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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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See also:
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Allow to '''[[OSGeodata Discovery| discover geodata]]'''! Let's make metadata 'sexy' again.
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* [[OSGeodataMetadataModel]] for a proposal of an information model (e.g. for response data).
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* [http://wiki.osgeo.org/index.php/Geodata_Metadata_Requirements#Discovery Wiki at osgeo.org] for requirements
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For the '''[[OSGeodata Discovery| discovery of geodata]]''' we need a
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* [https://geodata.osgeo.org/servlets/BrowseList?listName=geodata geodata Mailing list at osgeo.org] for discussions
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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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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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Keywords: Open access to and dissemination of geographic data (geodata) and information; Metadata; Finding, harvesting or discovery of geodata and web map services; service binding.  
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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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Appropriate name sought for a protocol:
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== Pleadings for metadata (models) and adequate protocols ==
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* geographic metadata protocol
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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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* geographic metadata harvesting protocol
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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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* geographic data dissemination protocol
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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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* ?
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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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* [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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* Paper "Are Geospatial Catalogues Reaching their Goals?" from [http://www.agile2006.hu/papers/Larson_Siliceo_etal.pdf Larson et al.].
  
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== Comparison between WFS and OAI-PMH ==
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== Building blocks for metadata management ==
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Building blocks are:
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# A geometadata '''management model''' (e.g. internal to each organisation)
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# '''Tools''' to manage the geometadata
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# A geometadata '''[[OSGeodata metadata exchange model| exchange model]]'''
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# An '''encoding''' of the geometadata exchange model (probably XML)
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# Geometadata '''[[OSGeodata metadata exchange protocol| exchange protocols]]''' (like [[OAI-PMH]], see [[OSGeodata_Discovery]])
  
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Relative (biased?) comparison:
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== Weblinks ==
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* OAI-PMH is a set of simple and strictly RESTful harvesting protocols based on Dublin Core (since 1995) whereas WFS allows a RESTful or SOAP client to retrieve geospatial data encoded in GML (since 2000).
 
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* WFS though originated in GIS covers a smaller community than OAI-PMH which today has a larger user base and is supported even by Google and Yahoo!.
 
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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 ~200 p.) whereas OAI-PMH needs probably to be extended (spec. size is ~50 p.) - so WFS seems more complex and more costly to implement or adapt but much depends on the needs (make sophisticated queries vs. harvesting?) and underlying the architecture (distributed online services vs. local indexing).
 
  
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=== WFS ===
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Information:
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* WFS is short for 'Web Feature Service'.
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* [http://wiki.osgeo.org/index.php/Geodata_Metadata_Requirements#Discovery Wiki at osgeo.org] for requirements
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* Spec. size: About 100 pages plus mandatory reference to Filter spec. of about 40 pages, plus reference to GML 2 (60 pages).
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* [https://geodata.osgeo.org/servlets/BrowseList?listName=geodata Geodata mailing list at osgeo.org] for discussions
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* Background: A de-facto standard in GIS world owned by OGC
 
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* Request operations (Basic WFS, read only WFS):
 
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** ''GetCapabilities'' - describe service capabilities;
 
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** ''DescribeFeatureType'' - describe structure of a feature type
 
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** ''GetFeature'' - retrieve feature instances
 
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* Query:
 
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** Standard query (c.f. Filter) includes spatial constraints (but no temporal?)
 
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* Response:
 
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** Must be GML 2 and may be other XML encodings.
 
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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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* 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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* Spec. size: < 50 pages(!) plus??
 
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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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* Request operations:
 
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** ''Identify'' - describe an archive (similar to WFS' GetCapabilities)
 
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** ''ListMetadataFormats'' - retrieve available metadata formats from archive
 
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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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** ''ListSets'' - retrieve set structure of a repository (optional)
 
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* Query:
 
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** Standard query includes temporal constraints (but no spatial yet).
 
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* Response:
 
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** Either an encoded error or unqualified Dublin Core XML or another format announced with ListMetadataFormats.
 
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* Peculiarities:
 
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** For identifiers URI must be used (similar requirement to WFS).
 
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** Has no version negotiation (but see operation Identify)
 
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** Knows incremental update
 
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** Another spec. was released called 'OAI Static Repository and an OAI Static Repository Gateway'
 
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** OAI-PMH may respond results in compressed form which is handled at the HTTP-level (how RESTful!)
 
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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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** ...?
 
  
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== Weblinks ==
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<!-- Kategorien und ev. Koordinaten -->
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* OGC's CSW 2.0
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[[Kategorie: Geodaten]] [[Kategorie: Metadaten]] [[Kategorie: English]]
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* OGC's WFS
 
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* [http://www.openarchives.org/OAI/openarchivesprotocol.html OAI-PMH] - Open Archives Initiative Protocol for Metadata Harvesting 2.0
 

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»