A Mediated Approach towards Web Service Choreography

1
A Mediated Approach towards Web Service
Choreography

• Michael Stollberg, Dumitru Roman, Juan Miguel
  Gomez
• DERI Digital Enterprise Research Institute
• first.last_at_deri.org
• Semantic Web Services Preparing to Meet the
  World of Business Applications (ISWC 2004
  Workshop)

2
Problem Setting

• promise of Web Services as next generation EAI
  technology
• a functionality for integrating something
• can be arbitrarily combined
• have a seamless usage interface
• semantic technologies allow more sophisticated
  support for this than the current Web Service
  tech stack
• gt what is needed and how shall it work ?

3
Overview what we aim at

• The Choreography of a Web Service defines its
  usage interface
• A Global Model defines how several Web Service
  interact to achieve a common business goal
• Usage of Mediators to resolve possibly occurring
  mismatches between the Choreographies of Web
  Services participating in a Global Model
• A Semantic Web Service solution for the
• Web Service promise ?

4
WSMO Web Service Description

• complete item description
• quality aspects
• Web Service Management

• Advertising of Web Service
• Support for WS Discovery

Capability functional description
Non-functional Properties Core WS-specific

• Realization of WS by using
• other Web Services
• Functional
• decomposition
• WS
• Composition

Web Service Implementation (not of interest in
Web Service Description)

• Interaction Interface
• for consuming WS
• Messages
• External Visible
• Behavior
• Grounding

Orchestration
Choreography --- Interfaces ---
5
Choreography in WSMO

• Interface of Web Service for client-service
  interaction when consuming the Web Service
• Aspects
• 1) Choreography Interaction Interface of a Web
  Service
• 2) Global Model multiple Web Services
  collaboration
• 3) Choreography Mediation establish valid
  Choreographies

6
Choreography Aspects
under construction

• External Visible Behavior
• those aspects of the workflow of a Web Service
  where User Interaction is required
• described by process / workflow constructs
• Communication Structure
• messages sent and received
• their order (messages are related to activities)
• Choreography Grounding
• concrete communication technology for interaction
  
• choreography related errors (e.g. input wrong,
  message timeout, etc.)
• related to WS behavior descriptions, e.g. WSCI,
  BPEL4WS

7
Choreography Formal Model
under construction

• Formalization needed to allow operations /
  mediation on WSMO Choreography Interfaces
• Formal Basis Abstract State Machines (ASM)
• ASM consists of Constants and Transition Rules
  all Transition Rules are executed simultaneously
  according to conditions
• Generic, expressive technology to model behavior
• Overcome the Frame Problem
• Usage
• A general ASM defines the formal semantics of the
  WSMO Choreography Description Language
• Choreography Specifications are mapped into ASM
  representation to allow protocol level mediation
  operations

8
Global Model Aspects
under construction

• Definition
• a multi-participant contract that describes from
  a global viewpoint the common observable behavior
  of the collaborating WS participants
• (this is the definition of choreography from
  the W3C WS Choreography working group)
• Main Description Notions
• collaboration participants
• information interchanged
• information-driven interaction rules (channel,
  workunit,)
• this is basically what WS CDL is about

9
Mediation Aspects

• Heterogeneity
• Mismatches on structural / semantic / conceptual
  / level
• Occur between different components that shall
  interoperate
• Especially in distributed open environments
  like the Internet
• Concept of Mediation (Wiederhold, 94)
• Mediators as components that resolve mismatches
• Declarative Approach
• Semantic description of resources
• Intelligent mechanisms that resolve mismatches
  independent of content
• Mediation cannot be fully automated (integration
  decision)
• Levels of Mediation within Semantic Web Services
  (WSMF)
• Data Level mediate heterogeneous Data Sources
  
• Protocol Level mediate heterogeneous
  Communication Patterns
• Process Level mediate heterogeneous Business
  Processes

10
WSMO Mediators Structure
WSMO Mediator uses a Mediation Service via
Source Component
Target Component
1
1 .. n
Source Component

• as a Goal
• directly
• optionally incl. Mediation

under construction Semantic Mediation
Techniques for all levels
Mediation Services
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if we have all this
WS 3
C
4.
M 5
C
WS 2
1.
M 1
C
WS 1
2.
3.
M 17
C
WS n
mediated collaboration of multiple Semantic Web
Service
12
Status Outlook

• What we have so far
• WSMO supports this idea by its design
• general approach seems to be fitting
• Especially in distributed open environments
  like the Internet
• What we are currently working on
• WSMO Choreography
• General Approach
• Formal Model
• WSMO Mediators general specification
• EU-IP proposal that targets these issues
• Future Issues
• Global Models / relation to Choreography
• Mediation techniques for data, protocol, and
  business mediation level