u i l d i n g up a list of Qhose c o n c e p t s i n t h e l a t t i c e of which t h e c u r r e n t d o n s t i t u e n t may be a r e s t r i c t i o n o r ili'stance ahd a l i s t 0% t h e d a t t r -v a l u e . p a i r i n g s t h a t have been found s o f a r . In t h e example above, wnen t h e p a r s e r h a s parsed t h e i n i t i a l p o r t i o n of t h e s e n t e n c e \"show me\", it h a s b u i l t up i n i t s i n t e r n a l ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "annex",
                "sec_num": null
            },
            {
                "text": "network. R i e g e r , C . ( 1 9 7 7 ) \" S p o n t a n e o u s .Computation i n C o g n i t i v e Models,\" ",
                "cite_spans": [],
                "ref_spans": [],
                "eq_spans": [],
                "section": "Thus, t h e i n t e r s e c t i o n of f o o t p r i n t s from t h e v a r i o u s c o n s t i t u e n t s of t h e s e n t e n c e a < t h l s c o n c e p t node h a s s e r v e d t o s e l e c t t h i s node o u t o f a l l t h e o t h e r nodes i n t h e",
                "sec_num": null
            }
        ],
        "bib_entries": {},
        "ref_entries": {
            "FIGREF0": {
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                "text": "More s p e c i f i c s i t u a t i o n s might be: \" t r y i n g t o s c h e d u l e a m e e t i n g f o r t h r e e p e o p l e , two of which h a v e busy s c h e d u l e s n , \"about to p r i n t a message from a u s e r t o h i m s e l f n , \" a b o u t t o r e f e r t o a d a t e i n a r e c e n t p r e v i o u s y e a r i n a c o n t e x t where p r e c i s i o n b u t c o n c i s e n e s s is r e q u i r e d u . c e p t u a l taxonamy by t h e i n t e l l i g e n t machine w i l l be a t t e m p t s t o i d e n t ' i f y and a c t i v a t e t h o~e s i t u a t i o n d e s c r i p t i o n s -t h a t a p p l y t o i t s c u r r e n t s i t u a t i o n o s i d e r any g d v i c e t h a t may be s t o r e d t h e r e . N o t e ' t h a t \" c o n s i d e r i n g a d v i c e of t y p e Xn is i t s e l f an example of a s i t u a t i o n , s o t h a t t h i s p r o c e s s can e a s i l y become r e c u r s i v e and p o t e n t i a l l y unmanageable w i t h o u t a p p r o p r i a t e c a r e ."
            },
            "FIGREF1": {
                "num": null,
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                "type_str": "figure",
                "text": "s i t u a t i o n might be d e s c r i b e d , and it is n o t c l e a r how one s b u l d c o n s t r u c t such a d e s c r i p t i o n . Moreover, u n t i l it is s o r e c o g n i z e d , a s i t u a t i o n c o n s i s t s of a c o l l e c t i o n of u n r e l a t e d e v e n t s and c o n d i t i o n s . The p r o c e s s of r e c o g n i z i n g t h e e l e m e n t s c u r r d n & l y b e i n g p e r c e i v e d as an i n s t a n c o v e r i n g t h a t t h o s e elements c a n be i n t e r p r e t e d a u a t i o n d e s c r i p t i o n known t o t h e system."
            },
            "FIGREF2": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "p r o c e s s of c r e a t i n g a d e s c r i p t i o n of t h e c u r r e n t s i t u a t i o n is v e r y much l i k e t h e p r o c e s s of p a r s i n g a s e n t e n c e , and i n h e r e n t l y u s e s t h e knowledge s t r u c t u r e of t h e system l i k e a p a r s e r uses a grammar i n o r d e r t o c o n s t r u c t t h e appropr i a t e d e s c r i p t i o n ."
            },
            "FIGREF3": {
                "num": null,
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                "text": "s i t u a t i o n may be a r b i t r a r y (e.g. e v e n t s , p r e c e d i n g one a n o t h e r i n time, p e o p l e , p l a c e s , or p h y s i c a l objects i n v a r i o u s s p a t i a l r e l a t i o n s h i p s w i t h e a c h o t h e r , objects i n p h y s i c a l o r l e g a l p o s s e s s i o n of p e o p l e , p e o p l e , i n r e l a t i o n s h i p s o f a u t h o r i t y t o Other p e o p l e , e t c .) However, t h e b a s i c c h a r a c t e r i s t i c o f p a r s e r s , t h a t t h e o b j e c t s r e c o g n i z e d a r e c h a r a c t e r i z e d a s s t r u c t u r e d o b j e c t s assembled o u t o f r e c o g n i z a b l e p a r t s a c c o r d i n g t o known r u l e s of assembly, is s h a r e d by t h i s task o f s i t u a t i o n r e c o g n i t i o n . Note t h a t it is n o t s u f f i c i e n t m e r e l y t o c h a r a c t e r i z e a s i t u a t i o n as a member of one o f a f i n i t e number of known classes. That is, where it is n o t s u f f i c i e n t f o r a p a r s e r t o s i m p l y s a y t h a t i t s i n p u t is a n example o f a d e c l a r a t i v e s e n t e n c e ( o n e wants Zo ' b e able t o ask what t h e s u b j e c t i s , what t h e v e r b is, whether t h e s e n t e n c e h a s p a s t , p r e s e n t o r f u t u r e t e n s e , e t c . ) , i n a s i m i l a r way it 'is i n s u f f i c i e n t t o m e r e l y say t h a t an i n p u t s i t u a t i o n i s a n example of someone d o i n g something. One must g e n e r a t e a d e t a i l e d d e s c r i p t i o n o f who is d o i n g what t o whom, etc."
            },
            "FIGREF4": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "f i c i e n t t o c h a r a c t e r i z e a s i t u a t i o n as a s i n g l e i n s t a n c e of an e x i s t i n g c o n c e p t w i t h v a l u e s f i l l e d i n f c r empty, s l o t s .I n g e n e r a l , a s i t u a t i o n d e s c r i p t i o n must be ac o m p o s i t e s t r u c t u r e d object, v a r i o u s s u b p a r t s of which w i l l be i n s t a n c e s o f o t h p r c o n c e p t s assembled t o g e t h e r i n ways t h a t are f o r m a l p e r m i t t e d , i n much t h e same way t h z t h e d e s c r i p t i o n of a s e n t e n c e is p u t t o g e t h e r from i n s t a n c e s o f noun p h r a s e s , c l a u s e s , and p r e p o s i t i o n a l p h r a s e s . The s p e c i f i c i n s t a n c e b u i l t up must keep t r a c k o f which c o n s t i t u e n t s of t h e s p e c i f i c s i t u a t i o n f i l l which r o l e s of t h e c o n c e p t s b e i n g r e c o g n i z e d . Moreover, it c a n n o t do so by s i m p l y f i l l i n g i n t h e s l o t s o f t h o s e g e n e r a l c o n c e p t s , s i n c e a g e n e r a l c o n c e p t may have m u l t i p l e i n s t a n t i a t i o n s i n many s i + u a t i o n s . R a t h e r , new s t r u c t u r e s r e p r e s e n t i n g i n s t a n c e s of t h o s e c o n c e p t s must be c o n s t r u c t e d and p a i r i n g s o f c o n s t i t u e n t r o l e s from t h e c o n c e p t and role f i l l e r s from t h e c u r r e n t s i t u a t i o n must b e a s s o c i a t e d w i t h e a c h new i n s t a n c e ."
            },
            "FIGREF5": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "lhe Process of Situation Recognition The p r o c e s s of s i t u a t i o n r e c o g n i t i o n c o n s i s t s of d e t e c t i n g t h a t a s e t of p a r t i c i p a n t s of c e r t a i n k i n d s s t a n d i n some s p e c i f i e d r e l a t i o n s h i p t o e a c h o t h e r . I n g e n e r a l , when some set o f p a r t i c i p a n t s is p r e s e n t a t t h e s e n s o r y i n t e r f a c e of t h e s y s t e m (immediate' i n p u t p l u s p a s t memory) , t h e t a s k o f d e t e r m i n i n g whether t h e r e is some s i t u a t i o n d e s c r i p t i o n i n memor-y t h a t w i l l a c c o u n t f o r t h e s e l a t i o n s h i p s o f t h o s e i n p u t s is n o t t r i v i a l . I f t h e t o t a l number o f s i t u a t i o n d e s c r i p t i o n s i n t h e system i s s u f f i c i e n t l y small, a l l of them c a n be i n d i v i d u a l l y t e s t e d a g a i n s t t h e i n p u t to s e e i f any a r e s a t i s f i e d . I f t h f i c i e n t l y l a r g e , however, t h i s is no+ feasible."
            },
            "FIGREF6": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "A s a n example, c o n s i d e r t h e f o l l o w i n g fragment of a p r o t o c o l of a commander g i v i n g commands t o an i n t e l l i g e n t d i s p l a y system: Cdr: Show m e a d i s p l a y nf t h e e a s t e r n Mediterranean. [computer produces d i s p L a y ] Cdr : Focus i.n more on I s r a e l and Jordan. [computer d o e s s o ] Cdr : Not t h a t much; I want t o be a b l e t o s e e P o r t Said and t h e I s l a n d of Cyprus. I n t h e f i r s t , c l a u s e o E t h e t h i r d command of t h i s d i s c o u r s e , (i.e."
            },
            "FIGREF7": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "g g , e r e d by t h e ongoing d i s c c u r s e w i l l l e a v e traces of t h e i~, having f i r e d , s o t h a t c o i n c i d e n c e s o f such t r a c e s c a n be e f f i c i e n t l y d e t e c t e d ."
            },
            "FIGREF8": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "e s f o r i n t e r p r e t i n g t h e meanings of s e n t e n c e s were indexed a c c o r d i n g t o t h e v e r b of t h e s e n t e n c e and r u l e s f o r i n t e r p r e t i n g Roun p h r a s e s were indexed by t h e head noun. Although t h i s approach r e d u c e s t h e number o f r u l e s t h a t need t o be c o n s i d e r e d , it h a s s e v e r a l l i m i t a t i o n s s t i l l . The f i r s t is t h a t t h e r e may be some v a l u e s o f t h e index key f o r which t h e r e a r e s t i l l a l a r g e number of r u l e s t o c o n s i d e r . 'In t h e case of t h e LUNAR system, f o r example, t h e v e r b \"be\" had a l a r g e number of r u l e s t o a c c o u n t f o r d i f f e r e n t s e n s e s of t h e word. Another is t h a t t h e r e c a n be c e r t a i n c o n s t r u c t i o n s f o r which t h e r e is no s i n g l e e a s i l y d e t e c t e d f e a t u r e t h a t is s t r o n g l y c o n s t r a i n i n g a s t o p o s s i b l e meaning. I n t h i s c a s e , t h e r e is no u s e f u l index key t h a t c a n be used t o s e l e c t a s u f f i c i e n t l y c o n s t r a i n e d s e t of r u l e s t o t r y . Another l i m i t a t i o n Of t h i s i n d e x i n g a p p r~c h a s t h e range of language becomes more fl!uent i s t h a t i n c e r t a i n e l l i p t i c a l s e n t e n c e s , t h e c o n s t r a i n i n g key may be e l l i p s e d , and a l t h o u g h one can have t h e r u l e s indexed by o t h e r keys as w e l l , t h e remaining ones may n o t s u f f i c i e n t l y c o n s t r a i n t h e s e t of races t h a t need t o be c o n s i d e r e d . F i n a l l y , even when t h e s e t o f rule's h a s been c o n s t r a i n e d t o a r e l a t i v e l y s m a l l s e t , t h e r e is f r e q u e n t l y a good d e a l o f s h a r i n g of common t e s t s among d i f f e r e n t r u l e s , and c o n s i d e r i n g e a c h r u l e i n d e p e n d e n t l y r e s u l t s i n r e p e a t i n g t h e s e tests s e p a r a t e l y f o r each r u l e . One approach t o s o l v i n g -a l l of t h e above problems i s t o use what I have been c a l l i n g a I1factored knowledge s t r u c t u r e n f o r t h e r e c o g n i t i o n p r o c e s s . I n such a s t r u c t u r e , t h e common p a r t s o f d i f f e r e n t r u l e s are-merged s o t h a t th'e p r o c e s s o f t e s t i n g t h e m is done o n l y once. With such s t r u c t u r e s , one c a n e f f e c t i v e l y t e s t a l l o f t h e r u l e s i n a v e r y l a r g e s e t , and d o s o e f f i c i e n t l y , b u t never considek any s i n g l e r u l e i n d i v i d u a l l y . A t e a c h p o i n t i n a f a c t o r e d knowledge s t r u c t u r e , a t e s t is made and some i n f o r m a t i o n g a i n e d a b o u t tho i n p u t .The r e s u l t of t h i s t e s t d e t e r m i n e s t h e n e x t t e s t t o be made."
            },
            "FIGREF9": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "i t i o n a l i n f o r m a t i o n accumulated, t h e s e t of p o s s i b l er u l e s t h a t c o u l d be s a t i s f i e d by t h e i n p u t , g i v e n t h e v a l u e s of t h e t e s t s so f a r made, is g r a d u a l l y narrowed u n t i l e v e n t u a l l y o n l y r u l e s t h a t a c t u a l l y match t h e i n p u t remain. U n t i l t h e end ~f t h i s d e c i s i o n s t r u c t u r e is reached, however, none of t h e s e r u l e s is a c t u a l l y c o n s i d e r e d e x p l i c i t l y .T h i s pr i n c i p l e of f a c t o r i n g t o g e t h e r common p a r t s of d i f f e r e n t p a t t e r n s t o f a c i l i t a t e shared p r o c e s s i n g is t h e b a s i c t e c h n i q u e t h a t makes ATN grammars ,[Woods,   19701 more e f f i c i e n t i n some sense t h a n o r d i n a r y p h r a s e s t r u c t u r e grammars.I t h a s a l s o been used by t h e l e x i c a l r e t r i e v a l component of t h e BBN speech understanding system [Woods e t a 1 . , 1976; Wolf and Woods, 19771 and a c c o u n t s f o r t h e e f f i c i e n c p of t h e f i n l t e s t a t e grammar? approach of t h e CMU Harpy system [Lowerre, 19761. A r e c e n t i n n o v a t i v e u s e of t h i s p r i n c i p l e a p p e a r s i n R i e g e r t s \" t r i g g e r t r e e s \" f o r o r g a n i z i n g spontaneolls computations [ R i e g e r , 19771. Whethe? f a c t o r e d t o g e t h e r or n o t , t h e t a s k of accegsing r u l e s is n o t a s i m p l e one, One problem i s t h a t r u l e s d o n ' t match t h e i n p u t l e t t e r -f o r -l e t t e r : r a t h e r , they have v a r i a b l e s i n them w i t h v a r i o u s r e s t r i c t i o n s on what t h e y can match. For example a r i l e might s a y t h a t whenever an access i s made t o a c l a s s i f i e d f i l e , t h e n a record of t h e p e r s o n making t h e r e q u e s t should be made. Z'he d e s c r i p t i o n , \"ali a c c e s s t o a c l a s s i f i e d f i l e n needs t o be matched a g a i n s t t h e user8,s r e q u e s t ( o r some s u b p a r t o f it) and i n t h a t match, t h e d e s c r i p t i o n \" a c l a s s i f i e d f i l e n w i l l be matched a g a i n s t some s p e c i f i c f i l e name. I n this kind of s i t u a t i o n , t h e r e is rrr, n a t u r a l o r d e r i n g of t h e rules, analogous t o t h e a l p h a b e t i c a l o r d e r i n g of words, that w i l l h e l p i n f i n d i n g t h e r u l e s t h a t a r e satlsfled by the g i v e n s i t u a t i o n . Nor i s a s t r u c t u r e a s simple as t h e d i c t i o n a r y t r e e above adequate f o r t h i s c a s e ."
            },
            "FIGREF10": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "is made t o a t o p s e c r e t f i l e (more s p e c i f i c t h a n c l a s s i f i e d ) , t h e n check t h e need-to-know s t a t u s of t h e user for t h a t i n f o r m a t i o n and block a c c e s s i f n o t s a t i s f i e d \" . I n t h e case of a r e q u e s t t o a t o p s e c r e t f i l e , both of t h e above r u l e s must be found, w h i l e i n t h e c a s e of an o r d i n a r y c b s s i f i e d f i l e , only t h e f i r s t should. The a c t u a l i n p u t , however, b i l l n o t e x p l i c i t l y mention e i t h e r \" t o p -s e c r e t n o r \" c l a s s i f i e d n , b u t w i l l merely be some' f i"
            },
            "FIGREF11": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "h i s t e c h n i q u e would a l s o f i n d c h a i n s of i n d i r e c t c o n n e c t i o n s such a s \" P l a n t s can be food f o r people\" and \"People draw nourishment from food,\" The method was c a p a b l e of f i n d i n g p a t h s of a r b i t r a r y length. The problem of f i n d i n g c o n n e c t i o n s between c o n c e p t s i n a knowledge network is l i k e t h e problem of f i n d i n g a p a t h through a maze from a s o u r c e node tb some goal node. A t t h e lowest l e v e l , i t r e q u i r e s a t f ' i a l and e r r o r s e a r c h i n a s p a c e t h a t can be l a r g e and p o t e n t i a l l y c o m b i n a t o r i c . That is, i f one element of t h e i n p u t c o u l d be connected t o k d i f f e r e n t c o n c e p t s , each of which would i n t u r n be connected t o k o t h e r s , and s o on, u n t i l f i n a l l y a c o n c e p t t h a t connected to t h e g o a l was d i s c o v e r e d , t h e n t h e space i n which one would have t o s e a r c h t o f i n d a p a t h of l e n g t h n would m n t a i n k n p a t h s . However, i f one s t a r t e c t i o n ) , one could f i n d a l l t h e p a t h s of 1 g t h n/2 from e i t h e r end i n o n l y nP9 e n had a n e f f i c i e n t way t o d e t e r m i n e whether any of t h e p a t h s from t h e s o u r c e node connected w i t h any of t h e paths from t h e -g o a l node, such s e a r c h from b o t h ends would have a c o n s i d e r a b"
            },
            "FIGREF12": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "s e n t e d some s n t e r e s t i n qformal machine s p e c i f i c a t i o n s of Q u i l l i a n -t y p e s p r e a d i n g a c t i v a t i o n p r o c e s s e s which have t h i s c h a r a c t e r i s t i c . 4, The Structure of Concepts 'In b u i l d i n g up i n t e r n a l d e s c r i p t i o n s of s i t u a t i o n s , o n e needs t o make use of c o n c e p t s of o b j e c t s , s u b s t a n c e s , times; p l a c e s , e v e n t s , c o n d i t i o n s , p r e d i c a t e s , f u n c t i o n s , i n d i v i d u a l s , e t c . Each such i n t e r n a l c o n c e p t w i l l i t s e l f have a s t r u c t u r e and c a n be r e p r e s e n t e d a s a c o n f i g u r a t i o n of a t t r i b d t e s o r p a r t s , s a t i s f y i n g c e r t a i n r e s t r i c t i o n s and s t a n d i n g i n s p e c i f i e d r e l a t i o n s h i p s t o e a c h o t h e r . Brachman [1978] h a s developed a s e t of e p i s t e m o l o g i c a l l y e x p l i c i t c o n v e n t i o n s f o r r e p r e s e n t i n g such c o n c e p t s i n a n S t r u c t u r e d I n h e r i t a n c e Network\", i n which i n t e r r e l a t i o n s h i p s of v a r i o u s c a r t s of c o n c e p t s t o each o t h e r and t o more g e n e r a l and more s p e c i f i c c o n c e p t s a r e e x p l i c i t l y r e p r e s e n t e d . The e s s e n t i a l c h a r a c t e r i s t i c of t h e s e networks is t h e i r a b i l i t y t o r 4 p r e s e n t d e s c r i p t i o n s of s t r u c t u r e d o b j e c t s of v a r i o u s d e g r e e s of g e n e r a l i t y w i t h e x p l i c i t r e p r e s e n t a t i o n of t r i b u t b p a r t , c o n s t i t u e n t , f e a t u r e , etc.) and a s e t of s t r u c t u r a l r d a t i o n s h i p s among them. Some of t h e s e d a t t r s are r e p r e s e n t e d d i r e c t l y a t a given node, and o t K e r s a r e i n h e r i t e d i n d i r e c t l y from o t h e r nodes i n t h e network t o which t h e y a r e r e l a t e d . L e t u s assume t h a t each c o n c e p t t h a t t h e system u n d e r s t a n d s is t e p r e s e n t e d a o n c e p t u a l taxonomy of a l l poSfiible n e n t i t i e s B 1 t h a t t h e system can p e r c e i v e o r understqnd. Each node i n t h i s taxonomy c a n be t h o u g h t of a s a m i c r o schema f o r t h e r e c o g n i t i o n of i n s t a n c e s of t h a t c o n c e p t . Each h a s a s e t of d a t t r s w i t h i n d i v i d u a l r e s t r i c t i o n s and a s e t of s t r u c t u r a l c o n d i t i o n s t h a t r e l a t e t h e d a t t r s t o one a n o t h e r . These r e s t r i c t i o n s and s t r u c t u r a l c o n d i t i o n s may t h e m s e l v e s be d e f i n e d i n terms of o t h e r c o n c e p f s d e f i n e d by o t h e r m i c r o schemata, and s o on u n t i l a l e v e l of p r i m i t i v e l y d e f i n e d , d i r e c t l y p e r c e i v a b l e c o n c e p t s is r e a c h e d . Each concept i n t h e taxonomy can be t h o u g h t of a s having a l e v e l o$ a b s t r a c t n e s s d e f i n e d as the maximum depth 9f n e s t i n g of i t s c o n s t i t u ' e n t s t r u c t u r e . I n s t a n c e s of p r i m i t i v e l y d e f i n e d c o n c e p t s have l e v e l 0 , c o n s t e l l a t i o n s of those c o n c e p t s have l e v e l 1, a c o n c e p t having l e v e l 1 and lower c o n c e p t s a s d a t t r s has l e v e l 2 , and s o on. c e p t s , t h e n the s i t u a t i o n r e c o g n i t i o n problem would be g r e a t l y s i m p l i f i e d , s i n c e one never needs t o r e c o g n i z e p o r t i o n s of t h e i n p u t as e n t i t i e s t h a t p a r t i c i p a t e a s c o n s t i t u e n t s of l a r g e r e n t i t i e s . The g e n e r a l problem, however, r e q u i r e s u s t o do e x a c t l y t h a t . More , s e r i o u s l y , t h e g e n e r a l c a s e r e q u i r e s u s t o r e c o g n i k e a c o n c e p t some of whose d a t t r s may have r e s t r i c t i o n s d e f i n e d i n terms of t h e c o n c e p t i t s e l f . This i s t r u e , f o r example, for t h e c o n c e p t of noun p h r a s e i n a taxonomy of s y n t a c t i c c o n s t r u c t i o n s . Such r e c u r s i v e l y d e f i n e d c o n c e p t s have no maximum l e v e l of a b s t r a c t n e s s , a l t h o u g h any g i v e n i n s t a f i c e w i l l o n l y i n v o l v e a f i n i t e number of l e v e l s ' of r e c u r s i o n . T h i s p o t e n t i a l f o r r e c u r s i v e d e f i n i t i o n m u s t be kept i n mind when f o r m u l a t i n g a l g o r i t h m s f o r s i t u a t i o n r e c o g n i t i o n ."
            },
            "FIGREF13": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "The Need for Inheritance StructuresAs a r e s u l t of havinq d i f f e r e n t l e v e l s of a b s t r a c f %on i n o n e ' s taxonomy, an i n p u t s i t u a t i o n w i l l o f t e n s a t i s f y s e v e r a l s i t u a t i o n d e s c r i p t i o n s s i m u l t a n e o u s l y , no o n 6 of which w i l l a c c o u n t f o r a l l of t h e i n p u t nor s u p p l a n t t h e r e l e 5 a n c e of t h e o t h e r s . For example, a u l t a n e o u s l y an example of changing ad i s p l a y and of d i s p l a y i n g a s h i p . Advice f o r b o t h a c t i v i t i e s d u s t be c o n s i d e r e d . Moreover, a s i n g l e d e s c r i p t i o n may Rave s e v e a l d i f f er e n t i n s t a n t i a 0 t i o g s i nt h e c u r r e n t s i t u a t i o n , w i t h s i t u a t i o n d e s c r i p t i o n s becdming a r b i t r a r i l y complex by t h e a d d i t i o n of v a r i o u s q u a l i f i e r s , by t h e c o n j u n c t i o n and d i s j u n c t i o n of d e s c r i p t i o n s , e t c . For exarnple, one might want t o s t o r e a d v i c e a s s o c i a t e d w i t h t h e s i t u a t i o n [wanting t o d i s p l a y a .large s h i p a t a l o c a t i o n on t h e s c r e e n t h a t 1s w i t h i n one u n i t d i s t a n c e fram e i t h e r t h e t o p , bottom, o r side of t h e s c r e e n when t h e s c a l e of t h e d i s p l a y is g r e a t e r than 1:1000].F i n a l l y , s i t u a t i o n descriptions may subsume o t h e r d e s c r i p t i o n s a t lower l e v e l s of d e t a i l , and a d v i c e from both may be r e l e v a n t and may e~t h e r supplement or c o n t r a d i c t each o t h e r .For example, d i s p l a y i n g an a i r c r a f t c a r r i e r is a s p e c i a l c a s e of d i s p l a y i n g a s h i p , and t h e r e may be s p e c i f i c a d v i c e a s s o c i a t e d with d i s p l a y i n g c a r r i e r s a s well a s more g e n e r a l a d v i c e f o r d i s p l a y i n g any s h i p . Thus, c o n v e n t i o n s w i l l be r e q u i r e d t o determine which a d v i c e t a k e s precedence over t h e o t h e r i f c o n f l i c t s a r i s e . The or,ganization of l a r g e numbers of such s i t u a f i o n d e s c r i p t i o n s of varying d e g r e e s of g e n e r a l i t y s o t h a t a l l d e s c r i p t i o n s more g e ne r a l or hoxe s p e c i f i c t h a n a g i v e n one can e f f i c i e n t l y be found is one t h i n g w e r e q u i r e of an i n t e l l i g e n t cornputer a s s i s t a n t .I n o r d e r t o b u i l d and m a i n t a i n such a s t r u c t u r e , it is important t o s t o r e each r u l e a t t h e a p p r o p r i a t e l e v e l of g e n e r a l i t y , r e l y i n g on a mechanism whereby more s p e c i f l c s i t u a t i o n s a u t o m a t i c a l l y i n h e r i t i n f o r m a t i o n from more g e n e r a l ones. That i s , when one wants t o c r e a t e a s i t u a t i o n d e s c r i p t i o n t h a t is more s p e c i E i c t h a n a given one i n some dimension, one does n o t want t o have t o copy a l l of t h e a t t r i b u t e s of t h e g e n e r a l s i t u a t i o n , but o n l y t h o s e t h a t a r e changed. Aside from conserving memory s t o r a g e , avoiding such copying a l s o f a c i l i t a t e s updating and m a i n t a i n i n g t h e c o n s i s t e n c y of t h e d a t a b a s e by a v o i d i n g t h e c r e a t i o n of d u p l i c a t e c o p l e s of i n f o r m a t i o n t h a t then may need t o be i n d e p e n d e n t l y modified and could a c c i d e n t a l l y be modified i n c o n s i s t e n t l y . For example, one may want t o s t o r e a d v i c e a b o u t d i s p l a y i n q g e o g r a p h i c a l f e a t u r e s , about d i s p l a y i n g such f e a t u r e s t h a t cover an a r e a , a b o u t d i s p l a y i n g b o d i e s of w a t e r , a b o u t d i s p l a y i n g l a k e s , e t c . Thus, information a b o u t f i n d i n g t h e a r e a covered by a f e a t u r e would be s t o r e d a t t h e l e v e l of d e a l i n g with such area-cover ing f e a t u r e s . i n f oxmat i o n about d i s p l a y i n g water inqa c e r t a i n c o l o r would be s t o r e d a t t h e l e v e l of d i s p l a y i n g bod,les of w a t e r , and i n f o r m a t i o n a b o u t having i n l e t s and o u t l e t s would be s t o r e d a t t h e l z v e l of l a k e s . I n any s p e c i f i c s i t u a t i o d t h a t t h e system f i n d s i t s e l f , many such Concepts a t d i f f e r e n t l e v e l s of g e n e r a l i t y w i l l be s a t i s f i e d , and t h e a d v i c e a s s o c i a t e d with a l l of bhem becorna p p l i c a b l e . That is, any more s p e c i f i c c o n c e p t , i n c l u d i n g t h a t of t h e c u r r e n t situation, rnherlts a g r e a t d e a l of i n f o r m a t i o n t h a t is e x p l i c i t l y s t o r e d a t h i g h e r l e v e l s i n t h e taxonomy. c r i p t i o n s t h a t we a r e d e a l i n g w i t h , even t h e s p e c i f i c a t i o n of what d a t t r s -a given c o n c e p t p o s s e s s e s 1s skored a t t h e most g e n e r a l l e v e l and i n h e r i t e d by more spec i f ic c o n c e p t s . n u s , f o r examp,le , the d e s c r i p t i o n s of 3 t t r i b u t e d a t t t s f o r c o l o r and weight a r e s t o r e d f o r a g e n e r a l c o n c e p t of p h y s i c a l o b j e c t . These d a t t r s a r e then i n h e r i t e d by any more specific c o n c e p t s of p h y s i c a l o b j e c t s , such a s p l a n e s , s h i p s , desks, and p e n c i l s . 6 . lhe Taxonomic Lattice I b e l i e v e t h a t a g e n e r a l s o l u t i o n t o the s~t u a t i o n r e c o g n i t i o n problem can be o b t a i n e d by t h e use of a c l a s s i f i c a t i o n s t r u c t u r e i n which t r a c e s of i n d i v i d u a l elements of complex c o n c e p t s can i n t e r s e o n n e c t i o n s t h a t may n o t be s t r o n g l y i n f e r a b l e ,from c o n s t r a i n i n g e x p e c t a t i o n s . The s t r u c t u r e t h a t I propose t o use is a v e r s i o n of Brachman's s t r u c t u r e d i n h e r i t a n c e networks, i n which d e s c r i p t i o n s of a l l p o t e n t i a l l y r e l e v a n t s i t u a t i o n s a r e s t o r e d w i t h e x p d i c i t i n d i c a t i o n s of g e n e r a l subsumpkion.of one s i t u a t i o n by a n o t h e r , and ex p l i c i t i n d i c a t i o n s of t h e i n h e r i t a n c e of d a t t r s and of a d v i c e by one c o n c e p t from a n o t h e r . This s t r u c t u r e , whlch I have c a l l e d a taxonomic l a t t i c e , i s c h n a c t e r i z e d by a m u l t i t u d e of s i t u a t i o n d e s c r i p t i o n s a t d i f f e r e n t l e v e l s of g e n e r a l i t y .W e s a y t h a t a s i t u a t i . o n d e s c r i p t i o n S 1 subsumes a d e s c r i p t i o n S 2 i f any s i t u ? t l o n s a t i s f y i n g S2 w i l l a l s o s a t i s f y S l . I n t h i s c a s e , S1 is a more g e n e r a l d e s c r i p t i o n t h a n S 2 , and is p l a c e d h i g h e r i n t h e taxonomy. For example, [ d i s p l a y i n g a p o r t i o n of c o u n t r y ] i s a more s p e c i f i c s i t u a t i o n t h a n [ d i s p l a y i n g a g e o g r a p h i c a l a r e a ] , which is i n t u r n more s p e c i f i c than [ d i s p l a y i n g a d i s p l a y a b l e e n t i t y ] . A l l Of t h e s e a r e subsumed by a g e n e r a l concept [ p u r p o s i v e a c t i v i t y ] , wh-ich i n t u r n is more s p e c i f i c t h a n [ a c t i v i t y ] . Moreover, a g i v e q d e s c r i p t i o n can subsume many incomparable d e s c r i p t i o n s an4 can i t s e l f be subsumed by many incomparable d e s c r i p t i o n s . For example, an i n s t a n c e of [ d i s p l a y i n g a g e o g r a p h i c a l a r e a ] i s a l s o an i n s t a n c e of [ a c c e s s i n g a g e o g r a p h i c a l a r e a ] , [ d i s p l a y i n g . i n f o r m a t i o n ] , and [ u s i n g t h e d i s p l a y ] , and may p o s s i b l y a l s o be an i n s t a n c e of [ r e s p o n d i n g t o a user comma~~d] . The s p a c e of p o s s i b l e situation d e s c r i p t i o n s forms a l a t t i c e under t h e r e l a t i o n of subsumption. A t t h e t o p of t h e l a t t i c e is a s i n g l e , most g e n e r a l s i t u a t i o n we w i l l c a l l T, which is always s a t i s f i e d and can be t h o u g h t of a s t h e d i s j u n c t i o n of a l l p o s s i b l e s i t u a t i o n s . Anything t h a t is u n i v e r s a l l y t r u e can be s t o r e d h e r e . Conversely, a t t h e bottom of t h e l a t t i c e is a s i t u a t i o n t k a t i s nevef s a t i s f i e d , which w e c a l l N I L ; I t c a n be khought of a s t h e c o n j u n c t i o n o f a l l p o s s i b l e ( i n c l u d i n g i n c o n s i s t e n t ) s i t u a t i o n s . Assert i o n s of n e g a t i v e e x i s t e n c e c a n be s t o r e d h e r e . A t t h e \"middle\" l e v e l of t h e l a f t i c e a r e a s e t of p r i m i t i v e p e r c e p t i b l e p r e d i c a t e s -d e s c r i p t i o n s whose t r u t h i n t h e w o r l d a r e d i r e c t l y m e a s u t a b l e by t h e \" s e n s e organs'' of t h e s y s t e m . A l l classes above t h i s l e v e l a r e constructed by some form of g e n e r a l i z a t i o n o p e r a t e o n , and a l l c l a s s e s below a r e formed by some form of s p e c i a l i z a t i o n . f i c i e n t l y low i n t h e l a t t l c e , o n e c a n b e g i n t o fgrm i n c o n s i s t e n t d e s c r i p t i o n s by t h e c o n j u n c t i o n of i n c q p a t i b l e c o n c e p t s , t h e i m p o s i t i o n of i m p o s s i b l e r e s t r i c t i o n s , e t c . ,There is n o t h i n g t o p r e v e n t s u c h c o n c e p t s from b e i n g formed; i n d e e d , i t is n e c e s s a r y i n o r d e r f o r t h e o r g a n i s m t o c o n t e m p l a t e , s t o r e , and remember t h e i r i n c o n s i s t e n c y . There a r e a number of s p e c i f i c r e l a t i o n s h i p s t h a t c a n c a u s e one s i t u a t i o n d e s c r i p t i o n t o subsume a n o t h e r . A g i v e n s i t u a t i o n d e s c r i p t i o n c a n be made more g e n e r a l t e l a x i n g a c o n d i t i o n on a d a t t r , by e l i m i n a t i n g t h e r e q u i r e m e n t f o r a d a t t r , by r e l a x i n g t h e c o n s t r a i n t s of i l i c i t l y d i s j o i n i n g i t ( o r ' i n g i t ) w i t h a n o t h e r d e s c r i p t i o n . A g i v e n d e s c r i p t i o n c a n be made more s p e c i f i c by t i g h t e n i n g t h e c o n d i t i o n s on a d d t t r , by a d d i n g a d a t t r , by t i g h t e n i n g t h e c o n s t r a i n t s of i t s s t r u c t u r a l d e s c r i p t i o n , o r by e x p l i c i t l y c o n j a l -n i n g ( a n d 1 i n g ) i t w i t h a n o t h e r d e s c r i p t i o n . These o p e r a t i o n s a p p l i e d t o any f i n i t e s e t of s i t u a t i o n d e s c r i p t i o n s i n d u c e a l a t t i c e s t r u c t u r e of p o s s i b l e s i t u a t i o n d e s c r i p f i o n s t h a t c a n be formed by c o m b i n a t i o n s of t h e e l e m e n t s of t h e , i n i t i a l s e t . We r e f e r t o t h i s s t r u c t u r e a s t h e v i r t u a l l a t t i c e i n d u c e d by a g i v e n s e t of s i t u a t i o n d e s c r i p t i o n s . Note t h a t o n l y a f i n i t e p o r t i o n of t h i s l a t t i c e need be s t o r e d w i t h e x p l i c i t c o n n e c t i o n s from more s p e c i f i c t o more g e n e r a l w n c e p t s . By p r o c e s s i n g thise x p l i c i t l a -t t i c e , o n e c a n t e s t a n y g i v e n d e s c r i p t i o n f o r membe\"rship i n the v i r t u a l l a t t i c e .and a s s i m i l a t e a n y new s i t u a t i o n d e s c r i p t i o n i n t o t h e e x p l i c i t l a t t i c e i n t h e a p p r o p r i a t e p l a c e c o r r e s p o i d i n g t o i t s p o s i t i o n i n t h e v i r t u a l l a t t i c e . c r i p t i o n a b o u t which i n f o r m a t i o n i s e x p l i c i t l y s t o r e d w i l l be e n t e r e d i n t o t h e e x p l i c i t l a t t i c e . Any s i t u a t i o n t h a t t h e machine c a n u n d e r s t a n d is i n some s e n s e a l r e a d y i n t h e v i r t u a l l a t t i c e and n e e d s o n l y be \" l o o k e d up\" i n i t . One t a s k we have i c i e n t a l g o r i t h m s t o tell whether a g i v e n s i t u a t i o n c a nbe u n d e r s t o o d i n t e r m s of t h e c o n c e p t s of t h e l a t t i c e and i f s o , t o c o n s t r u c t i t s c o r r e s p o n d i n g d e s c r i p t i o n and e x p l i c i t l y r e c o r d i k s r e l a t i o n s \u20ac 0 o t h e r c o n c e p t s i n t h e e x p l i c i t l a t t i c e ."
            },
            "FIGREF14": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "The example c h o s e n is n o t complex enough t o r e q u i r e a l l of the m a c h i n e f y d i s c u s s e d , b u t is p r e s e n t e d h e r e t o i l l u s t r a t e t h e mechanism. me m a j o r f e a t u r e s o f t h e s i t u a t i o n r e c o g h i t i o n mechanism o n l y become c r i t i c a l i n i n t e r p r e t i n g commands t h a t r e q u i r e s e v e r a l S e n t e n c e s t o b u i l d up, o r which depend on t h e c u r r e n t c o n t e x t i n complew ways, b u t s u c h s i t u a t i o n s a r e d i f f i c u l t t o i l l u s t r a t e . For o u r example, s u p p o s e t h a t t h e s y s t e m c o n t a i n e d a c0ncep.t f o r r e q u e s t s t o d i s p l a y a g e o g r a p h i c a l r e g i o n , and t h e u s e r ' s i n p u t r e q u e s t were \"Show m e t h e e a s t e r f i end of t h e M e d i t e r r a n e a n . \" The c o n c e p t [ r e q u e s t ] c o n t a i n s d a t t r s f o r t h e r e q u e s t o r , t h e r e q u e s t e e , a d e s c r i p t i o n of t h e s t a t e t h a t t h e r e q u e s t o r d e s i r e s , a form of r e q u e s t (demand, o r d e r , p o l i t e r e q u e s t , e x p r e s s i o n of p r e f e r e n c e , e t c . ) , and p e r b p s o t h e r s , Requests, c a n t a k e many f o r m s . Assume t h a t w e have s t o r e d i n t h e s y s t e m a r u l e t h a t s a y s \"Any s e n t e n c e of t h e form: 'show m e N P 1 is a r e q u e s t t o d i s p l a y t h a t NP.\" T h i s r u l e c o u l d be s t o r e d i n t h e l a t t i c e a s a p i e c e of a d v i c e a s s o c i a t e d w i t h t h e c o n c e p t \" A s e n t e n c e o f t h e form: 'show m e N P ' ,\" i n s u c h a way t h a t when a s e n t e n c e of t h e i n d i c a t e d form was f o u n d , an i n s t a n c e of a d i s p l a y r e q u e s t would be c r e a t e d . A t t h a t p o i n t , t h i s r e s u l t i n g d i s p l a y r e q"
            },
            "FIGREF15": {
                "num": null,
                "uris": null,
                "type_str": "figure",
                "text": "i n d i r e c t a b j e c t is t h e u s e r and whose d i r e c t o b j e c t is a d i s p l a y a b l e o b j e c t ."
            }
        }
    }
}