Merge branch 'master' into remove-zetasql

Author: peytondmurray

g3doc/custom_data_validation.md

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+# Custom Data Validation
+
+<!--*
+freshness: { owner: 'kuochuntsai' reviewed: '2022-11-29' }
+*-->
+
+TFDV supports custom data validation using SQL. You can run custom data
+validation using
+[validate_statistics](https://github.com/tensorflow/data-validation/blob/master/tensorflow_data_validation/api/validation_api.py;l=236;rcl=488721853)
+or
+[custom_validate_statistics](https://github.com/tensorflow/data-validation/blob/master/tensorflow_data_validation/api/validation_api.py;l=535;rcl=488721853).
+Use `validate_statistics` to run standard, schema-based data validation along
+with custom validation. Use `custom_validate_statistics` to run only custom
+validation.
+
+## Configuring Custom Data Validation
+
+Use the
+[CustomValidationConfig](https://github.com/tensorflow/data-validation/blob/master/tensorflow_data_validation/anomalies/proto/custom_validation_config.proto)
+to define custom validations to run. For each validation, provide an
+SQL expression, which returns a boolean value. Each SQL expression is run
+against the summary statistics for the specified feature. If the expression
+returns false, TFDV generates a custom anomaly using the provided severity and
+anomaly description.
+
+You may configure custom validations that run against individual features or
+feature pairs. For each feature, specify both the dataset (i.e., slice) and the
+feature path to use, though you may leave the dataset name blank if you want to
+validate the default slice (i.e., all examples). For single feature validations,
+the feature statistics are bound to `feature`. For feature pair validations, the
+test feature statistics are bound to `feature_test` and the base feature
+statistics are bound to `feature_base`. See the section below for example
+queries.
+
+If a custom validation triggers an anomaly, TFDV will return an Anomalies proto
+with the reason(s) for the anomaly. Each reason will have a short description,
+which is user configured, and a description with the query that caused the
+anomaly, the dataset names on which the query was run, and the base feature path
+(if running a feature-pair validation). See the section below for example
+results of custom validation.
+
+See the
+[documentation](https://github.com/tensorflow/data-validation/blob/master/tensorflow_data_validation/anomalies/proto/custom_validation_config.proto)
+in the `CustomValidationConfig` proto for example
+configurations.