Service-centric Software Engineering Objectives Topics covered Service-oriented architectures Service-oriented architectures

Service-centric Software Engineering Objectives Topics covered Service-oriented architectures Service-oriented architectures www.phwiki.com

Service-centric Software Engineering Objectives Topics covered Service-oriented architectures Service-oriented architectures

Bierley, Angie, Morning Executive Producer has reference to this Academic Journal, PHwiki organized this Journal Service-centric Software Engineering Objectives To explain the notion of a reusable service, based on web service st in addition to ards, that provides a mechanism as long as inter-organisational computing; To describe the service engineering process that is intended to produce reusable web services; To introduce service composition as a means of application development; To show how business process models may be used as a basis as long as the design of service-oriented systems. Topics covered Services as reusable components Service engineering Software development with services

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Service-oriented architectures A means of developing distributed systems where the components are st in addition to -alone services Services may execute on different computers from different service providers St in addition to ard protocols have been developed to support service communication in addition to in as long as mation exchange Service-oriented architectures Benefits of SOA Services can be provided locally or outsourced to external providers Services are language-independent Investment in legacy systems can be preserved Inter-organisational computing is facilitated through simplified in as long as mation exchange

Web service st in addition to ards Key st in addition to ards SOAP A message exchange st in addition to ard that supports service communication WSDL (Web Service Definition Language) This st in addition to ard allows a service interface in addition to its bindings to be defined UDDI Defines the components of a service specification that may be used to discover the existence of a service WS-BPEL A st in addition to ard as long as workflow languages used to define service composition Service-oriented software engineering Existing approaches to software engineering have to evolve to reflect the service-oriented approach to software development Service engineering. The development of dependable, reusable services Software development as long as reuse Software development with services. The development of dependable software where services are the fundamental components Software development with reuse

Services as reusable components A service can be defined as: A loosely-coupled, reusable software component that encapsulates discrete functionality which may be distributed in addition to programmatically accessed. A web service is a service that is accessed using st in addition to ard Internet in addition to XML-based protocols A critical distinction between a service in addition to a component as defined in CBSE is that services are independent Services do not have a ‘requires’ interface Services rely on message-based communication with messages expressed in XML Synchronous interaction An order as an XML message

Web service description language The service interface is defined in a service description expressed in WSDL. The WSDL specification defines What operations the service supports in addition to the as long as mat of the messages that are sent in addition to received by the service How the service is accessed – that is, the binding maps the abstract interface ontoa concrete set of protocols Where the service is located. This is usually expressed as a URI (Universal Resource Identifier) Structure of a WSDL specification A WSDL description fragment

A WSDL description fragment 2 Service engineering The process of developing services as long as reuse in service-oriented applications The service has to be designed as a reusable abstraction that can be used in different systems Involves Service c in addition to idate identification Service design Service implementation The service engineering process

Service c in addition to idate identification Three fundamental types of service Utility services that implement general functionality used by different business processes Business services that are associated with a specific business function e.g., in a university, student registration Coordination services that support composite processes such as ordering Service classification Service identification Is the service associated with a single logical entity used in different business processes Is the task one that is carried out by different people in the organisation Is the service independent Does the service have to maintain state Is a database required Could the service be used by clients outside the organisation Are different users of the service likely to have different non-functional requirements

Catalogue services Created by a supplier to show which good can be ordered from them by other companies Service requirements Specific version of catalogue should be created as long as each client Catalogue shall be downloadable The specification in addition to prices of up to 6 items may be compared Browsing in addition to searching facilities shall be provided A function shall be provided that allows the delivery date as long as ordered items to be predicted Virtual orders shall be supported which reserve the goods as long as 48 hours to allow a company order to be placed Catalogue – Non-functional requirements Access shall be restricted to employees of accredited organisations Prices in addition to configurations offered to each organisation shall be confidential The catalogue shall be available from 0700 to 1100 The catalogue shall be able to process up to 10 requests per second Catalogue service operations

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Service interface design Involves thinking about the operations associated with the service in addition to the messages exchanged The number of messages exchanged to complete a service request should normally be minimised. Service state in as long as mation may have to be included in messages Interface design stages Logical interface design Starts with the service requirements in addition to defines the operation names in addition to parameters associated with the service. Exceptions should also be defined Message design Design the structure in addition to organisation of the input in addition to output messages. Notations such as the UML are a more abstract representation than XML WSDL description The logical specification is converted to a WSDL description Catalogue interface design

Input in addition to output message structure Service implementation in addition to deployment Programming services using a st in addition to ard programming language or a workflow language Services then have to be tested by creating input messages in addition to checking that the output messages produced are as expected Deployment involves publicising the service using UDDI in addition to installing it on a web server. Current servers provide support as long as service installation A UDDI description Details of the business providing the service An in as long as mal description of the functionality provided by the service In as long as mation where to find the service’s WSDL specification Subscription in as long as mation that allows users to register as long as service updates

Service testing problems External services may be modified by the service provider thus invalidating tests which have been completed Dynamic binding means that the service used in an application may vary – the application tests are not, there as long as e, reliable The non-functional behaviour of the service is unpredictable because it depends on load If services have to be paid as long as as used, testing a service may be expensive It may be difficult to invoke compensating actions in external services as these may rely on the failure of other services which cannot be simulated Key points Service-oriented software engineering is based on the notion that programs can be constructed by composing independent services which encapsulate reusable functionality. Service interfaces are defined in WSDL. A WSDL specification includes a definition of the interface types in addition to operations, the binding protocol used by the service in addition to the service location. Services may be classified as utility services, business services or coordination services. The service engineering process involves identifying c in addition to idate services as long as implementation, defining the service interface in addition to implementing, testing in addition to deploying the service. Key points Service interfaces may be defined as long as legacy software systems which may then be reused in other applications. Software development using services involves creating programs by composing in addition to configuring services to create new composite services. Business process models define the activities in addition to in as long as mation exchange in business processes. Activities in the business process may be implemented by services so the business process model represents a service composition. Techniques of software testing based on source-code analysis cannot be used in service-oriented systems that rely on externally provided services.

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