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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].
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== Overview ==
  
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== Goal for a lean and mean geographic metadata protocol ==
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These are experimental pages ([[OSGeodata Discovery|1]],[[OSGeodata metadata exchange model|2]],[[OSGeodata metadata exchange protocol|3]],[[OAI-PMH|4]]) originated from OSGeodata Mailing List on [https://geodata.osgeo.org/servlets/BrowseList?listName=geodata&by=date&paged=false OSGeo.org].
  
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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...".
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Let's unleash geographic information through open access and dissemination of geographic data and (metadata) search appliances!
  
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Appropriate name sought:
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Allow to '''[[OSGeodata Discovery| discover geodata]]'''! Let's make metadata 'sexy' again.
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* geographic metadata protocol
 
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* geographic metadata harvesting protocol
 
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* ?
 
  
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See also: [[OSGeodataMetadataModel]].
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For the '''[[OSGeodata Discovery| discovery of geodata]]''' we need a
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* '''[[OSGeodataMetadataModel| Geographic metadata exchange model]]''' as well as a
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* '''[[OSGeodataMetadataProtocol| Geographic metadata exchange protocol]]''' (catalog service).  
  
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== Comparison between WFS and OAI-PMH ==
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For '''documentation''' an internal geodata management model is needed. For the '''metadata metadata exchange model''' a proposal was made called  '''[http://wiki.osgeo.org/index.php/Geodata_Metadata_Requirements#Information_model_for_metadata_exchange Dublin Core lite for Geo (DClite4G)]'''.
  
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Relative (biased?) comparison:
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Remarks: '''Metadata''' is just data about data. There is nothing special regarding its modeling and encoding. Metadata according to metadata exchange model should be strictly free (LGPL?).
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* 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).
 
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* 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.
 
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* 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]]).
 
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* 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.
 
  
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=== WFS ===
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== Pleadings for metadata (models) and adequate protocols ==
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* WFS is short for 'Web Feature Service'.  
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* ''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)
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* Spec. size: About 100 pages plus at least refernce to Filter spec. of about 40 pages, plus ??.
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* [http://www.digitalearth.com.au/2006/06/23/lightweight-web-resource-catalogue/ Blog 1] - "Leight Weight Web Resource Catalogue"
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* Background: A de-facto standard in GIS world owned by OGC
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* [http://geotips.blogspot.com/2006/02/more-simple-web-services-catalogues.html Blog 2] - More Simple Web Services Catalogues...", and  
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* Request operations (Basic WFS, read only WFS):
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* [http://www.kralidis.ca/blog/2006/08/04/geospatial-catalog-development-brewing/ Blog 3] - geospatial-catalog-development-brewing.
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** ''GetCapabilities'' - describes service capabilities;  
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* [http://home.badc.rl.ac.uk/lawrence/blog/all Bryan's Blog]: "To extend or not to extend ..." ("In practice, we can exchange any derivative of the ISO19139 profiles using OAI and store them in xml databases.").
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** ''DescribeFeatureType'' - descibes structure of a feature type
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* Paper "Are Geospatial Catalogues Reaching their Goals?" from [http://www.agile2006.hu/papers/Larson_Siliceo_etal.pdf Larson et al.].
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** ''GetFeature'' - retrieves feature instances
 
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* Query:
 
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** Standard query includes spatial constraints (but no temporal?)
 
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* Peculiarities:
 
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** Knows version negotiation (which isn't implemented yet...)
 
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** Uses URN as unique identifier
 
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* Availability and outreach of services, tools and (open source) software:
 
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** Open source software see [http://www.freegis.org freegis.org]
 
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* Expected changes to spec. (profile or extension):
 
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** Profile to KVP binding
 
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** Profile Filter to Boolean and Wildcard matches as well as 'within'
 
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** ...
 
  
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=== OAI-PMH ===
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== Building blocks for metadata management ==
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* OAI is short for [http://en.wikipedia.org/wiki/Open_Archives_Initiative 'Open Archives Initiative'], PMH is short for 'Protocol for Metadata Harvesting'.  
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Building blocks are:
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* Spec. size: < 50 pages(!) plus??
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# A geometadata '''management model''' (e.g. internal to each organisation)
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* Background: Was initiated by libraries, universities, museums and galleries to 'open access' (OA) free online availability of digital content.
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# '''Tools''' to manage the geometadata
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* Request operations:
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# A geometadata '''[[OSGeodata metadata exchange model| exchange model]]'''
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** ''Identify'' - describe an archive (similar to WFS' GetCapabilities)
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# An '''encoding''' of the geometadata exchange model (probably XML)
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** ''ListMetadataFormats'' - retrieve available metadata formats from archive
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# Geometadata '''[[OSGeodata metadata exchange protocol| exchange protocols]]''' (like [[OAI-PMH]], see [[OSGeodata_Discovery]])
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** ''ListSets'' - retrieve set structure of a repository
 
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** ''ListIdentifiers'' - abbreviated form of ListRecords, retrieving only headers
 
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** ''ListRecords'' - harvest records from a repository (similar to WFS' GetFeature)
 
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** ''GetRecord'' - retrieve individual metadata record from a repository (also similar to WFS' GetFeature)
 
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* Query:
 
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** Standard query includes temporal constraints (but no spatial).
 
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* Peculiarities:
 
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** Uses identifier mechanism (numbers) from digital archives.
 
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** Has no version negotiation
 
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* Availability and outreach of services, tools and (open source) software:
 
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** Open source software see [http://www.openarchives.org/tools/tools.html OAI-PMH tools]
 
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** Gateways available from publishing files to others 
 
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** Google reads it as a Sitemaps file ([http://www.google.com/support/webmasters/bin/answer.py?answer=34655 how to submit]) and Internet Archive uses it among others.
 
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* Expected changes to spec. (profile or extension):
 
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** special treatment of ID's?
 
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** Need to be extended if spatial constraints are needed here
 
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** Add version negotiation?
 
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** ...?
 
  
 
== Weblinks ==
 
== Weblinks ==
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* OGC's CSW 2.0
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* OGC's WFS
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Information:
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* [http://www.openarchives.org/OAI/openarchivesprotocol.html OAI-PMH] - Open Archives Initiative Protocol for Metadata Harvesting 2.0
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* [http://wiki.osgeo.org/index.php/Geodata_Metadata_Requirements#Discovery Wiki at osgeo.org] for requirements
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* [https://geodata.osgeo.org/servlets/BrowseList?listName=geodata Geodata mailing list at osgeo.org] for discussions
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<!-- Kategorien und ev. Koordinaten -->
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[[Kategorie: Geodaten]] [[Kategorie: Metadaten]] [[Kategorie: English]]

Aktuelle Version vom 29. Oktober 2006, 12:15 Uhr

Overview

These are experimental pages (1,2,3,4) originated from OSGeodata Mailing List on OSGeo.org.

Let's unleash geographic information through open access and dissemination of geographic data and (metadata) search appliances!

Allow to discover geodata! Let's make metadata 'sexy' again.

For the discovery of geodata we need a

For documentation an internal geodata management model is needed. For the metadata metadata exchange model a proposal was made called Dublin Core lite for Geo (DClite4G).

Remarks: Metadata is just data about data. There is nothing special regarding its modeling and encoding. Metadata according to metadata exchange model should be strictly free (LGPL?).

Pleadings for metadata (models) and adequate protocols

  • 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)
  • Blog 1 - "Leight Weight Web Resource Catalogue"
  • Blog 2 - More Simple Web Services Catalogues...", and
  • Blog 3 - geospatial-catalog-development-brewing.
  • Bryan's Blog: "To extend or not to extend ..." ("In practice, we can exchange any derivative of the ISO19139 profiles using OAI and store them in xml databases.").
  • Paper "Are Geospatial Catalogues Reaching their Goals?" from Larson et al..

Building blocks for metadata management

Building blocks are:

  1. A geometadata management model (e.g. internal to each organisation)
  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 (like OAI-PMH, see OSGeodata_Discovery)

Weblinks

Information:

Von «https://giswiki.hsr.ch/index.php?title=OSGeodata&oldid=3964»