Survey of Dynamic Web Service Composition Techniques

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Survey of Dynamic Web Service Composition
Techniques
Presented By Atif Alamri (atif_at_mcrlab.uottawa.ca
) Mohamad Eid (eid_at_mcrlab.uottawa.ca )

• ELG 5121
• Multimedia Communications
• Prof. Abdulmotaleb El Saddik
• Nov. 1, 2005

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Outline

• Introduction
• Web services architecture
• Advantages of web services
• Service composition
• Elementary vs. composite services
• Drivers for composition
• Dynamic service composition
• Static vs. dynamic and Manual vs. automatic
• Beneficial aspects of dynamic web service
  composition
• Challenges in dynamic web service composition
• Classification of Composition techniques
• Runtime reconfiguration using wrappers
• Runtime component adaptation
• Composition language
• Workflow driven composition techniques
• Ontology driven web service composition
  techniques

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Web services architecture

• A web service is a self-contained, language
  neutral, platform independent, and loosely
  coupled application
• It can be described, published, located, and
  invoked over the Internet

SOAP Interpreter
SOAP Interpreter
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Advantages of web services

• Loose Coupling
• Standard-Based (interoperability)
• Flexibility
• Reusability
• Scalability
• Reduced Complexity
• Programmatically Accessible
• Application-to-Application Communication

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The need for web service composition

• Composition is the ability to provide value-added
  services through integration of other web service
  components
• Services are classified as elementary and
  composite
• Drivers for Composition
• Managing Increased Complexity
• Engine-Oriented Software Applications
• Cross-Domain Services
• Bridging Network Protocols

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Dynamic service composition

• Manual vs. automatic
• Manual composition is performed by means of
  employees who have access to the elementary
  services
• Automatic implies that a software agent performs
  composition based on some predefined algorithm
• Static vs. Dynamic
• Static composition is performed at design or
  compile time
• Dynamic composition is performed at execution
  time
• We will focus on Dynamic web service Composition

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Why dynamic web service composition

• Greater Flexibility
• The customization of software based on
  individual needs of a user can be made dynamic
• New Services can be created at runtime
• The capabilities of the application can be
  extended at runtime
• Users are not interrupted during upgrades of
  applications
• Users can continue to interact with the old
  services while composition of new services is
  taking place
• Unlimited Set of Services
• unlimited number of new services can be created
  from limited set of service components

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Challenges in dynamic composition

• The dynamic procedures are very complicated
• Composition is useful to provide runtime
  specified services
• Dynamic Composition has limited applicability to
  everyday software systems
• Dynamic composition is the only means to change
  the behavior of running applications
• Upgrading Software may be more difficult
• New versions of components can be introduced,
  thus making upgrading possible
• It is much slower than static composition
• Not necessarily true
• Significant Infrastructure is required to support
  dynamic composition
• The extra requirement is a component model that
  supports dynamic binding and runtime
  extensibility of components

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Composition techniques 1/6 Runtime
reconfiguration using wrappers

• A wrapper is used to provide the additional
  context dependency interfaces to the component so
  that it can interact with a new component

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Composition techniques 1/6 Runtime
reconfiguration using wrappers

• Pros
• Extending the implementation of components
  without changing the code
• Provide additional context interfaces to interact
  with new components
• Adapting running components to new behaviors
  (facilitates unanticipated, dynamic component
  adaptation)
• Doesnt need knowledge of internals of services
  (only interfaces)
• Cons
• Recursive composition is complicated
• Unnecessary methods or interfaces may exist
• Doesnt support unanticipated runtime
  reconfiguration
• Type conflict may occur between existing
  component and newly introduced component

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Composition techniques 2/6 Runtime component
adaptation

• Adapting components into new components or
  services by changing the interfaces and/or
  behavior of the component at runtime

Component
onOutgoingMessage()
Layer message handler
onOutgoingMessage()
Adapter
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Composition techniques 2/6 Runtime component
adaptation

• Pros
• Make potentially incompatible components into
  composable components
• New atomic service is produced that can be
  advertised
• Impose predefined but configurable types of
  functionalities
• New atomic service is produced that can be
  advertised.
• Type safe and dynamic delegation is possible
• Cons
• Require tempering of the service code.
• Doesnt support distributed execution.
• Complex monitoring and recovery mechanisms.
• Names of some interfaces dont match expected
  names of methods
• Dont define restricted client access to specific
  interfaces.
• Class replacement is very difficult in a running
  system

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Composition techniques 3/6 Composition Language

• A combination of architectural description
  language (ADL), a scripting language, a glue
  language, and a coordination language
• Pros
• Specifically designed to assemble components
• Uses components that have standardized interfaces
• Define higher level abstraction to better
  describe composition
• Cons
• More complex in comparing with other techniques
• Recursive composition is not possible
• Components must be designed to be composed or
  they will not be composable interfaces

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Composition techniques 4/6 Workflow Driven
Composition

• Builds web services to an abstract process based
  on business and process constraints and generate
  an executable process

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Composition techniques 4/6 Workflow Driven
Composition

• Pros
• Users can participate in composition
• Simple monitoring and recovery procedures
• Recovery plans can be included in the workflow
• Easier to impose distributed execution of
  composite services
• Cons
• Composed service cant be advertised
• Recursive composition becomes more difficult
• Unavailability of any service causes failure of
  execution of the composite service

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Composition techniques 5/6 Ontology Driven
Composition

• The ontological descriptions and relationships of
  web services with other services are used to
  automatically and semi-automatically composing
  web services

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Composition techniques 5/6 Ontology Driven
Composition

• Pros
• Consider semantics
• Supports easier forms of requesting composition
  (English-like queries)
• Can be integrated with any other technique
• Enables distributed composition and execution
• Cons
• Too hard to verify the effectiveness of the
  ontology
• Domain specific
• No agreed-upon taxonomy as the foundation of the
  ontology
• Assumes that elementary services are semantically
  represented
• Complex monitoring and recovery mechanisms
• Failure prone

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Composition techniques 6/6 Declarative
Composition

• Using composability rules to determine whether
  two services are composable
• Pros
• Mathematically approved
• Can reach optimality
• Doesnt need knowledge of the internal
  implementation of services
• Allow distributed composition and execution
• Cons
• Uses direct matching
• Constraints based
• Uses rules which increase its complexity
• Class replacement is impossible in a running
  system

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Dynamic Composition Techniques Summary
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General Requirements for Dynamic Composition

• Query Parser
• Decomposes user query into a set of requirements
• Service Selection Module
• Decomposes user requirements into an abstract
  service and specify the proper services.
• Composition Engine
• Uses one of dynamic composition techniques to
  answer the how question of composition
• Verification Module
• To verify that the composite service satisfy the
  users query
• QoS Certifier
• Checks for functional and/or nonfunctional QoS
  parameters

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General Requirements for Dynamic Composition

• Execution Engine
• Executes the composite service by invoking
  individual components and matching interfaces
• Monitoring and Recovery Module
• Showing the status of the component services and
  handling exceptional states
• Controllability Agent
• Provides controllability on composition,
  execution, and recovery processes
• Composite Service Description and Advertisement
• To describe and advertise the composite service
  to support recursive composition

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Trends in Dynamic Composition Techniques

• Distributed execution of composite services
• Ontology development to facilitate semantic
  composition
• Integration of different techniques to improve
  overall performance

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Selected References

• Dustdar, S. and Schreiner, W. (2005) A survey on
  web services composition, Int. J. Web and Grid
  Services, Vol. 1, No. 1, pp.130.
• Jinghai Rao and Xiaomeng Su, A Survey of
  Automated Web Service Composition Methods, In
  Proceedings of the First International Workshop
  on Semantic Web Services and Web Process
  Composition, SWSWPC 2004, San Diego, California,
  USA, July 6th, 2004, Springer-Verlag.
• K. Fujii and T. Suda, Dynamic Service
  Composition Using Semantic Information,
  ICSOC04, November 15--19, 2004, New York, USA.
• José Luis Ambite, Genevieve Giuliano, Peter
  Gordon, Qisheng Pan, Naqeeb Abbasi, LanLan Wang,
  Matthew Weathers, Argos dynamic composition of
  web services for goods movement analysis and
  planning, Proceedings of the 2005 national
  conference on Digital government research
  dg.o2005, May 2005.
• José Luis Ambite, Matthew Weathers, Automatic
  composition of aggregation workflows for
  transportation modeling, Proceedings of the 2005
  national conference on Digital government
  research dg.o2005, May 2005.
• B. Benatallah, M. Dumas, Q. Sheng, and A. Ngu.
  Declarative composition and peer-to-peer
  provisioning of dynamic web services, In
  Proceedings of the International Conference on
  Data Engineering (ICDE), 2002.

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• THANK YOU
• Questions ?
• We are willing to answer Off-line questions on
  atif_at_mcrlab.uottawa.ca and eid_at_mcrlab.uottawa.ca