OSGeodata metadata exchange protocol: Unterschied zwischen den Versionen

Aktuelle Version vom 31. Januar 2009, 21:10 Uhr

We need a geographic metadata exchange protocol! And let's reduce it to the max.

This is part of a discussion around a geographic metadata exchange model and a geographic metadata exchange protocol. See also OSGeodata Discovery and generally OSGeodata.

Overview

A protocol specification consists of requests (operations) and responses (information model encoded in a streaming format and error messages, as codes).

We distinguish specifically query/search protocols and harvesting procotols. Metadata harvesting refers to the sharing of metadata records through protocols, APIs, and services which are designed specifically to facilitate this task. From the point of view of a data provider it's rather syndication or dissemination, from the point of view of a service provider it's collecting or aggregating ('gathering' in search engine technology).

The final goal is to define and implement "a protocol for the incremental exchange of metadata about geographic resources between systems".

After having agreed on a better protocol there is also a need for a better name than 'Geographic Catalog Service or Protocol', like 'Geographic Metadata Harvesting Protocol'.

Distributed Searching or Harvesting (with central index)?

See OSGeodata_Discovery for a discussion.

We propose the following specifications for a Geographic Metadata Harvesting Protocol:

1. Use HTTP and XML ('autonomous discovery'/'autonomous data provider')
2. OAI-PMH including a comparison with WFS (profiled) ('dependent data provider')

CSW, WFS and for example SRU/SRW are implementations of a search protocol. Proposals like OGC's CSW 2.0 do not fulfill these requirements. Profiled specifications like OAI-PMH or WFS are currently on our short list (see Proposals below).

Proposals

We need a protocol for the discovery of geodata which is open, lean and mean.

Thus we tend to propose a harvesting approach which means, that

1. in a first step data according to OSGeodataMetadataModel and encoded as XML files are published
2. and in a second step OAI-PMH could be utilized, moving around the same XML files.

Better name sought (catalogue is probably not the most appropriate noun):

• Geographic Metadata Syndication Protocol (my favourite)
• Geographic Metadata Harvesting Protocol
• Other proposals?
  • Geographic Data Discovery Protocol
  • Geographic Metadata Dissemination Protocol

Weblinks

• Simple Catalog Interface at OSGeo Wiki as well as the OSGeodata mailing list mentioned above
• OAI-PMH - including home, wikipedia, documents, tutorials, tools and demos
• Introduction to the IESR: A Registry of Collections and Services, by Hill and Ann Apps, MIMAS, Univ. of Manchester, 2006.
• Other
  • OGC's CSW 2.0
  • OGC's WFS
• Miscellaneous
  • THUMP - The HTTP URL Mapping Protocol, IETF Draft, June 2006.