1 V8: Service-based Interoperability – 1 Dr.-Ing. Reiner Wichert Fraunhofer-Institut für...

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V8: Service-based Interoperability – 1

Dr.-Ing. Reiner WichertFraunhofer-Institut für Graphische Datenverarbeitung IGD

Holger Graf

Fraunhofer-Institut für Graphische Datenverarbeitung IGD

Mohammad-Reza (Saied) Tazari

Fraunhofer-Institut für Graphische Datenverarbeitung IGD

Ambient IntelligenceWS 10/11

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Gliederung

OASIS SOA Referenzmodell & Referenzarchitektur

▫ Definition Service-orientierte Architekturen

▫ Wichtige Begriffe aus dem Referenzmodell

▫ Beispielmodelle aus der Referenzarchitektur

Bespiel einer SOA: Web Services

Nächste Woche: Die OWL-S Ontologie für Dienstebeschreibung

Nächste Woche: Service Management in PERSONA

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Literatur

Spezifikationen der technischen Komitee für SOA

Referenzmodell bei der OASIS (Organization for the Advancement of

Structured Information Standards www.oasis-open.org):

SOA Referenzmodell

http://docs.oasis-open.org/soa-rm/v1.0/soa-rm.pdf

SOA Referenzarchitektur

http://docs.oasis-open.org/soa-rm/soa-ra/v1.0/soa-ra-cd-02.pdf

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Reference Model

• A reference model

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

enables the development of specific reference or concrete architectures and consistent standards or specifications.

consists of a minimal set of unifying concepts, axioms and relationships within a particular problem domain,

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

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Reference Model vs. Reference Architecture

• A reference architecture

architectural design pattern showing what is involved in realizing the

entities identified in an underlying reference model

indicates how an abstract set of mechanisms and relationships realizes a

predetermined set of requirements

models the abstract architectural elements (building blocks) in the

domain independent of the technologies, protocols, and products that are

used to implement the domain

• One or more reference architectures may be derived from a

common reference model,

to address different purposes/usages to which the reference model may be

targeted.

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Zusammenhang zwischen Referenzmodell und Referenzarchitekturam Beispiel von SOA

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Service-orientierte Architekturen (SOA)

• SOA ist ein Paradigma für die Bereitstellung und Inanspruchnahme

verteilter Kompetenzen, die möglicherweise unter der Kontrolle

verschiedener Eigentümerschaftsdomänen stehen

• Entitäten (Menschen und Organisationen) erzeugen Kompetenzen

Probleme Lösen oder Lösungsfindung unterstützen

geschäftsbetrieben

▫ Bedürfnisse werden durch von einem Anderen angebotenen Kompetenzen

befriedigt

oder, in der Welt verteilten Computings werden Anforderungen einer

Komponente von einer Komponente mit einem anderen Besitzer erfüllt

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• Keine Garantie für eine eins-zu-eins Korrelation zwischen Bedürfnissen

und Kompetenzen

jede Seite, von elementar bis Komplex

einer Nachfrage kann manschmal nur mit einer Kombination von

Angeboten nachgekommen werden

ein Angebot kann mehrere Bedürfnisse abdecken

• SOA bietet ein mächtiges Rahmenwerk für Abbildung von

Bedürfnissen auf Kompetenzen, mit der Möglichkeit Angebote für die

Befriedigung von Nachfragen zu kombinieren

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• SOA unterstützt Wiederverwendung, Zuwachs und Interoperabilität

• keine Lösung für Domänenprobleme

Paradigma für Bereitstellung und Lieferung

Mehrwert durch Ausnutzung eigener und fremder

Kompetenzen

• einfacher, eine identifizierte Lösung zu modifizieren oder alternative

Lösungen anzustreben

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Gliederung








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SOA Referenzmodell: Hauptbegriffe

ServiceDescription

ExecutionContext

Real WorldEffect

Interaction

Visibility

Service

Contract &Policy

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• A service is a mechanism to enable access to one or more capabilities.

• The access is provided using a prescribed interface and is exercised consistent with constraints and policies as specified by the service description.

• A service is provided by an entity – the service provider – for use by others; the eventual consumers of the service

may not be known to the service provider and

may demonstrate uses of the service beyond the scope originally conceived by the provider

OASIS Definition für Service – 1

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• A service is accessed by means of a service interface.

• The interface comprises the specifics of how to access the underlying capabilities.

• There are no constraints on what constitutes the underlying capability or how access is implemented by the service provider.

• Thus, the service could carry out its described functionality through one or more automated and/or manual processes that themselves could invoke other available services.


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• A service is opaque in that its implementation is typically hidden from the service consumer, except for:

1. the information and behavior models exposed through the service interface and

2. the information required by service consumers to determine whether a given service is appropriate for their needs.

• Important: distinction between a capability that represents some functionality created to address a need and the point of access where that capability is brought to bear in the context of SOA

may not be critical (i.e. the service may be talked about in terms of being the capability)


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• The consequence of invoking a service is a realization of one or more real world effects. These effects may include:

1. information returned in response to a request for that information,

2. a change to the shared state of defined entities,

3. or some combination of (1) and (2).

• Note, the service consumer

in (1) does not typically know how the information is generated, e.g. whether it is extracted from a database or generated dynamically;

in (2), it does not typically know how the state change is effected.


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Definition für Service von Tazari et al – 1

Service: Embodiment of a specific value addressing a need provided by one

party (service provider) to another (service consumer). As a result of consuming

a service, the consumer perceives value such as being relieved of a certain task.

In the process of providing a service, several (hardware / software / human)

resources might be involved; in particular, other subordinate services might be

utilized, as well.

Service Component: A software component, e.g. a Web Service or a plain old

Java object, which provides a set of service utilities in the virtual realm.

Service Utility: A utility in virtual realm, such as an exported method of an object

or an exported operation of a Web Service, which makes it possible to utilize a

service from within the virtual realm. A service utility may directly trigger the

process of providing the underlying service or just lead to an arrangement for

starting the process at a later point in time.

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Definition für Service von Tazari et al – 2

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• From a dynamic perspective, there are three fundamental concepts

that are important in understanding what is involved in interacting

with services:

the visibility between

service providers

and consumers,

the interaction between them,

and the real world

effect of interacting

with a service.

Real WorldEffect

Interaction

Visibility

Service

Concepts around the dynamics of service

Key Concepts of SOA – Dynamics of Services

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• For a service provider and consumer to interact with each other

they have to be able to ‘see’ each other.

• This is true for any consumer/provider relationship – including in an

application program where one program calls another:

without the proper libraries being present

the function call cannot complete.

• However, it should be emphasized that for visibility in SOA

it is not necessarily obvious how service participants

can see each other.

Key Concepts of SOA – Visibility (1)

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it is not necessarily

obvious how

Service participants

can see each other.

OASIS Definition: Visibility

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• This is typically done by providing descriptions for such aspects as:

Functions

Technical requirements

Related constraints

Related policies

Mechanisms for access or response.

• The descriptions need to be in a form (or can be transformed to a form) in which their syntax and semantics are widely accessible and understandable.

Key Concepts of SOA – Visibility (3)

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Service Interaction

Concepts

Key Concepts of SOA – Interaction

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• visibility introduces the possibilities for matching needs to capabilities (and vice versa),

interaction is the activity of using a capability.

• interaction proceeds mediated by the exchange of messages

through a series of information exchanges and invoked actions.

• many facets of interaction, all grounded in a particular…

execution context – the set of technical and business elements that form a path between those with needs and those with capabilities, which

▫ permits service providers and consumers to interact, and

▫ provides a decision point for any policies and contracts that may be in force.

Key Concepts of SOA – Interacting with Services (1)

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• Interacting with a service involves performing actions against the

service.

• In many cases, this is accomplished by sending and receiving

messages.

• other modes possible that do not involve explicit message

transmission. E.g. a service interaction effected by modifying the

state of a shared resource.

• for simplicity - message exchange as the primary mode of

interaction with a service.

Key Concepts of SOA – Interacting with Services (2)

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Principal concepts in the Reference Model

ServiceDescription

ExecutionContext

Real WorldEffect

Interaction

Visibility

Service

Contract &Policy

Key Concepts of SOA – Real world Effect

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• There is always a particular purpose associated with interacting with a service.

• Conversely, a service provider (and consumer) often has a-priori conditions that apply to its interactions. The service consumer is trying to achieve some result by using the service, as is the service provider.

• On consumer side, such a goal can often be expressed as “trying to get the service to do something” - the “real world effect” of using a service.

Example: an airline reservation service can be used to learn about available flights, seating and ultimately to book travel – the desired real world effect being information and a seat on the right flight.

Key Concepts of SOA – Real world Effect (1)

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• The purpose of using a capability is to realize one or more real

world effects.

• The expected real world effects form an important part of the

decision on whether a particular capability matches similarly

described needs.

• At the interaction stage, the description of real world effects

establishes the expectations of those using the capability.

• Note, it is not possible to describe every effect from using a

capability.

A cornerstone of SOA is that capabilities can be used without needing to

know all the details.

Key Concepts of SOA – Real world Effect (2)

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Key Concepts of SOA – Service Description

• Visibility is promoted through the service description, which

contains the information necessary to interact with the service

and describes this in such terms as the service inputs, outputs,

and associated semantics.

• The service description also conveys what is accomplished when

the service is invoked and the conditions for using the service.

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SOA and Web Services

• Although SOA is commonly assumed to be about Web Services,

services can be made visible, support interaction, and generate

effects through other implementation strategies. OSGi framework

provides such an alternative implementation strategy.

• Web service-based architectures and technologies are specific

and concrete.

• While the concepts in the SOA Reference Model apply to such

systems, Web Services are too solution-specific to be part of a

general reference model.

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Gliederung








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SOA Referenzarchitektur

• Instead of visualizing a SOA as a single complex machine, OASIS

Reference Architecture Foundation views it as an ecosystem: a space

people, machines and services inhabit in order to further both their own

objectives and the objectives of the larger community

• model the system as a network of peer-like entities instead of specifying an

application hierarchy

• specify rules for the interactions between participants instead of specifying

a hierarchy of control

• SOA ecosystem principles

• medium for exchange of value between independently acting participants

• that have legitimate claims to ownership of resources made available

• based on a series of policies and contracts capturing rules of engagement

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OASIS Architektursichten – 1

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OASIS Architektursichten – 2

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SOA Realization View: Example of Service Description

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SOA Realization View: Example of Mediated Service Awareness

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Gliederung








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Introduction: Web Services

Referenz: http://www.w3.org/TR/ws-arch/

What is a Web Service?

A software system designed to support interoperable machine-to-machine interaction over a network.

It has an interface described in a machine-processable format (specifically WSDL).

Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.

A Web service is an abstract notion that must be implemented by a concrete agent.

▫ The agent is the concrete piece of software or hardware that sends and receives messages, while the service is the resource characterized by the abstract set of functionality that is provided.

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The General Process of Engaging a Web Service

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Meta Model of the Architecture

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Simplified Message Oriented Model

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Message Oriented Model

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Simplified Service Oriented Model

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Service Oriented Model

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Simplified Resource Oriented Model

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Resource Oriented Model

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Simplified Policy Model

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Policy Model

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Web Services Architecture Stack

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http://www.w3.org/TR/soap12-part1/

http://www.w3.org/TR/soap12-part2/

Web Services communication protocol

XML extension

A convention for doing Remote Procedure Calls (RPC):

▫ Request (SOAP message)

▫ Response (SOAP message)

Current Status:

▫ Developed by Microsoft, DevelopMentor, UserLand, Lotus and

IBM

SOAP - Simple Object Access Protocol

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http://www.w3.org/TR/wsdl20/

http://www.w3.org/TR/wsdl20-adjuncts/

Structured mechanism to describe:

▫ Abstract operations that a Web Service can perform

▫ Format of messages it can process

▫ Protocols it can support

Physical bindings to:

▫ communication languages, e.g. SOAP or HTTP messages

▫ Location of services, i.e. URI and port numbers

▫ XML based

WSDL - Web Services Description Language

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WSDL - Web Services Description Language

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Discovery Process

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http://www.oasis-open.org/committees/uddi-spec

Public directory for registering and looking up services

A directory entry has three main parts:

▫ White pages: to describe the company offering the service

▫ Yellow pages: to categorize services by industry type (e.g. SIC)

▫ Green pages: to describe the interface to a web service

Uses Type Model or Model documents

Current Status:

▫ Industry initiative in OASIS led by Microsoft, IBM and Ariba;

more than 300 companies participating

UDDI - Universal Discovery, Description & Integration

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Web Services - Limitations

What is the problem?

automated localization of web services in the internet

Semantic Descriptions Needed

Why is that a problem?

Technologies used to support the application of Web Services are not sufficient: UDDI, WSDL

Current state: manual search for Web Services

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Danke für die Aufmerksamkeit

&

bis zur nächsten Vorlesung

1 V8: Service-based Interoperability – 1 Dr.-Ing. Reiner Wichert Fraunhofer-Institut für...

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