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Service Oriented Architecture. Lecture 3: SOA Reference Model OASIS 2006. What is a Reference Model. Abstract framework for understanding significant relationships among the entities of some environment. Enables the development of specific reference or concrete architectures.

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service oriented architecture

Service Oriented Architecture

Lecture 3: SOA Reference Model OASIS 2006

Master of Information System Management

what is a reference model
What is a Reference Model
  • Abstract framework for understanding significant relationships among the entities of some environment.
  • Enables the development of specific reference or concrete architectures.
  • Is a minimal set of unifying concepts, axioms and relationships within a particular problem domain.
  • The SOA Reference Model applies to software architecture and not generally to “service environments”.

Master of Information System Management

what is a reference architecture
What is a Reference Architecture?
  • Recommended patterns.
  • Explains and underpins a generic design template.
  • A reference model, on the other hand, works at a higher level of abstraction.
  • Consider a reference model for residential housing…

Master of Information System Management

residential housing example
Residential Housing Example
  • A reference model would talk about eating areas, hygiene areas and sleeping areas.
  • More than one reference architecture may address the problem of providing housing. A reference architecture may exist for space station housing and another for high density housing.

Master of Information System Management

concrete or specific architecture
Concrete or Specific Architecture
  • In residential housing we would:
  • Incorporate particular styles.
  • Describe window arrangements.
  • Assign construction materials.
  • Present blueprints.

Master of Information System Management

reference model
Reference Model

Human Housing Issues

Reference Architecture

Reference Architecture

Space Ship Housing High Rise Housing

Specific architecture

Specific architecture

One window per kitchen

Specific solution approaches

Common courtyard

Specific solution

approaches

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slide7

How the Reference Model relates to other work

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what is soa
What is SOA?
  • Service Oriented Architecture is a paradigm for organizing and utilizing distributed capabilities that may be under control of different ownership domains.
  • Not itself a solution to domain problems but rather an organizing and delivery paradigm.
  • Key concepts are visibility, interaction and effect.

Master of Information System Management

terms
Terms
  • Visibility refers to the capacity of those with needs and those with capabilities to see each other.
  • Interaction is the activity of using capability grounded in a particular execution context.
  • Capabilities are used to realize real world effects (return of information or change in state of entities).

Master of Information System Management

terms1
Terms
  • Private actions

are inherently unknowable by other

parties. Think information hiding.

  • Public actions

result in changes to the state

that is shared between those involved

in the current execution context and

possibly shared by others.

Master of Information System Management

terms2
Terms
  • The notion of Service includes:

-- The performance of work (a function)

by one for another.

-- The capability to perform work for

another.

-- The specification of the work

offered for another.

-- The offer to perform work for

another.

-- In SOA, services are the mechanisms

by which needs and capabilities are

brought together. Think marketplace.

Master of Information System Management

terms3
Terms
  • SOA is a means of organizing solutions that promotes reuse, growth and interoperability.
  • SOA is an organizing and delivery paradigm that enables one to get more value from use both of capabilities which are locally “owned” and those under the control of others.
  • The provider of the underlying capability may not be the same entity that eventually provides the service through which

the underlying capability is accessed.

  • The entity that creates, evolves and maintains the capability may be different from the entity that creates, evolves and maintains the service.

Master of Information System Management

soa differs from oop
SOA Differs from OOP
  • The Object Oriented Paradigm focuses on packaging data with

operations. The SOA Paradigm focuses on the task or business

function. It may or may not be associated with methods and

properties.

  • To use an object, you first create it. One interacts with a service where

it exists.

  • SOA places greater emphasis on clear semantics.
  • SOA, like human activity, works by delegation.
  • SOA takes ownership boundaries more seriously.
  • SOA is more closely aligned with the marketplace. An interaction is an

exchange of value and there may exist a marketplace of services.

  • The Gang of Four OOP Design Patterns don’t apply here. We don’t

talk about inheritance, aggregation, polymorphism and so on…

  • What is Martin Fowler’s first rule of distributed objects? “Don’t

distribute your objects.”

  • SOA is all about progress through regress.
  • Services are simpler things.

Master of Information System Management

soa benefits
SOA Benefits
  • Through simplification perhaps we can:
    • Facilitate the manageable growth of large-scale

enterprise systems.

    • Facilitate internet-scale provisioning and use

of services.

    • Reduce cost in organization-to-organization

interaction.

    • Increase scalability and interoperability.
    • Allow for evolution and manageability.

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goal of soa reference model
Goal of SOA Reference Model
  • Define the essence of service oriented architecture.
  • Develop a vocabulary.
  • Be independent of technological changes.

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the reference model
The Reference Model
  • Concept of service.
  • Concepts relating to dynamic aspects of service.
  • Concepts relating to meta-level aspects of services.

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the reference model1
The Reference Model

Visibility

Service Description

Execution Context

Service

Interaction

Real world

effect

Contract and

policy

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a service
A Service

-- Is a mechanism to enable access to one or more capabilities.

-- Permits access via a clear interface.

-- Is exercised consistent with constraints and policies as

specified by the service descriptions (metadata).

Service

-- A service is opaque except for :

-- Information model

-- Behavior Model

-- Information required to match needs.

-- Effects include:

-- Information returned and/or a change in shared state

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dynamics of a service
Dynamics of a Service

Service dynamics include:

-- visibility

-- interaction

-- real world effects

Visibility

Service

Interaction

Real world

effect

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visibility a prerequisite to interaction
Visibility a Prerequisite to interaction

Awareness

Willingness

Available description

and policy

Visibility

Both parties must

want to interact.

The parties must be

able to communicate

Reachability

Interaction

Preconditions to visibility are:

awareness, willingness, and reachability

Master of Information System Management

slide21

Important Interaction Concepts

Action Model

Process Model

Service Description

Behavior Model

Interaction

The Information Model describes

the structure and semantics of

messages

Information Model

Semantics

Structure

Describes how the messages are to be

interpreted - perhaps with an ontology.

Structure includes data format

and data types

Master of Information System Management

slide22

Important Interaction Concepts

Action Model

Process Model

Service Description

Behavior Model

Interaction

A behavior model is characterized by knowledge of the actions on,

responses to, and temporal dependencies between actions on the

service.

For example, when accessing a secure database, several steps

may be required for identification, authentication and authorization

prior to issuing an SQL query.

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slide23

Important Interaction Concepts

Processes may be idempotent,

long-running, transactional, etc.

Action Model

Process Model

Service Description

Behavior Model

Interaction

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slide24

Important Interaction Concepts

Characterizes the actions that

may be invoked against the service

Process Model

Action Model

Service Description

Behavior Model

Interaction

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slide25

Real World Effect

Interactions have purpose.

The purpose is often to change

the shared state of the world or to

gain information.

Shared State

Service

Interaction

Real world

effect

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concepts about services
Concepts About services

A hallmark of SOA is the large amount of associated documentation

and description.

Service Description

Execution Context

Service

Represents the information

needed in order to use the

service.

Contract and

policy

Master of Information System Management

service description
Service Description
  • Purpose is to facilitate interaction and visibility.
  • Best if represented in a machine readable standard way.
  • Information includes:
    • Reachability
    • Set of functions performed
    • Set of constraints and policies
    • Format and content of exchanged

messages

    • Expected sequence of messages

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service description1
Service Description

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policy related to a service
Policy Related to a Service

A policy represents some constraint or condition on the use,

deployment or description of an owned entity as defined by

any participant. A policy is from a participant’s viewpoint.

A contract represents an agreement by two or more parties.

Contracts may also address condition of use issues.

Service policies involve:

Assertions - e.g. all messages will be encrypted

Ownership - e.g. the service or consumer

Enforcement - if it’s not enforced it’s a wish

Policy applies to:

Security, privacy, manageability, quality of service as well as

hours of business, return policies and so on…

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policies and contracts
Policies and Contracts

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execution context
Execution Context

The execution context of a service interaction is the set

of infrastructure elements, process entities, policy assertions

and agreements that are identified as part of an instantiated

service interaction, and thus forms a path between those with

needs and those with capabilities.

It concerns the totality of the interaction.

Different instance of the same service have different execution

contexts.

The context may evolve during a service interaction. It may

be decided, for example, that subsequent exchanges will

be encrypted.

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execution context1
Execution Context

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conformance guidelines 1
Conformance Guidelines(1)
  • Have entities that can be identified as services defined by the Reference Model.
  • Be able to identify how visibility is established between service providers and consumers.
  • Be able to identify how interactions are mediated.
  • Be able to identify how the effect of using services is understood.

Master of Information System Management

conformance guidelines 2
Conformance Guidelines (2)
  • Have descriptions associated with services.
  • Be able to identify the execution context required to support interaction.
  • It will be possible to identify how policies are handled and how contracts are modeled and enforced.

Master of Information System Management