docs/reader-specification.md

Reader Specification v0.1 — uscogdata corpus contract

Language-neutral contract that any compliant reader for the uscogdata corpus must implement. The R package uscogdata is the reference implementation; future Python/Go/etc. ports implement the same contract.

1. Corpus layout

Published under a Nextcloud-hosted root (URL in USCOGDATA_URL env var), and mirrored to the public Hugging Face dataset civilytics/us-cog-finance (hf:// reads / bulk access; not in the live API's read path). Both surfaces mirror the same publish tree. The published year floor is FY1967 (the full legacy series; config.yml publish_min_year). As-of-year county (fips_county_asof) is NA for a small set of pre-2012-dissolved geographies catalogued in data/dissolved_geographies.csv (Nansemond VA→Suffolk 1974, etc.); present-geography fips_state/fips_county are always populated. The root contains:

manifest.json
data/
  long/
    year=1967/part-0.parquet
    year=1970/part-0.parquet
    ...
    year=2023/part-0.parquet
  canonical_fips_xwalk.parquet
  canonical_alias.parquet
  summary_categories.parquet
docs/
  README.md
  data_dictionary.md
  series_breaks.md
  reader-specification.md

manifest.json is the authoritative index. Readers MUST validate it on session open.

1.1. Year=2012 is modern-source only

The year=2012/part-0.parquet partition contains rows from the modern Individual Unit Files (Fin_GID_2012.txt + 2012FinEstDAT_*_pu.txt) only. Legacy wide-format 2012 content is deliberately excluded from the published corpus to preserve the invariant that no partition mixes the two source families. Readers can therefore treat any year as a single-source partition and never need to de-duplicate.

The pipeline retains the legacy 2012 long frame as an internal fixture for cross-era validation (it is used by validate_2012_dual_format / compare_2012_boundary to prove that the modern↔legacy crosswalks line up), but it is not part of the published artifacts.

2. manifest.json schema (schema_version = 6)

{
  "schema_version": 6,
  "built_at": "2026-07-22T...",
  "pipeline_commit": "<short-sha>",
  "data_vintage": {
    "source_vintages": { "...": "per-source vintage stamps from the registry" },
    "registry_rows": 0,
    "acs_vintage": "..."
  },
  "scope": {
    "gov_types_included": [0, 1, 2, 3],
    "gov_types_excluded": [4, 5],
    "scope_note": "v0.1: state, county, municipal, township only"
  },
  "schema": {
    "long_column_count": 28,
    "long_columns": ["fips_state", ...],
    "data_dictionary": "docs/data_dictionary.md"
  },
  "files": {
    "long_partitions": [
      {"year": 1967, "path": "data/long/year=1967/part-0.parquet",
       "sha256": "...", "row_count": 12345, "size_bytes": 98765}
    ],
    "metadata": [
      {"path": "data/canonical_fips_xwalk.parquet", "sha256": "...", "description": "..."},
      {"path": "data/canonical_alias.parquet", "sha256": "...", "description": "..."},
      {"path": "data/summary_categories.parquet", "sha256": "...", "description": "..."}
    ]
  },
  "series_breaks_ref": "docs/series_breaks.md",
  "reader_spec_ref": "docs/reader-specification.md"
}

3. Long parquet schema (28 columns)

See docs/data_dictionary.md § "Long parquet columns (28-column schema v6)" for full per-column documentation. Column order is authoritative; readers SHOULD NOT rely on positional indexing but MUST accept all 28 columns.

Schema v6 (2026-07-21) — BREAKING changes vs v5/v4. Two kinds:

1. Rename (fails loudly): fips_state_code → fips_state_asof, fips_county_code → fips_county_asof (same as-of-year meaning, clearer name). A consumer selecting the old names errors on a missing column.
2. Same name, CHANGED MEANING (silent): fips_state / fips_county are now the present/harmonized geography (each government's current county identity carried back to every year, derived from canonical_govid), NOT the as-of-year value they held under v4/v5. A join or filter on these won't error — it returns present-geography values on historical rows. Use fips_state_asof / fips_county_asof for as-of-year geography, and cog_legacy_state / cog_legacy_county for the raw GOVS source codes.

v4→v5 added harmonized_code and survey_weight (24→26); v5→v6 renamed the two _code columns and inserted cog_legacy_state/cog_legacy_county (26→28).

#	Column	Type	Notes
1	fips_state	integer	Present/harmonized 2-digit FIPS state (from canonical_govid 1–2), carried back to every year
2	type	integer	0=State 1=County 2=Muni 3=Township 4=SplDist 5=ISD
3	fips_county	integer	Present/harmonized FIPS county (from canonical_govid 4–6); 0/NA for states. Auto-handles renames/splits
4	govid	character	Census internal unit ID
5	gov_blank	character	Reserved Census field
6	gov_name	character	Government name
7	county_name	character	County name
8	fips_state_asof	integer	As-of-year FIPS state (renamed from fips_state_code)
9	fips_county_asof	integer	As-of-year FIPS county (renamed from fips_county_code); legacy from the GOVS→FIPS crosswalk, modern from source
10	cog_legacy_state	integer	Raw GOVS state code. Populated FY1967/1970–2016; NA FY2017+
11	cog_legacy_county	integer	Raw GOVS county code. Populated FY1967/1970–2016; NA FY2017+
12	fips_place_code	character	Place FIPS code
13	population	numeric	Population
14	popyear	integer	Year of population estimate
15	enrollment	numeric	School enrollment
16	enrollyear	integer	Year of enrollment estimate
17	function_code	character	Census function code
18	sch_level_code	character	School level code
19	fiscal_year_end	character	Fiscal year end date
20	srvy_year	integer	Survey year
21	item_code	character	Finance item code (e.g. T01, E62)
22	amt	numeric	Amount in $1,000s
23	srv_data	character	Survey data flag
24	impute_flag	character	Imputation flag
25	is_aggregate	logical	TRUE if row is a subtotal aggregate
26	canonical_govid	character	Stable 12-char canonical ID (PID census_id frozen at FY2023 vintage; 9xxxxx-unit corpus-assigned ids for governments never observed 2017+). See docs/data_dictionary.md § col 26 / docs/ids_reference.md § "Canonical namespace (Phase P)".
27	harmonized_code	character	Cross-vintage comparable item code; NA on aggregate rows
28	survey_weight	numeric	Legacy IndFin Weight (informational only — never aggregate with it); NA for modern-source rows

3.1 Spending concepts: Direct, Total, and the M-code

For each spending function the corpus publishes one flavor: Direct — a government's own spending (its E/F/G leaves), carried in the legacy era as the per-function family aggregate (-NN, e.g. -05) and in the modern era as the leaves themselves. Census's Total concept is Direct + M-code + L-code (the function's intergovernmental payments to local governments, e.g. M05, plus to state governments, e.g. L05). The identity Total = Direct + M + L holds arithmetically, and both code families are published in both eras — but "published" does not mean "sitting on a leaf row a reader can sum directly." In the legacy era (≤ FY2011) several IG code families — M05, M12, M47, M89, L47, L89 — are published only as is_aggregate = TRUE rows, because the wide source files expose those families only as aggregates; their leaves first appear in the modern era. Measured on the published corpus: in FY2007 only 26.3% of intergovernmental dollars sit on non-aggregate rows (129,835,142 of 493,510,366). M12 alone is 291,293,845 that year — 59% of the year's IG total — and is is_aggregate = TRUE, as are M89, M47, and L--. A reader that honors the NOT is_aggregate rule in §4 and then tries to reconstruct Total by summing M/L leaves out of spending_long therefore sees only a minority of legacy IG dollars and computes a "Total" that is silently ≈ Direct. Total must instead be assembled year-scoped, the way ige_local_m47_wide, ige_local_m89_wide, ige_state_l47_wide, ige_state_l89_wide, and corrections_ig_local_combined already do (see data_dictionary.md for the recipe-level detail) — it cannot inherit the basis views' leaf-only filter. L is identically 0 for state governments, so for a state Total = Direct + M — but L is material for local governments (91.6% of M for counties, 188.3% for cities) and must not be dropped.

A compliant reader MUST resolve "total spending" to the right concept per query shape — the dividing line is whether the query sums across governments:

Query shape	Concept	Rule
One government (or its own trend)	Direct or Total, consistently	either is valid; do not mix concepts across years
Any aggregation across governments	Direct only	summing Total double-counts intergovernmental flows (a grant is in the payer's Total and again in the recipient's Direct)

Worked identity (Alabama state government, corrections, FY2007, $1,000s): -05 (Direct) = E05+F05+G05 = 487,175; + M05 (27,210) + L05 (0) = 514,385 (Total). Alabama is a state, so L05 is 0; for a city or county the L term is material and must be included. Full explanation, the modern-era leaf caveat, and query examples: data_dictionary.md § "Total spending".

4. Required DuckDB views

A compliant reader registers these views on session open (pseudocode using the Nextcloud public share URL pattern):

long — raw unfiltered data

CREATE OR REPLACE VIEW long AS
SELECT * FROM read_parquet(
  '{USCOGDATA_URL}/data/long/**/*.parquet',
  hive_partitioning = true
);

spending_long — spending codes only

CREATE OR REPLACE VIEW spending_long AS
SELECT * FROM long
WHERE LEFT(item_code, 1) IN ('E', 'F', 'G', 'K')
  AND NOT is_aggregate;

revenue_long — revenue codes only

CREATE OR REPLACE VIEW revenue_long AS
SELECT * FROM long
WHERE LEFT(item_code, 1) IN ('T', 'A', 'B', 'C', 'D', 'U')
  AND NOT is_aggregate;

Readers MUST exclude is_aggregate = TRUE rows from all sum operations.

This rule is exactly right for Direct — spending_long/revenue_long are Direct-only views by construction. It does NOT mean a legacy-era Total can be reconstructed by summing M/L leaves out of these views: per §3.1, several IG code families are aggregate-only before FY2012, so a naive leaf-only sum silently collapses toward Direct instead of Total. A reader offering Total must assemble it year-scoped, per §3.1, not by relaxing this filter.

5. Verb contracts (uscogdata MVP)

⚠️ This section is the ORIGINAL design contract and has diverged from the shipped uscogdata package. The verbs below (cog_govs, cog_long, cog_summary) were never exported. The package's actual public API (see uscogdata's NAMESPACE) is: cog_open/cog_mirror, cog_spending, cog_revenue, cog_categories, cog_recipes, cog_gov_search, cog_find_peers, cog_peer_compare, cog_geographic_rollup, cog_basket_resolution, cog_basket_unresolved, cog_explain, cog_manifest. Treat the contracts below as design intent; consult the package's own function docs for the current signatures. A full rewrite of this section to the shipped API is tracked with the user-surface work in issue #42 / uscogdata#6.

cog_open

Opens a DuckDB connection to the corpus.

Inputs:

• url (character, default Sys.getenv("USCOGDATA_URL")) — Nextcloud share root

Side effects:

• Downloads/caches manifest.json
• Validates schema_version == 6
• Validates scope.gov_types_included covers expected types
• Registers 15 DuckDB views from the shipped .sql files (long; spending_long/revenue_long and their _harmonized variants; the canonical_fips_xwalk, summary_categories, gov_population_yearly, harmonization_map, harmonization_recipes, series_breaks_pq reference views; and the *_annotated / *_annotated_harmonized views). The harmonization/annotated-harmonized views are skipped when schema_version < 5.
• Sets session-global connection

Output: Connection object (invisibly)

cog_govs

Returns the canonical government registry.

Inputs:

• con — connection from cog_open
• types (integer vector, default 0:3) — gov_types to include
• name_pattern (character, default NULL) — regex filter on gov_name

Output columns: canonical_govid, gov_name, type, fips_state, fips_county, fips_place_code, acs_pop

cog_long

Returns raw long data (thin wrapper over the long view).

Inputs:

• con — connection
• govids (character vector, default NULL = all in scope)
• years (integer vector, default all available)
• item_codes (character vector, default NULL = all)
• include_aggregates (logical, default FALSE)

Output: tibble with 28 columns matching the long parquet schema.

cog_spending

Returns summarized spending by category.

Inputs:

• con — connection
• govids (character vector)
• years (integer vector)
• category (character vector, default NULL = all)
• spend_subtype (character "operations" | "capital" | NULL)
• per_capita (logical, default FALSE)
• adjust_to_year (integer, default NULL)

Output columns: year, canonical_govid, gov_name, spend_subtype, category, amt_nominal, [amt_real], [amt_per_capita_nominal], [amt_per_capita_real], codes_included, aggregate_fallback, notes

One row per (year × canonical_govid × spend_subtype × category). Real/per-capita columns only present when corresponding flag is set.

cog_revenue

Mirror of cog_spending for revenue categories.

Inputs/output: Same structure; revenue_subtype ∈ {own_source, federal, state, local_aid} replaces spend_subtype.

cog_summary

Cross-year totals, one row per (canonical_govid × category).

Inputs:

• con — connection
• govids (character vector)
• years (integer vector)
• categories (character vector, default all)
• per_capita (logical, default FALSE)

Output columns: canonical_govid, gov_name, category, and one {year} column per requested year.

cog_mirror

Downloads the full corpus to a local directory for offline use.

Inputs:

• con — connection
• dest_dir (character)
• overwrite (logical, default FALSE)

Side effect: Writes Hive-partitioned parquet tree to dest_dir.

cog_explain

Returns a named list with human-readable provenance for the most recent verb call.

Output fields: verb, target, years, category, codes_summed, aggregate_fallback, series_break_refs, manifest_sha, sql_query.

6. Provenance contract

Every verb result carries a provenance attribute (R list / JSON dict). All fields are required:

Field	Type	Description
verb	string	name of the verb
call	string	deparsed call expression
target	string[]	canonical_govids queried
years	int[]	years queried
category	string[] or null	categories queried
scope	object	manifest scope block
codes_summed	string[]	item_codes included in sum
aggregate_fallback	bool	true if any aggregate row was used
transformations	string[]	e.g. ["real_2022", "per_capita"]
series_break_refs	string[]	SB codes touching this query
manifest	object	manifest built_at + pipeline_commit
sql_query	string	DuckDB SQL executed

7. Scope handling

Readers MUST:

1. Read manifest.scope.gov_types_included on cog_open.
2. Error with a clear message if the corpus scope does not cover the government types the caller requested.
3. Never silently omit types that the caller expected to be present.

8. Series break awareness

Readers SHOULD surface warnings when a query spans a known series break. The canonical break list is in docs/series_breaks.md (also in the corpus docs/ directory). At minimum, warn on:

• Queries spanning FY2005 for categories with joinability != "yes".
• Queries spanning FY2017 (GID→PID transition) without canonical_govid reconciliation.

9. Versioning

manifest.schema_version	Reader Spec version	Notes
2	v0.1-draft	Never shipped: year=2012 partition mixed legacy + modern sources, producing duplicate (canonical_govid, item_code) rows. Do not consume.
3	v0.1	First shipped version. year=2012 is modern-source only; PID-era canonical_govid FIPS-bridged via canonical_fips_xwalk.
4	v0.1	Phase P canonical namespace: canonical_govid is now a uniform 12-char id (PID census_id frozen at FY2023 vintage, or a corpus-assigned 9xxxxx-unit id) for every government across its full observed life, replacing the mixed 9-char/12-char scheme. New metadata file canonical_alias.parquet (the resolver's only lookup table) ships alongside canonical_fips_xwalk.parquet. See docs/ids_reference.md § "Canonical namespace (Phase P)".
5	v0.1	Phase R2 harmonization: long schema grows 24→26 columns, adding harmonized_code (cross-vintage concept id) and survey_weight. New reference views *_harmonized, harmonization_map, harmonization_recipes, series_breaks_pq register when schema_version >= 5.
6	v0.1	Current. Long schema 26→28 columns. Breaking: fips_state_code→fips_state_asof, fips_county_code→fips_county_asof (rename, fails loudly); and fips_state/fips_county change MEANING to present/harmonized geography (silent — see the schema-v6 banner in §3). Build window extended to FY1967/1970; published floor lowered to FY1967 (dissolved-geography as-of-county NA-filled via data/dissolved_geographies.csv).

Breaking changes to the schema (column addition, type change, removed column) or to the partition semantics (source mixing, row count by unit-of-analysis) increment schema_version. Non-breaking changes (new parquet partition, doc update) do not.