📖 技能介绍

name: data-model description: Deep data modeling workflow—grain, facts and dimensions, keys, slowly changing dimensions, normalization trade-offs, and analytics query patterns. Use when designing warehouse/analytics models or reviewing star/snowflake schemas.

Data Model

Analytics models succeed when grain is explicit, keys are stable, and slowly changing dimensions are chosen deliberately—not “star schema by default.”

When to Offer This Workflow

Trigger conditions:

Designing a warehouse, lakehouse, or BI layer
Confusion on one row per what; duplicate counts in reports
Refactoring dimensional models for performance or clarity

Initial offer:

Use six stages: (1) business questions & grain, (2) conformed dimensions, (3) facts & measures, (4) dimensions & SCD types, (5) keys & integrity, (6) performance & evolution). Confirm tooling (dbt, dimensional DW, BigQuery, etc.).

Stage 1: Business Questions & Grain

Goal: Grain = the atomic row: e.g., “one line item per order per day” not “sort of per order.”

Practices

List questions the model must answer; derive grain from smallest needed detail

Exit condition: One sentence grain per fact table.

Stage 2: Conformed Dimensions

Goal: Same customer/product definitions across facts—shared dimension tables or SCD policy aligned.

Stage 3: Facts & Measures

Goal: Additive vs semi-additive vs non-additive measures documented (balances, distinct counts).

Practices

Degenerate dimensions vs junk dimensions—avoid wide fact sprawl without reason

Stage 4: Dimensions & SCD Types

Goal: SCD1 overwrite vs SCD2 history with valid_from/valid_to vs SCD3 limited history—match compliance and reporting needs.

Stage 5: Keys & Integrity

Goal: Surrogate keys in facts; natural keys preserved as attributes; referential integrity strategy in the warehouse layer.

Stage 6: Performance & Evolution

Goal: Partition and cluster keys for large facts; late-arriving facts policy; version dims when schema evolves.

Final Review Checklist

[ ] Grain explicit per fact table
[ ] Conformed dimensions planned
[ ] Measure additivity documented
[ ] SCD strategy per critical dimension
[ ] Keys and late-arriving data handled

Tips for Effective Guidance

Fan traps and chasm traps in BI—flag when joining across facts incorrectly.
Snapshot fact tables for point-in-time balances vs transaction facts.