This document provides an overview of service-oriented architecture (SOA) composition and existing solutions. It discusses key concepts like orchestration and choreography in composing services. Industry standards like UDDI, WSDL, and BPEL are described for discovering, describing, and composing services but have limitations regarding semantics. Semantic approaches like OWL-S aim to address these limitations by adding machine-readable semantics to enable automatic discovery and composition of services. Research issues in areas like quality of service, monitoring, and computing optimal compositions are also discussed. The document surveys various technologies and approaches for SOA composition.

1. Introduction
to
SOA Composition
UC San Diego
CSE 294
January 23, 2009
Barry Demchak

2. Agenda
 What is SOA Composition?
 … and what are the issues?
 Existing solutions
 UDDI/WSDL (Web Services)
 BPEL
 What’s missing?
 OWL-S
 What is OWL?
 How does OWL apply?
 Comparison of existing solutions and OWL-S
 Emerging technology choices

3. Source Material
 SOA Design Patterns: Capability Composition Patterns [in progress].
http://www.informit.com/articles/article.aspx?p=1271262
 Web Services Composition. Nikola Milanovic.
http://user.cs.tu-berlin.de/~mwerner/discourse/BlockLVS04/slides/service-composition.pdf
 SOA Source Book. The Open Group.
http://www.opengroup.org/projects/soa-book/page.tpl?CALLER=faq.tpl&ggid=1335
 Blackboard-style Service Composition with Onto<->SOA. Korotkiy & Top.
http://www.cs.vu.nl/~maksym/pap/MKorotkiy-Onto-SOA-BB.pdf
 BPEL: Service Composition for SOA. Jurac.
http://www.javaworld.com/javaworld/jw-07-2006/jw-0710-bpel.html?page=1
 SCA: Flexible and Agile Composition of Distributed SOA Applications. Edwards.
http://developers.sun.com/learning/javaoneonline/2008/pdf/TS-5850.pdf?cid=925589
 The Service Revolution - software engineering without programming languages. Alonso.
http://www.ifi.uzh.ch/ecows06/fileadmin/papers/GA-ECOWS-Nov-06.pdf
 Tools and Technologies for Semantic Web Services: An OWL-S Perspective. Sycara and
Martin. http://www.ai.sri.com/daml/services/ISWC06-OWL-S-tutorial.pdf
 Web Service Composition - Current Solutions and Open Problems. Srivastava and Koehler.
http://www.zurich.ibm.com/pdf/ebizz/icaps-ws.pdf
 Web Service Composition Standards. METEOR-S Project.
http://lsdis.cs.uga.edu/proj/meteor/mwscf/standards.html
 Tutorial on OWL. Bechhofer, Horrocks, Patel-Schneider.
http://www.cs.man.ac.uk/~horrocks/ISWC2003/Tutorial/examples.pdf
 Semantic Web Processes: Semantics Enabled Annotation, Discovery, Composition and
Orchestration of Web Scale Processes. Cardoso & Sheth.
http://lsdis.cs.uga.edu/lib/presentations/WISE2003-Tutorial.pdf
 Current Solutions for Web Service Composition. Milanovic & Malek. IEEE Internet
Computing. p51. Nov/Dec 2004.

4. The Capability Composition Pattern
A capability may not be able to
fulfill its processing requirements
without adding logic that resides
outside of its service's functional
context, thereby compromising
the integrity of its context and
risking service denormalization.
[SOA Design Patterns]

5. The Capability Composition Pattern
[SOA Design Patterns]

6. Basic Composition
 Orchestration – engine controls service via single script,
and service invokes other services in single swim lane
 Choreography – engine controls all services via scripts
associated with services; they execute in multiple swim lanes
[SOA Source Book]

7. Main Composition Approaches
 “Industry”
 UDDI / WSDL / BPEL or SCA Infrastructure
 Plumbing created by programmer (limited
scalability to large and diverse service spaces)
 Semantic Web Services
 OWL-S
 Focuses on semantic compatibility and
automatic service discovery
 Other
 Blackboard Systems

8. “Industry Solutions” – UDDI/WSDL
 UDDI: service registry
 WSDL: registry
document
 Defines location and
parameters/messages
for available services in
searchable way
[WSPS]

9. WSDL (Web Services Description Language)
 XML-based description of characteristics of a
web service [INFIT]
 Function signatures (in, out, in/out, return)
 Service binding (URL and protocol)
 Stored in repositories such as UDDI
 Used to create client-side proxies
 Enables dynamic binding for clients capable
of binding dynamically

10. WSDL Content

11. UDDI/WSDL Open Questions
 What do its parameters mean?
 In what units are its parameters expressed?
 Given meaningful inputs, what is the meaning
of the product of a service?
 What are its restrictions?
 What non-functional characteristics
distinguish one service from another?
 How can I compose 10 different services so
that they fit together and produce a
meaningful result?

12. “Industry Solutions” – BPEL4WS
 Process (BPEL composition)
 Partners (participating services)
 Activities (message exchange)
[SOA Design Patterns]

13. “Industry Solutions” – BPEL4WS
Basic Flow Elements
 <process>
 <invoke>, <invoke>…<receive>
 Send, event, request/response
 <variable>, <assign>, <copy>
 State maintenance
 <scope>, <faultHandlers>
 Fault handling
 <flow>, <sequence>
 Parallel & sequential execution
 <switch>, <while>
 Conditional evaluation
[SOA Design Patterns] [Jurac]

14. “Industry Solutions” – BPEL4WS
[SOA Design Patterns]

15. BPEL4WS Open Questions
 Focus on connections and orchestration, but
not on correctness
 Proper function “guaranteed” by diligence of
author
 Almost same set of open questions as for
UDDI/WSDL

16. Web Service Composition Standards
 BPML -Business Process Markup Language
 Abstract model and grammer
 WSCI -Web Services Choreography Interface
 XML-based WSDL augmentation
 BPEL4WS -Business Process Execution Language/ Web Services
 Specifies business processes and interaction protocols
 WSCL -Web Services Conversation Language
 Business-level conversations w/document exchange
 BPSS -Business Process Specification Schema
 Business-level conversations w/document exchange
 DAML-S
 Ontology markup language representing process and capability
semantics
[METEOR-S]

17. The Semantic Challenge
How to compose services that we know will do what we intend??
[Sycara]

18. Framing the Problem
[Cardoso]

19. Framing the Problem
 Provide the capability to assemble (“compose”) on
short notice an improvisational confederation
 Improvisational: Constituent systems not deliberately
engineered to work together in support of the objectives of the
confederation
 Short notice: Not deliberately planned months/years ahead of
the need
Interoperability: “The ability of systems, units, or forces to provide
services to and accept services from other systems, units, or
forces and to use the services so exchanged to enable them to
operate effectively together.” (definition from Joint Pub 1-02)
[Sycara]

20. The Semantic Web and OWL
 Semantic web adds machine-readable
information to each element, giving each
element a well-defined meaning useful for
discovery, automation, integration, and reuse.
[after W3C Semantic Web Activity Statement]
[W3C]

21. The Semantic Web and OWL
 W3C Standard
 Description Logic-based language that
describes ontologies
 Defines concepts and relations between them
 Defines subset generalization
 Well understood computational properties,
including decidability
 Enables semantic reasoning (Pellet and FaCT++)
 OWL-Lite, OWL-DL, and OWL
 Three objects: concepts, individuals, properties

22. OWL Sample
 Individuals with properties
 Classes that facilitate reasoning
[Tutorial on OWL]

23. Semantic Service Challenges
 Data/Information Semantics
 Basic discovery and interoperability
 Functional/Operational Semantics
 Discovery and composition
 Execution Semantics
 For verification, validation, exception handling
 QOS Semantics
 Suitability
[Cardoso]

24. OWL-S
 Ontology Web Language for Services (W3C)
 Relies on WSDL for invocation (grounding)
 Expands UDDI for discovery (mapping)
 Suited for use with SAWSDL (Semantic Annotations
for WSDL)
 Complimentary to BPEL (local choreography)

25. OWL-S Ontology of Services
[Sycara/Payne]

26. OWL-S Components
 Service Profile
 Inputs, outputs, preconditions, results
 Provenance, QOS, Security, Policy …
 Inheritance
 Service Grounding
 Builds on WSDL
 Service Model
 Initial state, inputs, and preconditions
 Result states, outputs, effects on process
 Chaining processes to create workflow

27. The Roles
 Providers
 Specify and advertise services
 Consumers
 Specify and advertise needs
 Facilitators
 Match subscriptions to advertised services
 Deal with complex semantic requirements
 Deal with multiple sources, schemas, queries

28. Composition
 Static (author-time) and Dynamic (runtime)
 Creation of mediators between services
 Design of flows to accomplish results, much
less optimal results
[Cardoso]

29. Comparison of Industry vs Semantic
Web Approaches
 BPEL relates closely to ServiceModel
 OWL-S defines preconditions and effects,
leading to better reasoning about composition
 OWL-S classes extend reasoning to
subclasses and other relationships
 BPEL describes sequencing of activities
 BPEL describes mechanisms for catching,
handling, and compensating for faults
 BPEL leverages WS-Coordination and WS-
Transaction for defining transactional
semantics
[Cardoso]

30. Research Issues (for QOS)
 Specification
 Computation
 Monitoring
 Control
[Cardoso]

31. Computing Service Compositions
[Milanovic]

32. Other Technology Choices
 Abstract Machines [SOA Design Patterns]
 π-Calculus [SOA Design Patterns]
 Blackboard-style Service Composition
[Korotkiy]
 SCA Infrastructure [SCA]

33. Modeling Services as Abstract Machines
 Extends WSDL via contracts covering
 Non-functional properties
 Preconditions, postconditions, invariants
 Expressed via Contract Definition Language
 Formal composition operators enable
predictability and determination of correctness
 Separates “how” from “what”
 Issues:

34. SCA Infrastructure
 Objectives
 Well-defined interfaces with business-level semantics
 Standardized communication protocols
 Flexible recombination of services
 Mechanisms
 Declarative component networks (using XML) injected
at runtime
 Standard communication bindings and policy
frameworks
 Language-embedded features (e.g., policy intents &
stateful interactions via WSDL and pragma extensions)
[SCA]

35. SCA Infrastructure

36. Conferences for Service Composition
 ICWS
 WISE
 WSCA
 SCC

37. Other Sources
 [WSBP] Basic Profile Version 1.1. Web Services Interoperability
Organization (WS-I). Apr 2006. http://www.ws-
i.org/Profiles/BasicProfile-1.1.html
 [INFIT] IT Web Services: A Roadmap for the Enterprise. A.
Nghiem. Prentice Hall. Oct 2002.
http://www.informit.com/articles/article.aspx?p=31076

38. Time to take a walk!
Me
Web Services