ESA Workshop

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• OGC Catalogue Services
• and Profiles
• -
• Experiences in defining a profile
• Kristian Senkler
• senkler_at_conterra.de

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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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Backgrund information

• Problem (nearly) each federal state in Germany
  has its own SDI Initiative
• Different requirements on catalogue services
• Different requirements on metadata
• 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
• Main (common) aspects of this agreement gave
  input to the ISO profile
• National requirements were not considered in
  the specification
• Goal Specification Implementation of an ISO
  profile for catalogue service in Germany

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The Principle of Profiles
base spec
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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 10000-11998.

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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.

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Catalog Application Profile General structure

• System context
• Application domain
• Essential use cases
• Information models
• Capability classes
• Catalogue information model
• Supported data bindings
• Service information model
• Native language support

• External interfaces
• Imported protocol bindings
• Interface A, B,
• Query facilities
• General implementation guidance
• Security considerations

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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.

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Information models Catalogue information model

• The CSW information model ISO 191152003 and ISO
  191192005.
• ISO 191152003 specifies a model for (data)
  metadata descriptions.
• ISO 191192005 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
• 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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Information models Catalogue information model

• Mapping OGC core queryable properties
• Maps the core queryables to information model of
  the profile
• Mapping OGC core returnable properties
• Maps OGC core returnable properties and
  properties defined by the profile
• Definition and mapping of additional search
  properties
• Additional properties coming from ISO model (e.g.
  TopicCategory or ServiceType)

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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 ISO191192005 (with extensions) has been
  developed.
• ? Amendment to ISO 191192005

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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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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.

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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)
• admit multiple programming language bindings
• show error conditions that can occur

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Experiences Problems - Specification

• ISO 19115/19119 can be applied in a variety of
  use cases
• Problem of not having ISO 19139 v1.0 ready by
  now
• CS-W Interfaces are sufficient
• Accuracy of standard ! accuracy of metadata
  producer
• spatial extent
• freetext elements
• Keywords are only useful if they come from a
  thesaurus

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Experiences Problems - Implementation

• Problem with encoding of XML documents
• UTF-8 is the standard encoding for metadata
  documents. This often leads to wrong
  interpretation of German Umlauts, if you dont
  handle UTF-8 correctly (e.g. missing Byte Order
  Mark).
• Problem with datum
• ISO 8601 is sometimes misinterpreted (e.g.
  2005-9-27T113621)
• Some crucial parts in ISO 19115/19119
• Language (ISO 639-2, but others are possible)
• Codelists
• Accuracy of spatial coordinates
• Misinterpretation of specification
• Case-sensitive parameters
• Wrong bindings

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Technical Experiences Problem

• XML-Data binding frameworks (e.g. SUNs JAXB)
• Very strict in marshalling/unmarshalling
  documents
• Very strict in document encoding.
• Does not distinguish between valid or
  incomplete documents
• Distributed search
• Its difficult to calculate hits in a specific
  network topology
• Its more difficult, if you start to sort hits
  by date, title or something
• Its 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

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• Thank you very much!
• senkler_at_conterra.de