Geodata Discovery: Unterschied zwischen den Versionen

Version vom 20. April 2010, 10:47 Uhr

Geodata Discovery Specification - Discovery of Geodata and Geospatial Services

Status

• Version 1.00, 19.4.2010, Stefan Keller -- First release of the specification.

Introduction

Overview

The discovery of geodata and geospatial services is crucial of almost every project which involves geoprocessing and therefore also to every (geo) data infrastructure!

General purpose search engines are not capable of recognizing geodata formats and geospatial services. Thus, here is a strong need to support geospatial search services, especially repositories and webcrawlers. The solution is twofold: first help machines find explicitely resources they are looking for (through relation links) and, second, let users realize and control that they are browsing a web site which is enhanced with those machine readable relationships (through an icon).

Instead of a web of (HTML) documents, this is part of a vision about a web of services (and XML) which what (semantic) Web 2.0 is mostly about. "So it is vital at the GeoWeb align itself with the web and the multitude of sources and endpoints that the web is reaching into." (citation form High Earth Orbit blog).

Relationship to other standards

This specification doesn't require any change to any of the formats and standards mentioned. In fact, it's just a recommendation for a common usage of these formats.

robots.txt and sitemaps.xml from Google are somehow similar because the refer to contents. The harvesting protocol OAI-PMH includes also a "See also" element. Beyond this there is no similar standard for discovery known to us.

Specification

The Geodata Discovery standard consists of following parts A and B (both in turn are based standards extensions, called substandards):

• Part A specifies two syndication formats and protocol extensions to OGCs WxS with specialized weblinks.
• Part B specifies how to use an icon in HTML webpages which links to syndication formats and protocols.

Part A (CONDITIONAL MANDATORY)

Specifies "See" and "See also" links (also called 'cross-links') in well known formats ("carrier formats") containing typified weblinks (whenever possible 'xlink' or "Atom link relation types") which provide semantics to help focussed crawlers to find OGC Services, like WMS, WFS, WCS, WPS and/or CSW.

Syndication format extensions:

• GeoRSS file format: Use of GeoRSS to syndicate KML content, similar to RSS support in HTML.. See the proposal here.
• Atom file format: rel and type attributes for See chap. 6.2

Syndication extensions to OGC Web Services, especially extensions of GetCapabilities request with xlink tags ... (tbd.)!

'CONDITIONAL MANDATORY' means that at least one of the thre mentioned substandards needs to implemented in order to comply to the "Geodata Discovery" standard.

Part B (OPTIONAL)

Specifies the placement of a Geotag icon (Microformat) in a HTML webpage. This is for human readability and trustworthiness as well as for general purpose webcrawlers (Google's principle of visual control) pointing to the syndication format (specified in Part A).

Compliance Tests

tbd. Ideally there should be a website which lists conformances tests given a website which was enhanced according to this specifications.

Background

At OGC there exists an interest group about discovery but there's no specification activity there yet.

This proposal does not compete with existing standards like CSW. In contrary, it is a supplement of those. It's the basis for better domain-specific search engines, like e.g. geocat.ch or geometa.info.

This proposal is based on own experiences and - among others - on the sources mentioned below.

References

Normative references:

• IETF Web Linking Draft (draft-nottingham-http-link-header-06) - Atom link relation types.
• XML Linking Language (XLink) Version 1.0.
• OpenSearch.org > OpenSearch Geo extension (Draft) - A leightweight harvesting interface (Remarks: "rel='search'" notifes an application that here is a service that it can query to get at additional resources. Applies often also to webapplications capable which can be called with Permalinks).
• CSW

Miscellaneous Weblinks:

• GeoWeb Standards – Discoverability from High Earth Orbit Blog, 2009-08-28.
• "Proposed standard for web linking" from Sean Gillies Blog, 2010-01-25.

History

• Version 1.00, 19.4.2010, Stefan Keller -- First release of the specification.