Update Changlog and Known Issues for V0.0.1 Release

Author: Jamestth

CHANGELOG.md

@@ -8,12 +8,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 - Nil
 
-## [0.0.1] - 2026-04-01
+## [0.0.1] - 2026-04-02
 
-Initial public release of **vowl** (formerly DQMK).
+### 🎉 Celebrating Open Source
 
-### Added
+Initial public release of **vowl**.
+
+**Background:**
 
+- vowl originated as an internal tool for demonstrating data contracts within our prototyping workflows. Over time, we recognised its potential value to the wider international community.
+- With that in mind, we refined the library and published it as open source.
+- As the project is still in its early stages, there may be rough edges and bugs. We appreciate your patience and warmly welcome contributions to help improve vowl for everyone.
+
+### Added
 - Core SQL-powered data quality validation engine backed by Ibis and DuckDB.
 - Contract-based validation with YAML/JSON schema definitions.
 - Adapters for pandas, Spark, and database backends (DuckDB attach).

docs/known-issues.md

@@ -63,6 +63,26 @@ The `MultiSourceSQLExecutor` materialises tables via Arrow instead of using Duck
 
 ---
 
+## Null Handling Varies Across Database Backends
+
+Different database backends handle `NULL` values differently in generic checks such as `minimum`, `maximum`, and `mean`. Some backends silently skip `NULL` rows when computing aggregates, while others may include them or produce unexpected results. This means a column containing `NULL` values might still pass a `minimum` or `maximum` check because the nulls are ignored during evaluation.
+
+If you need to guarantee that a column contains **no null values**, add an explicit `nullValues` library check rather than relying on aggregate checks to catch them:
+
+```yaml
+properties:
+  - name: my_column
+    quality:
+      - id: my_column_no_nulls
+        metric: nullValues
+        mustBe: 0
+        description: "There must be no null values in the column."
+```
+
+This ensures nulls are caught directly, regardless of which database backend is running the validation.
+
+---
+
 ## Dark Patterns
 
 ### Queries Accessing Tables Outside the Contract