RFC 4: CSW 3.0 support

date: 2015-06-28
author: Tom Kralidis, Angelos Tzotsos
contact: tomkralidis@gmail.com, tzotsos@gmail.com
status: draft
modified: 2015-07-02

Overview

This RFC describes the pycsw implementation of the OGC Catalogue Services 3.0 Specification - HTTP Protocol Binding (OGC 12-176r5).

CSW 3.0 provides major features and improvements over CSW 2.0.2 as part of the evolution of OGC Catalogue Services, including Open Search Geo and Time Extensions, OpenSearch 1.1, and the Atom Syndication Format. Other enhancements include:

features advertised as conformance classes
simpler KVP API
enhanced distributed searching functionality
raw metadata response for GetRecordById
proper use of HTTP status codes
proper use of HTTP request/response headers
UnHarvest operation
use of temporal predicates for query and presentation

Catalogue Services 3.0 - General Model (OGC 12-168r5) encompasses numerous changes (hence the major version change) to Catalogue Services overall. This RFC (and pycsw) focuses exclusively on the HTTP Protocol Binding.

Proposed Solution

Given the major changes in CSW 3.0, pycsw requires significant refactoring to support multiple verisons of numerous specifications (CSW, Filter Encoding, OWS Common, GML, etc.). A high level design pattern includes:

specifications implemented outside of the core server
generic dispatcher (pycsw.server.Csw)
version detection / negotiation determines code path

Implementation

Activating the feature

CSW 3.0 support will be enabled by default. The default version will be CSW 3.0 in accordance with the specification. For backwards compatibility, there may implement a configuration directive which forces CSW 2.0.2 first.

Files affected

codebase: this RFC affects the entire codebase
tests: a csw3 test suite will be added
docs: the documentation will be augmented to advertise support and describe changes and default version behaviour

Backwards Compatibility Issues

This RFC represents breaking backwards compatibility in terms of default version. For downstream applications, pycsw.server.Csw will continue to exist, and will accept a version argument to force CSW 2.0.2 behaviour if desired. Unit tests will continue to succeed with a new csw30 test suite added. In addition, CITE tests will be 100% successful.

Internal Interface changes

pycsw.server.Csw will continue to exist, and will accept a version argument to force CSW 2.0.2 behaviour if desired.

Performance Implications

None expected.

None

Restrictions

None

Documentation

Documentation will be augmented to advertise support and describe changes and default version behaviour.

Miscellaneous

Status

Adopted on 2015-07-02