> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dqlabs.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

> What a Lookup metric is in Prizm — validates column values against a reference source for referential integrity and controlled vocabulary checks.

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## What is a Lookup metric?

Lookup metrics validate **column values against a reference source** — checking that every value in a target column corresponds to a valid entry in an authoritative reference. They are the primary tool for referential integrity checks outside of database constraints, and for validating against controlled vocabularies, master data tables, REST APIs, reference files, and dynamically-queried reference sets.

**Type:** User-defined — Lookup metrics are created manually. Navigate to **Metric → Add** and select **Subcategory: Lookup**.

Lookup metrics answer the question: *Do the values in this column exist in the reference set they should come from?*

Prizm compares the target column values against the configured reference source on each run, computes a **match rate**, and trends it over time. Alerts fire when the match rate drops below the configured threshold or when new unseen values appear in the target column.

### Metrics

| Metric | Category       | Sub Category | Asset Level       | Description                                                                                                                                                                                                                      |
| ------ | -------------- | ------------ | ----------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Lookup | Reconciliation | Lookup       | Attribute / Asset | Validates one or more target columns against an external or internal reference source. Computes a match rate and flags unmatched, missing, or drifted values. Supports four source types: Table, API, Reference File, and Query. |

<CardGroup cols={2}>
  <Card title="Setup" icon="sliders" href="/architecture/metrics/lookup/setup">
    Step-by-step guide to creating and configuring a lookup metric.
  </Card>

  <Card title="Use Cases" icon="lightbulb" href="/architecture/metrics/lookup/usecases">
    Real-world examples — product catalog integrity, ISO code validation, cross-source customer ID checks.
  </Card>
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