chore: update readme and changelog

Author: Yuri Zmytrakov

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Added
 
+- Added CQL2 Abstract Syntax Tree (AST) structure for efficient query parsing and datetime-based indexes. [#560](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/560)
+
 - Environment variable `VALIDATE_QUERYABLES` to enable/disable validation of queryables in search/filter requests. When set to `true`, search requests will be validated against the defined queryables, returning an error for any unsupported fields. Defaults to `false` for backward compatibility.[#532](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/532)
 
 - Environment variable `QUERYABLES_CACHE_TTL` to configure the TTL (in seconds) for caching queryables. Default is `1800` seconds (30 minutes) to balance performance and freshness of queryables data. [#532](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/532)

README.md

@@ -100,6 +100,7 @@ This project is built on the following technologies: STAC, stac-fastapi, FastAPI
   - [Examples](#examples)
   - [Performance](#performance)
     - [Direct Response Mode](#direct-response-mode)
+    - [CQL2 JSON Search with AST-based Parsing](#cql2-json-search-with-ast-based-parsing)
   - [Quick Start](#quick-start)
     - [Installation](#installation)
     - [Running Locally](#running-locally)
@@ -379,6 +380,31 @@ These examples provide practical reference implementations for various deploymen
 - **Default setting**: `false` for safety.
 - **More information**: See [issue #347](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/issues/347) for background and implementation details.
 
+
+### CQL2 JSON Search with AST-based Parsing
+
+SFEOS now uses an Abstract Syntax Tree (AST) in CQL2-JSON search queries for efficient query parsing and datetime extraction, enabling the selection and management of the appropriate searchable indexes.
+
+#### AST-based Query Processing
+
+The CQL2 implementation uses an Abstract Syntax Tree (AST) structure that replaces the previous dictionary-based processing. This enables:
+
+1. **Structured Query Representation**: Queries are parsed into a tree structure with different node types
+2. **Efficient Parameter Access**: Easy traversal and extraction of query parameters
+3. **Optimized Index Selection**: Selection of appropriate fields for selection and management of indexes
+
+#### AST Node Types
+
+The AST supports various node types representing different query operations:
+
+- **Logical Nodes**: `AND`, `OR`, `NOT` operators for combining conditions
+- **Comparison Nodes**: `=`, `<>`, `<`, `<=`, `>`, `>=`, `isNull` operations
+- **Advanced Comparison Nodes**: `LIKE`, `BETWEEN`, `IN` operations
+- **Spatial Nodes**: `s_intersects`, `s_contains`, `s_within`, `s_disjoint` for geospatial queries
+- **Datetime Nodes**: Special handling for datetime range and exact value queries
+
+The AST-based approach enables efficient extraction of datetime parameters (`datetime`, `start_datetime`, `end_datetime`) from complex queries.
+
 ## Quick Start
 
 This section helps you get up and running with stac-fastapi-elasticsearch-opensearch quickly.