OSGeodata Discovery: Unterschied zwischen den Versionen

Version vom 23. August 2006, 01:08 Uhr

Need for a model and a protocol for metadata exchange

Geographic catalog (catalog service) or inventory are rather data provider centric names, so we prefer a user centric approach. See also OSGeodata for further discussion.

Before all we need a metadata exchange model. Then we need a metadata exchange protocol.

Keywords: Open access to and dissemination of geographic data (geodata) and information; Metadata; Finding, harvesting or discovery of geodata and web map services; Interoperability; Integration; Service binding; Spatial data infrastructure; Standards.

Vision

• Users need search services to discover geographic information.
• Geodata owners need a metadata management tool (which implies an internal metadata model).
• Geodata owners and service providers need (i) a metadata exchange model, (ii) an encoding of it, as well as (iii) a protocol for the exchange, dissemination and sharing of metadata.

Remarks: Metadata ...

• Metadata is just data about data, so nothing special regarding modeling and encoding
• Metadata should be strictly free (LGPL?).

Scenario

A preliminary scenario:

• Users search or browse through metadata records. They use a web app. or a search component out of a desktop GIS (remark: Users don't search services per se).
• 'Search service providers' enable the discovery of geodata and 'filter services', like transformation services (Note: WMS is a 'data access service' and belongs to geodata not to filter services)
• 'Search service providers' gather (harvest) their information from 'data/filter service providers' and need a protocol to do this.
• 'Data/filter service providers' offer metadata over this protocol. They typically also implement 'data access services' (WMS, WFS) or they offer 'filter services'.

Building blocks needed

1. A geometadata management model ( e.g. internal to telascience)
2. Tools to manage the geometadata
3. A geometadata exchange model
4. An encoding of the geometadata exchange model (probably XML)
5. Geometadata exchange protocols

We see two specifications, both already implemented and ready to go (given 3. and 4. are determined!):

1. Simply publish XML files of geometadata (exchange model) on the web (=HTTP, autodiscovery).
2. OAI-PMH which uses geometadata exchange model as its specialized metadata model type (data providers needed to register but search services can do better focussed crawling).

There are some ideas around like embedding hints into the geometadata exchange model or THUMP from IETF which lead to something between 1. and 2.

Weblinks

Geographic information search services:

• Catalogs:
  • mapdex.org
  • ESRI's geography network
  • National Portals: US, CA, EU, UK, FR, DE, AT, CH
• Search engines:
  • General: Google Maps, MSN live, Yahoo!
  • Specialized: geometa.info (still german only for linguistic processing reasons)
• GIS with catalog and search components:
  • uDig, ArcGIS, ...?