.. _filter_syntax:

Supported filter languages
====================================

Data filtering in GeoServer is based on the concepts found in the `OGC Filter Encoding Specification <http://www.opengeospatial.org/standards/filter>`_.

GeoServer accepts filters encoded in two different languages: *Filter Encoding* and *Common Query Language*.  

Filter Encoding
---------------

The **Filter Encoding** language is an XML-based method for defining filters.
XML Filters can be used in the following places in GeoServer:

- in WMS ``GetMap`` requests, using the ``filter`` parameter
- in WFS ``GetFeature`` requests, using the ``filter`` parameter
- in SLD Rules, in the :ref:`Filter <sld_intro>` element

The Filter Encoding language is defined by `OGC Filter Encoding Standards <http://www.opengeospatial.org/standards/filter>`_:

- Filter Encoding 1.0 is used in WFS 1.0 and SLD 1.0
- Filter Encoding 1.1 is used in WFS 1.1
- Filter Encoding 2.0 is used in WFS 2.0

CQL/ECQL
--------

**CQL (Common Query Language)** is a plain-text language created for the *OGC Catalog* specification.
GeoServer has adapted it to be an easy-to-use filtering mechanism.
GeoServer actually implements a more powerful extension called **ECQL (Extended CQL)**,
which allows expressing the full range of filters that *OGC Filter 1.1* can encode. 
ECQL is accepted in many places in GeoServer:

- in WMS ``GetMap`` requests, using the :ref:`cql_filter <wms_vendor_parameters>` parameter 
- in WFS ``GetFeature`` requests, using the :ref:`cql_filter <wfs_vendor_parameters>` parameter
- in SLD :ref:`dynamic symbolizers <pointsymbols>`

The :ref:`filter_ecql_reference` describes the features of the ECQL language.
The  :ref:`cql_tutorial` tutorial shows examples of defining filters.

The CQL and ECQL languages are defined in:

- `OpenGIS Catalog Services Specification <http://portal.opengeospatial.org/files/?artifact_id=3843>`_ contains the standard definition of CQL 
- `ECQL Grammar <https://github.com/geotools/geotools/blob/master/modules/library/cql/ECQL.md>`_ is the grammar defining the GeoTools ECQL implementation