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Service Oriented ArchitectureReference Model

An informal SOA Ontology

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Reference Model

• An abstract framework for understanding significant relationships among the entities of some environment.

• Consists of a minimal set of unifying concepts, axioms and relationships within a particular problem domain.

• Is independent of specific standards, technologies, implementations, or other concrete details.

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Reference Model

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Service Oriented Architecture

• Service Oriented Architecture is a paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains.

• Goal of this reference model is to define the essence of Service Oriented Architecture

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Why Service Oriented Architecture?

• Drivers:• Large scale Enterprise systems• Internet scale provisioning of services• Reduce the cost of doing business

• Benefits• Build scalable, evolvable systems

• Scalable because minimizes assumptions

• Manage complex systems• Encourage re-use of business function

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Why is it different?

• SOA reflects the reality of ownership boundaries• CORBA, RMI, COM, DCOM, etc. all try to

implement transparent distributed systems• Ownership is of the essence in SOA

• SOA is task oriented• Services are organized by function

• Getting something done

• SOA is inspired by human organizations• It worked for us, it should work for machines

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What is not in the RM

• Service composition• Choreography, orchestration• Process Oriented Architecture

• Organizational framework• Who is doing what to whom

• Specific technologies• not even specific architectures

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Key concepts

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Service

• A mechanism to enable access to one or more capabilities• using a prescribed interface • consistent with constraints and

policies as specified by the service description.

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Visibility

• Awareness• Service description

• Discovery

• Willingness• Policy & contract

• Reachability• Communication

Visibility is the relationship between service participants that is satisfied when they are able to interact with each other

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InteractionInteracting with a service involves performing actions against the service

The extent to which one system can effectively interpret information from another system is governed by thesemantic engagement of the various systems.The semantic engagement of a system is a relationship between the system and information it may encounter.

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Real World EffectThe purpose of using a capability is to realize one or more real world effects. At its core, an interaction is “an act” as opposed to “an object” and theresult of an interaction is an effect (or a set/series of effects).

The real world effect is couchedin terms of changes to the state shared bythe participants and stakeholders ina service interaction

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About Services

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Conditions and Expectations

• Policy• Constraint representing the

intention of a participant in a service

• Contract• Constraint representing an

agreement between two or more participants.

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DescriptionThe service description represents the informationneeded in order to use, manage or provide a service.

• Service reachability• Service Functionality• Service Policies• Service Interface

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Execution ContextThe execution context is the set of infrastructure elements,process entities, policy assertions and agreements that areidentified as part of an instantiated service interaction,and thus forms a path between those with needs and thosewith capabilities

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Is a Reference Model an Ontology?

• Establishing a vocabulary• A lot of definitions

• The RM glossary has 28 entries

• Formality was considered• Audience is not formal• Mechanical processing of RM not expected

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What about UML

• UML obvious choice for an architecture spec

• But,• Inheritance (is-a) relationship almost never

used• Extraneous precision

• E.g. we tried to define Service, not count the number of service providers

• It’s so ugly <duck/>

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An early concept map

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Concepts MapsConcepts maps were excellent graphical indices to text

Concepts, and relationships. All we needed

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On the cutting-room floor…

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Where we are

• Committee Specification published

• Reference Architecture effort started

http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=soa-rm