OSGeodata Discovery: Unterschied zwischen den Versionen
Aus Geoinformation HSR
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Before all we need a '''[[OSGeodata metadata exchange model| geographic metadata exchange model]]'''. Then we need a '''[[OSGeodata metadata exchange protocol| geographic metadata exchange protocol]]'''. | Before all we need a '''[[OSGeodata metadata exchange model| geographic metadata exchange model]]'''. Then we need a '''[[OSGeodata metadata exchange protocol| geographic metadata exchange protocol]]'''. | ||
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| + | [[Geo-Metadata| Metadata]] ... | ||
| + | * ... is just data about data, so nothing special regarding modeling and encoding | ||
| + | * ... according to metadata exchange model should be strictly free (LGPL?). | ||
| + | Links are for three things, (1) discovery (what pages exists), (2) reputation (how important is this page) and (3) annotation (what is this page about). | ||
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''. | 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''. | ||
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* Users need search services to discover geographic information. | * Users need search services to discover geographic information. | ||
| − | * Geodata owners need a metadata management tool (which implies an internal metadata model). | + | * [[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 | + | * [[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. |
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== Scenario == | == Scenario == | ||
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== Building blocks needed == | == Building blocks needed == | ||
# A geometadata management model ( e.g. internal to telascience) | # A geometadata management model ( e.g. internal to telascience) | ||
| − | # Tools to manage the | + | # Tools to manage the geo-metadata |
| − | # A geometadata exchange model | + | # A [[OSGeodata metadata exchange model| geometadata exchange model]] |
# An encoding of the geometadata exchange model (probably XML) | # An encoding of the geometadata exchange model (probably XML) | ||
| − | # Geometadata exchange protocols (see Discovery mechanisms and protocols) | + | # [[OSGeodata metadata exchange protocol| Geometadata exchange protocols]] (see chapter Discovery mechanisms and protocols) |
== Discovery mechanisms and protocols == | == Discovery mechanisms and protocols == | ||
Version vom 28. August 2006, 06:26 Uhr
Inhaltsverzeichnis
Need for geographic 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 geographic metadata exchange model. Then we need a geographic metadata exchange protocol.
Metadata ...
- ... is just data about data, so nothing special regarding modeling and encoding
- ... according to metadata exchange model should be strictly free (LGPL?).
Links are for three things, (1) discovery (what pages exists), (2) reputation (how important is this page) and (3) annotation (what is this page about).
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
"We don’t know what people will want to do, or how they will want to do it, but we may know how to allow people to do what they want to do when they want to do it". (ockham.org)
- 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.
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
- A geometadata management model ( e.g. internal to telascience)
- Tools to manage the geo-metadata
- A geometadata exchange model
- An encoding of the geometadata exchange model (probably XML)
- Geometadata exchange protocols (see chapter Discovery mechanisms and protocols)
Discovery mechanisms and protocols
We are aware of two types of 'protocols' both already implemented and ready to go (given an encoded information according to a well specified model):
- Autodiscovery: Publish XML files of geometadata (exchange model) on the web (=HTTP).
- Registry: 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 for augmented autodiscovery. See also THUMP from IETF which leads to something between 1. and 2.
About autodiscovery:
- Pull principle.
- Requires at least one relation - an URL or a tag like a class.
- Uses UI to point to content-rich XML-encoded feed, therefore crosses from human mode to machine mode, in a way that’s easy for both humans and machines.
- Autonomous/independent resource owner; no further action required from him.
- Possible use of links/relations to point to (master) whole collection of resources (including pointers to these, like microformats.org.
- Examples: (X)HTML pages, Extended and XML encoded Dublin Core.
About registry:
- Push principle.
- More load on resource owner.
- Awareness and action required from resource owner.
- Examples: OAI-PMH, RSS pinging search services...
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, ...?
