OSGeodata: Unterschied zwischen den Versionen
Aus Geoinformation HSR
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Experimental pages for OSGeodata Mailing List on [https://geodata.osgeo.org/servlets/BrowseList?listName=geodata&by=date&paged=false OSGeo.org]. | Experimental pages for OSGeodata Mailing List on [https://geodata.osgeo.org/servlets/BrowseList?listName=geodata&by=date&paged=false OSGeo.org]. | ||
− | == Goal == | + | == Goal for a lean and mean geographic metadata protocol == |
Citation from Jo Walsh: "Managing metadata well is the key to making a repository of open geographic data really useful and re-usable. Creating metadata can be a dull chore. Part of the problem is over-focus on production, rather than consumption; on standards, rather than on usage. The Geodata Committee at OSGeo has been working on a "simplest useful thing" approach to geographic metadata...". | Citation from Jo Walsh: "Managing metadata well is the key to making a repository of open geographic data really useful and re-usable. Creating metadata can be a dull chore. Part of the problem is over-focus on production, rather than consumption; on standards, rather than on usage. The Geodata Committee at OSGeo has been working on a "simplest useful thing" approach to geographic metadata...". |
Version vom 4. August 2006, 11:07 Uhr
Experimental pages for OSGeodata Mailing List on OSGeo.org.
Inhaltsverzeichnis
Goal for a lean and mean geographic metadata protocol
Citation from Jo Walsh: "Managing metadata well is the key to making a repository of open geographic data really useful and re-usable. Creating metadata can be a dull chore. Part of the problem is over-focus on production, rather than consumption; on standards, rather than on usage. The Geodata Committee at OSGeo has been working on a "simplest useful thing" approach to geographic metadata...".
See also: OSGeodataMetadataModel.
Comparison between WFS and OAI-PMH
Relative (biased?) comparison:
- OAI-PMH is a set of simple harvesting protocols based on Dublin Core (since 1995) whereas WFS allows a client to retrieve geospatial data encoded in GML (since 2000).
- WFS though originated in GIS could cover a smaller community than OAI-PMH which today probably has a larger user base and is supported even by Google.
- Both have in common that they can be made (WFS) or are (OAI-PMH) RESTful and both can be profiled to respond an 'output content model' - which has yet to be defined (see OSGeodataMetadataModel).
- WFS needs to be profiled (spec. size is > 140 p.) whereas OAI-PMH needs probably to be extended (spec. size is < 50 p.) - so WFS seems more complex and more costly to implement.
WFS
- WFS is short for 'Web Feature Service'.
- Spec. size: About 100 pages plus at least refernce to Filter spec. of about 40 pages, plus ??.
- Background: A de-facto standard in GIS world owned by OGC
- Request operations (Basic WFS, read only WFS):
- GetCapabilities - describes service capabilities;
- DescribeFeatureType - descibes structure of a feature type
- GetFeature - retrieves feature instances
- Query:
- Standard query includes spatial constraints (but no temporal?)
- Peculiarities:
- Knows version negotiation (which isn't implemented yet...)
- Uses URN as unique identifier
- Availability and outreach of services, tools and (open source) software:
- Open source software see freegis.org
- Expected changes to spec. (profile or extension):
- Profile to KVP binding
- Profile Filter to Boolean and Wildcard matches as well as 'within'
- ...
OAI-PMH
- OAI is short for 'Open Archives Initiative', PMH is short for 'Protocol for Metadata Harvesting'.
- Spec. size: < 50 pages(!) plus??
- Background: Was initiated by libraries, universities, museums and galleries to 'open access' (OA) free online availability of digital content.
- Request operations:
- Identify - describe an archive (similar to WFS' GetCapabilities)
- ListMetadataFormats - retrieve available metadata formats from archive
- ListSets - retrieve set structure of a repository
- ListIdentifiers - abbreviated form of ListRecords, retrieving only headers
- ListRecords - harvest records from a repository (similar to WFS' GetFeature)
- GetRecord - retrieve individual metadata record from a repository (also similar to WFS' GetFeature)
- Query:
- Standard query includes temporal constraints (but no spatial).
- Peculiarities:
- Uses identifier mechanism (numbers) from digital archives.
- Has no version negotiation
- Availability and outreach of services, tools and (open source) software:
- Open source software see OAI-PMH tools
- Gateways available from publishing files to others
- Google reads it as a Sitemaps file (how to submit) and Internet Archive uses it among others.
- Expected changes to spec. (profile or extension):
- special treatment of ID's?
- Need to be extended if spatial constraints are needed here
- Add version negotiation?
- ...?
Weblinks
- OGC's CSW 2.0
- OGC's WFS
- OAI-PMH - Open Archives Initiative Protocol for Metadata Harvesting 2.0