Y. Coene, Spacebel Frascati, 28 october 2005

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Service Discovery based on Standards

• Y. Coene, SpacebelFrascati, 28 october 2005

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Overview

• Problem
• Service registries for SOA
• Standards
• Ws-inspection
• UDDI
• OGC CSW
• RSS
• A real case the Service Support Environment
• Conclusions

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Problem

• Challenges
• Discover (Web) services available in SOA
• Discover composite services (workflows) available
  in SOA
• Allow access from (commercial) service
  orchestration tools
• Support Application to Application (A2A)
  interactions

• IT Challenges
• Use simple, standard technologies that partners
  can easily adopt
• Multiple competing standards UDDI, ws-inspection,
  OGC CSW
• Support in COTS needed to limit cost

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Service Registry

• Key component of a SOA architecture
• Loosely coupled services
• Service discovery and documentation
• Evolution to also contain policy, governance and
  security info.

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WS-Inspection Language

• WSIL (IBM, Microsoft)
• Simple protocol
• Registry is a single XML file with references
  residing in fixed place
• Points to WSDL end-points
• Limited industry support (IBM, Microsoft, Oracle,
  ...)
• Some public registries Xmethods, ...
• Not supported by a standardisation body

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WS-Inspection Language

• WSIL
• Supported by COTS tools such as Eclipse BPEL
  Designer to build workflows

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OASIS UDDI

• Defines protocols for
• Publishing and searching services registry
• Controlling access to registry
• Distributing and delegating to other registries

UDDI RegistryNode
Client
UDDISOAP Request
HTTPServer
SOAPProcessor
UDDISOAP Response
UDDIRegistry Service
Create, View, Update, and Deleteregistrations
Service Directory
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OASIS UDDI
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OASIS UDDI

• Managed by OASIS (BPEL, SAML, WS-Security etc.)
• Widely adopted, public registries exist
• Commercial and open-source registry software
  available Infravio, Systinet, JUDDI, ...
• Core Web service standard according to IT
  analysts (Gartner)

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OASIS UDDI

• Supported by commercial Web service development
  tools

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Open Geospatial Consortium

• OGC CSW
• Registry for data and services
• Mainly for OGC services, not related to WSDL
• GetCapabilities() allows to discover supported
  (catalogue) operations
• Calls service.GetCapabilities() to harvest
  metadata
• Many profiles, bindings reduce interoperability
• Still maturing in OWS-3 experiments (ebRIM)
• Not supported by main Web service and BPM tool
  vendors

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Syndication Formats

• Atom (IETF) and RSS (Really Simple Syndication)
• Related to RDF (W3C)
• Two use cases
• Meta-data (news) feeds exist for new books, music
  etc. in a library. Typically small chunks of
  info.
• Amazon.com search results in RSS format
• Discover new images/services in an EO catalogue?
• Only suitable when limited quantity of items
  published per day.
• Many clients available, allowing for syndication
  (i.e. combination of data channels)

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DISCO

• Similar approach as WSIL
• Microsoft specification (XML)
• Service Discovery for .NET
• Single document with links to .XSDL files
• DISCO file understood by Visual Studio

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Service Discovery in SSE
Service Partner C
Service Partner B
Service Partner A
Network of service partners
BPEL Solution
Management Console
Design
Oracle BPEL PM
Engine
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Standard "Pull" Strategy

• W3C
• SOAP, WSDL, XML Schema, ws-addressing
• OASIS
• BPEL
• OGC
• GML, WMS, WMS-context
• WCS, WCTS (from BPEL)
• Other
• Alexandria gazetteer
• Ws-inspection
• RSS, WSIF
• WS-I (Basic Profile)

• Also planned or considered
• OGC WFS
• OGC CSW (client)
• OGC Gazetteer
• LDAP, SAML
• Ws-security, UDDI
• RDF, RDFS, OWL, OWL-S
• Google KML

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Service Discovery in SSE

• WSIL Registry at services.eoportal.org
• Includes links to service WSDL files
• Accessible from Eclipse BPEL Designer
• UDDI Registry v2 (JUDDI) to be available soon.
• With organisations
• With services and their WSDL file
• Accessible from JDeveloper BPEL Designer
• Issue with service taxonomy

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Service Discovery in SSE

• Interface with OGC CSW for discovery and storage
  of WMS services
• WMS layers as background for service results
• Not planned but feasible
• Services currently taken from a configuration file

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Conclusion

• Several open questions
• Which "standards" or "profiles" to be used to be
  interoperable ?
• Data and services to be dealt with same standard
  ?
• Service taxonomy interoperability ?

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Conclusion

• Selection criteria for "service discovery" spec
• In-line with main IT standards for Web services
• If multiple profiles, bindings or non-compatible
  versions a single choice is to be made.
• Allow use of cheap COTS for development and
  deployment
• Should allow non-intrusive addition of identity
  mgt, Web service management and policy
  inforcement COTS
• Should be understood by service chaining COTS

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Service Discovery in SSE

• More info
• http//services.eoportal.org
• Pier.Giorgio.Marchetti_at_esa.int (technical
  officer)
• yves.coene_at_spacebel.be