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| 1 | +**Catalog Metadata Recommendations for LLM Semantic Layer** |
| 2 | + |
| 3 | +Purpose |
| 4 | +- Provide recommended metadata items and annotations to add to datasets, columns, and related catalog entities so LLMs can accurately discover, interpret, and ground answers using the catalog data. |
| 5 | + |
| 6 | +How to read this document |
| 7 | +- For each metadata item: **What** the item is, **How to create/store/maintain** it, and **How an LLM will use it**. |
| 8 | + |
| 9 | +1) Dataset-level metadata |
| 10 | +- Description |
| 11 | + - What: Concise human-readable overview of dataset purpose, scope, and typical use-cases (2–4 sentences). Link to detailed README when available. |
| 12 | + - Create/Store/Maintain: Store as a catalog field (`description`). Keep in repo or metastore README and surface in the catalog UI. Update via CI when schema or owners change; include last-updated timestamp and version. |
| 13 | + - LLM usage: Provides context for retrieval and prompt grounding; used to choose relevant datasets and to craft natural-language explanations. |
| 14 | + |
| 15 | +- Owner & contacts |
| 16 | + - What: Dataset owner, steward, and on-call contacts; GitHub/Slack/email links. |
| 17 | + - Create/Store/Maintain: Store as structured fields (`owner`, `steward`, `contact`). Sync with org directory or Git metadata; validate via periodic checks. |
| 18 | + - LLM usage: When answers require clarification or approval, LLMs can surface contacts and generate recommended outreach text. |
| 19 | + |
| 20 | +- Sensitivity / Classification / PII tag |
| 21 | + - What: One or more classification labels (e.g., `public`, `internal`, `confidential`, `restricted`, `pii`), plus GDPR/CCPA flags. |
| 22 | + - Create/Store/Maintain: Use controlled vocabulary; store as structured tags. Apply automated PII detectors and manual review. Enforce policy on ingest and propagation to column-level. |
| 23 | + - LLM usage: Filter retrieval and enforce redaction/response constraints; avoid exposing sensitive values; add safety warnings to generated content. |
| 24 | + |
| 25 | +- Freshness & cadence |
| 26 | + - What: `last_updated`, `update_frequency` (daily/hourly/real-time), `data_latency` (how stale data typically is). |
| 27 | + - Create/Store/Maintain: Populate from ingestion pipelines; update automatically in ETL. Include source commit/manifest versions for reproducibility. |
| 28 | + - LLM usage: Prefer fresher sources for time-sensitive answers; indicate confidence based on age of data. |
| 29 | + |
| 30 | +- Row count & high-level statistics |
| 31 | + - What: Approximate `row_count`, record size, table size, partition layout summary. |
| 32 | + - Create/Store/Maintain: Compute during ingestion or via scheduled jobs; update metrics store. |
| 33 | + - LLM usage: Assess reliability and representativeness; help prioritize datasets for retrieval. |
| 34 | + |
| 35 | +- Business domain & canonical terms |
| 36 | + - What: Business domain name (e.g., `billing`, `customer-360`) and canonical dataset tags mapped to an ontology or glossary. |
| 37 | + - Create/Store/Maintain: Maintain a central business glossary; link dataset to canonical terms via IDs. |
| 38 | + - LLM usage: Map user queries to domain-specific datasets; disambiguation and slot-filling during query-generation. |
| 39 | + |
| 40 | +- Lineage & provenance |
| 41 | + - What: Source systems, upstream datasets, transformations, jobs, timestamps, and commit hashes. |
| 42 | + - Create/Store/Maintain: Capture automatically in ETL frameworks (e.g., as part of job metadata). Store as structured lineage graph or DAG references. |
| 43 | + - LLM usage: Provide provenance evidence, justify answers, enable traceability and chain-of-thought grounding. |
| 44 | + |
| 45 | +- Sample rows / schema examples |
| 46 | + - What: Small anonymized sample (10–50 rows) or schema-typed examples demonstrating typical values. |
| 47 | + - Create/Store/Maintain: Generate from dataset with redaction for PII; store as reversible or irreversible sampled snapshot depending on policy. |
| 48 | + - LLM usage: Help the model understand value formats and craft better queries and extraction prompts. |
| 49 | + |
| 50 | +2) Column-level metadata |
| 51 | +- Column description |
| 52 | + - What: Natural-language description of what the column represents and business interpretation. |
| 53 | + - Create/Store/Maintain: Add as `description` on column definitions; source from data producers and data stewards. Keep small and precise. |
| 54 | + - LLM usage: Crucial for mapping natural-language attributes to schema fields when generating queries or answering questions. |
| 55 | + |
| 56 | +- Semantic type / ontology mapping |
| 57 | + - What: Semantic tag (e.g., `email`, `currency`, `timestamp`, `country`, `user_id`) and link to canonical ontology term. |
| 58 | + - Create/Store/Maintain: Standardize tags (controlled vocabulary) and map via schema/registry. Use detectors to suggest mappings; require steward approval. |
| 59 | + - LLM usage: Improves normalization, unit-aware reasoning, and safe handling (PII awareness). Helps in entity linking and canonicalization. |
| 60 | + |
| 61 | +- Units & format |
| 62 | + - What: Units (`USD`, `meters`), timezone for timestamps, expected format (ISO date, RFC3339), regex examples. |
| 63 | + - Create/Store/Maintain: Maintain as metadata fields; validate in ETL and during schema checks. |
| 64 | + - LLM usage: Enables correct conversions, comparisons, and localized formatting in answers. |
| 65 | + |
| 66 | +- Value examples / top values |
| 67 | + - What: 5–10 typical or top cardinal values, plus common error patterns. |
| 68 | + - Create/Store/Maintain: Compute periodically; keep derived stats (top-k values, distinct_count, null_fraction). |
| 69 | + - LLM usage: Supports disambiguation, common-case assumptions, and helps avoid hallucinating unexpected values. |
| 70 | + |
| 71 | +- Cardinality & distinct count |
| 72 | + - What: High-cardinality flag, distinct counts, null ratio, and uniqueness (candidate primary key). |
| 73 | + - Create/Store/Maintain: Compute in metrics jobs; update with data refresh. |
| 74 | + - LLM usage: Guide join strategy, entity resolution, and explainability of joins. |
| 75 | + |
| 76 | +- Referential links (foreign keys) |
| 77 | + - What: Declared relationships to other dataset columns (FK -> primary key reference). |
| 78 | + - Create/Store/Maintain: Detect via profiling or declare in schema; validate periodically. |
| 79 | + - LLM usage: Assist query planning, join recommendations, and preserving referential integrity when constructing SQL. |
| 80 | + |
| 81 | +- Derived / computed flag & transform expression |
| 82 | + - What: Whether column is derived; store the transformation SQL/logic or pointer to transformation job. |
| 83 | + - Create/Store/Maintain: Capture in ETL metadata and code repository; version the expression. |
| 84 | + - LLM usage: Explain derivation and enable tracing of how reported values were produced. |
| 85 | + |
| 86 | +3) File/manifest/partition-level metadata |
| 87 | +- Storage format & location |
| 88 | + - What: File type (Parquet/CSV/ORC), bucket/path, partitioning scheme and partition keys. |
| 89 | + - Create/Store/Maintain: Store in manifest metadata and file manifest; keep hashes and sizes per file. |
| 90 | + - LLM usage: Answer storage/availability questions; determine efficient access patterns and cost estimates. |
| 91 | + |
| 92 | +- Partition statistics |
| 93 | + - What: Per-partition row counts, min/max values for partition keys, and freshness per partition. |
| 94 | + - Create/Store/Maintain: Aggregated by ingestion jobs; indexed by partition. |
| 95 | + - LLM usage: Helps narrow retrieval to relevant partitions for RAG pipelines and to limit data scanned. |
| 96 | + |
| 97 | +4) Catalog-level artifacts useful to LLMs |
| 98 | +- Business glossary & term definitions |
| 99 | + - What: Canonical business definitions, synonyms, and mappings to schema elements. |
| 100 | + - Create/Store/Maintain: Central glossary service or JSON-LD store; tie terms to dataset/column IDs. |
| 101 | + - LLM usage: Disambiguate user language to schema; provide more accurate slot filling and entity resolution. |
| 102 | + |
| 103 | +- Embeddings & vector indexes |
| 104 | + - What: Semantic embeddings for dataset descriptions, column descriptions, sample rows, and business terms. |
| 105 | + - Create/Store/Maintain: Generate with a chosen encoder; store vectors in a vector DB with pointers to canonical IDs and timestamps. Recompute on description or sample updates. |
| 106 | + - LLM usage: Retrieval-augmented generation (RAG): find the most relevant schema pieces, example rows, and docs for prompts. |
| 107 | + |
| 108 | +- Index of FAQ / usage examples / canned queries |
| 109 | + - What: Curated list of example queries, typical SQL snippets, common pitfalls, and recommended joins. |
| 110 | + - Create/Store/Maintain: Curated by data stewards; surfaced via dataset README and catalog UI. |
| 111 | + - LLM usage: Use examples as few-shot context to improve generated queries and recommended actions. |
| 112 | + |
| 113 | +- Data quality rules & test results |
| 114 | + - What: Rules (uniqueness, ranges, not-null) and latest validation outcomes with severity. |
| 115 | + - Create/Store/Maintain: Store test definitions and results in metadata store; CI gating for failing tests. |
| 116 | + - LLM usage: Modify confidence, add caveats to answers, and suggest remediation steps. |
| 117 | + |
| 118 | +5) Formats and storage recommendations |
| 119 | +- Use structured, machine-readable metadata (JSON / JSON-LD) |
| 120 | + - Why: LLMs and downstream services can easily parse and ingest structured fields; JSON-LD helps link to ontologies. |
| 121 | + |
| 122 | +- Use a single source-of-truth metastore |
| 123 | + - Why: Consistency for ingestion, tooling and LLM retrieval. Options: existing metastore (Hive/Glue/BigQuery/Firestore), Data Catalog solutions (OpenMetadata, Apache Atlas), or a small dedicated metadata DB linked to the catalog. |
| 124 | + |
| 125 | +- Versioning and immutability |
| 126 | + - Why: Keep historical context available for provenance and reproducibility. Store `schema_version`, `metadata_version`, and stable dataset identifiers. |
| 127 | + |
| 128 | +- Vector store for embeddings |
| 129 | + - Why: Fast semantic retrieval. Keep vector metadata pointing back to canonical IDs; store embedding model name and timestamp. |
| 130 | + |
| 131 | +- Controlled vocabularies and schemas |
| 132 | + - Why: Predictable semantics for LLM prompts. Define enumerations for classification, semantic types, sensitivity, update frequency. |
| 133 | + |
| 134 | +6) Ingestion & maintenance guidance |
| 135 | +- Automated extraction |
| 136 | + - Create jobs that generate or update: descriptions (seeded then curated), statistics, sample rows (PII redacted), tests, lineage. |
| 137 | + |
| 138 | +- Review workflow |
| 139 | + - Provide suggested changes automatically (profiling/detectors), but require steward human approval for semantic fields (descriptions, sensitivity, canonical mapping). |
| 140 | + |
| 141 | +- Frequency & triggers |
| 142 | + - Update statistics and embeddings on refresh cycles or schema change; update descriptions and lineage when ETL code or owner changes. |
| 143 | + |
| 144 | +- Audit & access control |
| 145 | + - Maintain audit logs of metadata changes and who changed them. Enforce RBAC for who can change sensitivity or owner. |
| 146 | + |
| 147 | +7) How LLMs will consume and use these items |
| 148 | +- Retrieval & grounding |
| 149 | + - LLMs will use dataset and column descriptions, embeddings, and sample rows to select relevant data and ground responses in factual sources. |
| 150 | + |
| 151 | +- Query generation (SQL/filters) |
| 152 | + - Column semantics, units, and sample values let the LLM map natural-language predicates into typed SQL fragments, reducing malformed queries. |
| 153 | + |
| 154 | +- Safety & policy enforcement |
| 155 | + - Use sensitivity tags and PII flags to block or redact results and to insert safety disclaimers in generated output. |
| 156 | + |
| 157 | +- Explainability & provenance |
| 158 | + - Lineage and transform expressions allow the LLM to explain how values were derived and link back to data sources. |
| 159 | + |
| 160 | +- Confidence estimation |
| 161 | + - Use freshness, data quality results, and row counts to set answer confidence and create caveats for the user. |
| 162 | + |
| 163 | +- Disambiguation & entity linking |
| 164 | + - Use business glossary + ontology mappings so the LLM can resolve ambiguous user terms to canonical schema elements. |
| 165 | + |
| 166 | +8) Implementation checklist & examples |
| 167 | +- Minimum viable metadata to onboard a dataset |
| 168 | + - `description`, `owner`, `sensitivity`, `last_updated`, column `description`, column `semantic_type`, and `schema`. |
| 169 | + |
| 170 | +- Recommended full set (for production LLM usage) |
| 171 | + - All dataset-level items in section 1, all column-level in section 2, embeddings, glossary links, lineage, DQ rules, and sample rows. |
| 172 | + |
| 173 | +- Example JSON snippet (dataset metadata) |
| 174 | + - { |
| 175 | + "dataset_id": "billing.transactions.v1", |
| 176 | + "description": "Transaction-level events for billing.", |
| 177 | + "owner": "team-billing@example.com", |
| 178 | + "sensitivity": "internal", |
| 179 | + "last_updated": "2026-01-10T12:00:00Z", |
| 180 | + "row_count": 12345678, |
| 181 | + "tags": ["billing","payments"], |
| 182 | + "glossary_terms": ["invoice","chargeback"] |
| 183 | + } |
| 184 | + |
| 185 | +9) Security, privacy, and governance notes |
| 186 | +- Redaction and synthetic samples |
| 187 | + - Never store raw PII in sample rows unless explicitly approved; use redaction or synthetic replacements. |
| 188 | + |
| 189 | +- Embedding privacy |
| 190 | + - Beware of embedding models that can memorize; strip raw PII before embedding and record embedding provenance. |
| 191 | + |
| 192 | +- Policy enforcement |
| 193 | + - Enforce access control at retrieval time using sensitivity tags; LLM layer must check authorization before exposing content. |
| 194 | + |
| 195 | +10) Next steps & suggested rollout |
| 196 | +- Phase 1 (MVP): Add `description`, `owner`, `sensitivity`, `last_updated`, column `description`, column `semantic_type`, and compute basic stats and sample rows (redacted). |
| 197 | +- Phase 2: Add lineage capture, DQ rules, vector embeddings for descriptions and samples, and top-value statistics. |
| 198 | +- Phase 3: Full integration with glossary/ontology, automated detectors, and UI surfaces for steward approval. |
| 199 | + |
| 200 | +Contact / Review |
| 201 | +- Please review and indicate priority items to implement first. For implementation I can scaffold extractor jobs, a JSON schema for metadata, or a small metastore adapter for this repository. |
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