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priyanshijanipriyanshijani/data-agents/skills/data-quality/SKILL.md

data-quality

Skill0 starsChanged 43 days agoMITView on GitHub

Vera's data quality playbook. Covers profiling, rule design across seven quality dimensions, BLOCK/WARN/INFO severity, a metadata-driven PySpark rules engine with quarantine, equivalents for Great Expectations, Soda, dbt tests, Lakeflow/DLT expectations and Deequ, layer-by-layer reconciliation for root-cause analysis, and freshness/volume/schema monitoring. Use when designing DQ checks, validating data, or investigating wrong numbers.

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SKILL.md

Data Quality Playbook

NeedOpen
Profile a table before designing rulesreferences/profiling.md
Metadata-driven PySpark rules engine + quarantinereferences/rules-engine-pyspark.md
Same rules in Great Expectations / Soda / dbt / DLT / Deequreferences/engines.md
"The numbers are wrong", root-cause and reconciliationreferences/investigation.md
Freshness, volume, schema and drift monitoringreferences/monitoring.md

Seven dimensions (plus schema)

DimensionQuestionTypical checks
CompletenessIs anything missing?not-null on keys, null % ≤ threshold, expected partitions present
UniquenessIs anything duplicated?unique business key, no duplicate loads
ValidityAre values allowed?ranges, enums/accepted values, regex formats, date sanity (not in the future, not before 1990)
ConsistencyDo related values agree?cross-column rules (end ≥ start, total = qty × price ± tolerance), same key means the same attributes across sources
TimelinessIs it fresh?now − max(event_ts) ≤ SLA, watermark lag
VolumeIs the amount plausible?row count within a band vs trailing history, per tenant
Referential integrityDo references resolve?FK exists in dimension (orphan rate ≤ threshold)
SchemaIs the shape as agreed?expected columns and types, no unexpected new columns (contract)

Severity

LevelMeaningAction
BLOCKPublishing would corrupt downstream data or decisionsFail the run, don't publish, alert
WARNSuspicious but usablePublish, log, alert the owner; quarantine failing rows if row-level
INFOObservability metricLog only; used for trends and tuning thresholds

A rule starts as WARN while it's new. It becomes BLOCK after two weeks without false positives. This keeps a new rule from stopping production on its first night.

Choosing an engine (when data_quality.engine is blank)

StackRecommend
Databricks + Lakeflow Declarative PipelinesDLT expectations (expect, expect_or_drop, expect_or_fail) + native results table
Databricks notebooks / any SparkNative PySpark rules engine (this playbook), or Great Expectations for rich docs
dbt anywheredbt tests + model contracts (+ dbt-expectations package)
Mixed warehouses, analyst-authored rulesSoda (SodaCL YAML)
Very large Spark on AWS/EMRDeequ / PyDeequ

Threshold rules of thumb

  • Derive from the profile: threshold = observed p99 (or max) + margin. Record the baseline and date in the rule description.
  • Volume bands: use a day-of-week-aware trailing 4–8 week median ± k·MAD. It's more robust than mean ± σ.
  • Say which rules are business decisions, such as whether negatives are allowed, which statuses are valid, or what SLA the business needs. Those need a human to confirm.

Output contract for every check

rule_id, table_name, dimension, severity, passed, actual_value, threshold, failed_rows, sample_keys, run_id, checked_at

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