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Module:

CQL Parser

Module Maintainer:

Mauricio Pazos

Email Help:

Geotools-gt2-users@lists.sourceforge.net

Volunteer:

geotools-devel@lists.sourceforge.net

Status:

(star) (star) (star) (star) (star)

Model 

CQL Parser Design; ECQL Parser Design

User doc

14 CQL

Gold Star Quality Assurance Check:

(star) IP Check: need to ensure all headers are in place
(star) Releasable: no blocking issues
(star) Quality Assurance: 84.9% test coverage reported by clover
(star) Stability: based on reviewed GeoAPI Filter interfaces and reviewed CSW 2.0.1 BNF for CQL
(star) user and design docs. Module maintainer does watches user list, answers email.

Target

A module dedicated to fully support the OGC Common Query Language, version 2.0.1, as a query predicate language inside GeoTools.

Motivation

Axios has developed, for the Gipuzkoa Provincial Council, Mobility and Land Planning Department, an implementation of the OGC Catalog Service for Web 2.0.1 specification, based on GeoAPI medatada interfaces and Geotools implementation to support the ISO-19115/19139 profile.

The CSW specification, in section 6.2.2 defines the complete BNF for a constraint language to use as query predicates in a CSW implementation, named OGC Common Query Language, CQL for short.

As the CSW implementation worked on useing exclusively org.opengis.filter.Filter, it was needed a converter from an input query, in CQL format, to an equivalent predicate in the form of a Filter object.

Target Audience

By being part of the GeoTools library, this little module would just allow for any client code to easily construct a filter using a more human friendly predicate language.

In particular, the GeoServer community is currently willing to use it to add friendly filtering capabilities in WMS GetMap requests, and I guess it could be used in WFS GetFeature too.

An example usage would be:

Ofcourse the quoted text after CONSTRAINT= should be properly encoded for HTTP

History

The module is derived from the old org.geotools.filter.ExpressionBuilder parser by Ian Schneider.

The focus was to fully support the 2.0.1 version of the BNF as defined in the CSW spec. This implies, among other improvements:

  • support for nested and prefixed property names (for example, gmd:MD_Metadata.identificationInfo.gmd:MD_DataIdentification.abstract)
  • support for spatial predicates (intersect, touches, etc). Note that the BNF oddly suppressed the trailing 's' from these predicates, so TOUCH(ATTR1, POINT(1 2)) instead of TOUCHES(ATTR1, POINT(1 2))
  • temporal predicates (BEFORE, AFTER, DURING, etc)

Design Overview

The diagram presents the cql module published interface. The showed classes, CQL and ECQL, implement the contract with the clients. You can find other public classes in packages such as common and generated, but they are intended as internal interface (part of the implementation). They are not part of CQL module contract, so you should not use those classes.

In the below figure are presented the main package relations. The generated package maintains all classes generated by javacc. The cql2 and ecql packages implement the parsing and filter construction for OGC CQL and ECQL languages, respectively. In the commons are encapsulated the utility classes required to implement the module behavior.

To know more about CQL module implementation, see the following links:

Status

The module is in good health. No self or transient issues preventing it from compiling and passing tests.

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