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OGC Catalogue Services and Profiles-Experiences in defining a profile

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					OGC Catalogue Services
and Profiles
Experiences in defining a profile

Kristian Senkler senkler@conterra.de

...connecting worlds

ESA Workshop 28.10. 2005

Contents
Background information

Principles of Profiles
Catalog Application Profile
General aspects General structure

Application domain
Information models External interfaces

Experiences & Problems
Specification
Implementation

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ESA Workshop 28.10. 2005

Backgrund information
Problem: (nearly) each federal state in Germany has its own SDI Initiative

o Different requirements on catalogue services o Different requirements on metadata o Existing implementations on different levels
Established a working group with participant from all federal states to find a mutual agreement on metadata and catalogue services

o Main (common) aspects of this agreement gave input to the ISO
profile

o National requirements were not considered in the specification
Goal: Specification & Implementation of an ISO profile for catalogue service in Germany

...connecting worlds

ESA Workshop 28.10. 2005

The Principle of Profiles
Query language Core queryables base spec bindings

Profile A

Profile B

Informationmodel_A
Interfaces_A Binding_A

Informationmodel_B
Interfaces_B Binding_B

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ESA Workshop 28.10. 2005

The Principle of Profiles
Purpose: specify the use of sets of specifications to provide clearly defined functionality. Hence, conformance to profile specification implies conformance to referenced specification. A profile identifies the use of particular options available in one or more base standards and it also provides a basis for developing conformance tests. A general framework for profile specification is defined by ISO/IEC TR 10000-1:1998.

...connecting worlds

ESA Workshop 28.10. 2005

Catalog Application Profile – General aspects
An application profile specifies a set of functional components that are provided by a conforming implementation and binds them to an abstract information model (providing one or more concrete representations of catalogue content).
Each representation is an Internet media type that conforms to a schema defined using some schema language (e.g., ASN.1, XML Schema, RDF Schema).

An application profile specifies the use of an application-layer protocol in order to provide a structured transfer of information between systems.

P latform neutral sp ec base specification

1..* co m p liesW ith

P latform sp ecific sp ec

1..* co nform sT o catalogue implementation
ESA Workshop 28.10. 2005

application profile + protocol binding

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Catalog Application Profile – General structure
System context
Application domain
Essential use cases

External interfaces
Imported protocol bindings
Interface A, B, … Query facilities General implementation guidance

Information models
Capability classes
Catalogue information model Supported data bindings Service information model Native language support

Security considerations

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ESA Workshop 28.10. 2005

System context - Application domain
Focus on metadata about geospatial data, services and applications.

The profile does not attempt to specify a general-purpose catalogue.
The profile has no specific disciplinary focus. All communities working with these sorts of information resources are addressed. The intention is to implement a generally understood information model based on standard metadata with only a few relationships among the catalogue items. The profile allows for a catalogue to accept a request from a client and distribute the request to one or more other catalogues within a federation.

It is possible to start a search from only one known location and to search as many catalogues as possible with the same set of attributes.

...connecting worlds

ESA Workshop 28.10. 2005

Information models – Catalogue information model
The CSW information model ISO 19115:2003 and ISO 19119:2005.

o
o

ISO 19115:2003 specifies a model for (data) metadata descriptions. ISO 19119:2005 specifies a model for service metadata descriptions.

The main purpose of the information model is to provide a formal structure for the description of information resources that can be managed by a catalogue service

Information resources manage by ISO catalogue

o o o o

Dataset: An identifiable collection of data Dataset series: A collection of datasets sharing the same product specification Services: A service instance hosted on a specific set of hardware and accessible over a network. A service is tightly coupled, loosely coupled or mixed coupled. Application: An resource that is hosted on a specific set of hardware and accessible over a network.

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ESA Workshop 28.10. 2005

Information models – Catalogue information model
Dublin Core metadata element name dc:language Term used in application profile Language Property Mapping to Information Model

MD_Metadata.identificationInfo.MD_DataIdentification.language

Mapping OGC core queryable properties

o

Maps the core queryables to information model of the profile

Mapping OGC core returnable properties

o Maps OGC core returnable properties and properties defined by
the profile

Definition and mapping of additional search properties

o Additional properties coming from ISO model (e.g. TopicCategory
or ServiceType)

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ESA Workshop 28.10. 2005

Information models – Supported data bindings
Only XML is supported.

XML encoding is based on ISO19139 v0.9.
 This will be updated to ISO19139 v1.0 as soon as this version is adopted by ISO.

In case of dataset, dataset series and application, no further extensions had to made. In case of services, an XML Schema in accordance to ISO19119:2005 (with extensions) has been developed.
 Amendment to ISO 19119:2005

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ESA Workshop 28.10. 2005

Information models – Supported element sets
Brief: brief information about a located resource

Summary: summary information, equivalent to ISO Core elements (ISO19115 plus ISO19119)
Full: full representation of a located resource

plus, of course, core result sets given by CSW 2.0 base specification.

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ESA Workshop 28.10. 2005

External interfaces - Imported Protocol Binding
Profile imports the HTTP protocol binding from the CSW specification All of the CSW(T) ISO operations have a corresponding CSW operation. The table summarises the CSW(T) ISO operations and their encoding methods that are applied in this profile.
CSW(T) Operation GetCapabilities DescribeRecord GetDomain GetRecords GetRecordById HarvestRecords Transaction Request encoding XML(POST+SOAP) and KVP (GET) XML (POST+SOAP) and KVP (GET) XML (POST+SOAP) and KVP(GET) XML (POST+SOAP) and KVP(GET) XML (POST+SOAP) and KVP(GET) XML (POST+SOAP) and KVP(POST) XML (POST+SOAP)

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ESA Workshop 28.10. 2005

External interfaces - Interface specifications
Describes syntax and semantics restrictions and variations of the interface operations in comparison to those of the imported CSW 2.0 (with Corrigendum) HTTP protocol binding. It gives formal, language-independent interface specifications (W3C WSDL)

o admit multiple programming language bindings o show error conditions that can occur

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ESA Workshop 28.10. 2005

Experiences & Problems - Specification
ISO 19115/19119 can be applied in a variety of use cases

o Problem of not having ISO 19139 v1.0 ready by now
CS-W Interfaces are sufficient Accuracy of standard != accuracy of metadata producer

o spatial extent o freetext elements
Keywords are only useful if they come from a thesaurus

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ESA Workshop 28.10. 2005

Experiences & Problems - Implementation
Problem with encoding of XML documents

o

UTF-8 is the standard encoding for metadata documents. This often leads to wrong interpretation of German Umlauts, if you don‘t handle UTF-8 correctly (e.g. missing Byte Order Mark).

Problem with datum

o

ISO 8601 is sometimes misinterpreted (e.g. 2005-9-27T11:36:21)

Some crucial parts in ISO 19115/19119

o o o

Language (ISO 639-2, but others are possible) Codelists Accuracy of spatial coordinates

Misinterpretation of specification

o
o o

Case-sensitive parameters Wrong bindings …
ESA Workshop 28.10. 2005

...connecting worlds

Technical Experiences & Problem
XML-Data binding frameworks (e.g. SUN‘s JAXB)

o Very strict in marshalling/unmarshalling documents
o Very strict in document encoding. o Does not distinguish between valid or incomplete documents
Distributed search

o It‘s difficult to calculate hits in a specific network topology
o It‘s more difficult, if you start to sort hits by date, title or
something

o It‘s most difficult, when a client starts to browse theses
results.

 infinite recursion: hopCount = 1 (limited number of cataloges by
now)

 double hits: UUID as fileIdentifier

...connecting worlds

ESA Workshop 28.10. 2005

Thank you very much!
senkler@conterra.de

...connecting worlds

ESA Workshop 28.10. 2005


				
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