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Service Oriented Architecture
The document discusses Service-Oriented Architecture (SOA), outlining the evolution of system architecture from monolithic to n-tier structures, and defining services as reusable components that facilitate communication and integration between software systems. It covers key concepts such as service engineering, WSDL standards, the benefits of SOA, and the process of developing reusable services through identification, design, implementation, and testing. The document also highlights the importance of service interfaces for legacy systems and service composition to create new applications.
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Service Oriented Architecture
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- 2. Agenda • Introduction toservice oriented architecture • Services as reusable components • Service engineering Service candidate identification Service design Service implementation and deployment • Software development with services • Key points • References
- 3. Introduction to SOA Evolutionof System Architecture The system layers • Presentation Layer • Business Logic Layer • Data Access Layer
- 4. Introduction to SOA Evolutionof System Architecture(con. ) 1-Tier Architecture Presentation, business logic, and data access are intertwined in one monolithic mainframe application.
- 5. Introduction to SOA Evolutionof System Architecture(con. ) 2-Tier Architecture Separation of front end from other 2 layers • Client/server systems with thin clients/fat clients • Use RPC (Remote Procedure Calls) to communicate between tiers
- 6. Introduction to SOA Evolutionof System Architecture(con. ) 3-Tier Architecture Separating data access layer from Business logic (middleware)
- 7. Introduction to SOA Evolutionof System Architecture(con. ) N-Tier Architecture N-tier is a generalisation of the 3-tier architecture. • Most 3-tier systems connect into other systems in order to complete the processing.
- 8. Introduction to SOA getProduct() AppServer A App Server B getProductCall () DB (A) .jar getProduct() v2 DB (B)
- 9. Introduction to SOA Definitionof service Service Consumer Service Provider Service request Service response S e r v i c e Software Software
- 10. Introduction to SOA Definitionof service • A service is a unit of work done by a service provider to achieve desired end results for a service consumer. Both provider and consumer are roles played by software agents on behalf of their owners. • Service is a well defined function that does not depend on the state of other services.
- 11. Introduction to SOA Definitionof SOA • A Service-Oriented Architecture (SOA) is a system consisting of software components with standardized component-access and usage interfaces that are independent of any specific platform or implementation technology. • SOA is a solution for making two software to communicate to each other. • SOAs are a way of developing distributed systems where the system components are stand-alone services, executing on geographically distributed computers.
- 12. Introduction to SOA Service-OrientedArchitecture
- 13. Introduction to SOA WebService Standards
- 14. Introduction to SOA KeyStandards • SOAP A message exchange standard that supports service communication • WSDL (Web Service Definition Language) This standard allows a service interface and its bindings to be defined • WS-BPEL (Web service Business Process Execution Language) A standard for workflow languages used to define service composition
- 15. Introduction to SOA Aservice-based, in-car information system
- 16. Introduction to SOA Benefitsof 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 information exchange
- 17. Services as Reusable Components • Servicesare independent • Existing services can more easily be reuse because services in a standard way. • Software systems can be constructed by composing other services. • Encapsulates functionality (provides interface that allows access to the service functionality). 17
- 18. Services as Reusable Components • Encapsulatesfunctionality (provides interface that allows access to the service functionality). • Services are platform and implementation- language independent. In practice, a service is implemented by Microsoft’s .NET Framework 18
- 19. Web Service Description Language The serviceinterface is defined in a service description expressed inWSDL (Web Service Description Language). TheWSDL specification defines 3 parts ofWS: What operations the service supports and the format of the messages How the service is accessed - specifies communication by exchanging messages, expressed in XML using protocols such as HTTP andTCP/IP Where the service is located.This is usually expressed as a URI (Universal Resource Identifier) 19
- 20. Organization of A WSDL Specification Service-oriented architecture20 WSDL specifications are now rarely written by hand and most of the information in a specification can be automatically generated.
- 21. Part of aWSDL description for a web service 21 Major problem does not include any information about non function requirements (performance , dependability) discovered by experiments !!
- 22. Comparison between SOAP/WSDL And RESTfull 22 SOAP/WSDL RESTFULL Services describedusing WSDL and accessed via SOAP (is a message interchange standard that supports the communication between services ) Approach supports efficient service communication By URL communicates using methods GET, PUT, POST, and DELETE WS-Reliability Messaging : ensures messages will be delivered once and once only. WS-Transactions : defines how transactions across distributed services should be coordinated. it does not support enterprise-level features such as WS-Reliability and WS-Transactions. involve a lower overhead than big data services much simpler method than SOAP/WSDL for implementing web services
- 23. Service Engineering The processof developing services for reuse in service- oriented applications The service has to be designed as a reusable abstraction that can be used in different systems. Generally useful functionality associated with that abstraction must be designed and the service must be robust and reliable. The service must be documented so that it can be discovered and understood by potential users. 23
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- 25. Stages of Service Engineering Service candidateidentification where you identify possible services that might be implemented and define the service requirements. Service design where you design the logical andWSDL service interfaces. Service implementation and deployment where you implement and test the service and make it available for use. 25
- 26. Servicecandidate identification Service candidateidentification involves understanding an organization’s business processes to decide which reusable services could support these processes.
- 27. Service candidate identification Three fundamentaltypes 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. 27
- 28. Service identification Is theservice 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? 28
- 29. Service Identification Example A largecompany, which sells computer equipment, has arranged special prices for approved configurations for some customers. To facilitate automated ordering, the company wishes to produce a catalog service that will allow customers to select the equipment that they need. Unlike a consumer catalog, orders are not placed directly through a catalog interface. Instead, goods are ordered through the web-based procurement system of each company that accesses the catalog as a web service. Most companies have their own budgeting and approval procedures for orders and their own ordering process must be followed when an order is placed. 29
- 30. Catalog Services Service requirements Specific version of catalogue should be created for each client Catalogue shall be downloadable The specification and prices of up to 6 items may be compared Browsing and searching facilities shall be provided A function shall be provided that allows the delivery date for ordered items to be predicted Virtual orders shall be supported which reserve the goods for 48 hours to allow a company order to be placed 30
- 31. Catalogue Non-functional Requirements Access shallbe restricted to employees of accredited organisations Prices and 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 31
- 32. Functional descriptions of catalog service operations OperationDescription Make Catalog Creates a version of the catalog tailored for a specific customer. Includes an optional parameter to create a downloadable PDF version of the catalog. Compare Provides a comparison of up to six characteristics (e.g., price, dimensions, processor speed, etc.) of up to four catalog items. Lookup Displays all of the data associated with a specified catalog item. 32
- 33. Functional descriptions of catalog service operations OperationDescription Search This operation takes a logical expression and searches the catalog according to that expression. It displays a list of all items that match the search expression. CheckDelivery Returns the predicted delivery date for an item if ordered that day. MakeVirtualOrder Reserves the number of items to be ordered by a customer and provides item information for the customer’s own procurement system. 33
- 34. Legacy system services Animportant application of services is to provide access to functionality embedded in legacy systems which reduces the cost of service implementation External applications can access this functionality through the service interfaces
- 35. Software Development with Services Existingservices are composed and configured to create new composite services and applications The basis for service composition is often a workflow Workflows are logical sequences of activities that, together, model a coherent business process For example, provide a travel reservation services which allows flights, car hire and hotel bookings to be coordinated 35
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- 38. Construction by composition Design outlineworkflow In this stage of , you use the requirements for the composite service as a basis for creating an ‘ideal’ service design. Discover services During this stage, you search service registries or catalogs to discover what services exist, who provides these services and the details of the service. Select possible services Your selection criteria will include the functionality of the services offered, the cost of the services and the quality of service offered. 38
- 39. Construction by composition Refine workflow. This involves adding detail to the abstract description and perhaps adding or removing workflow activities. Create workflow program During this stage, the workflow design is transformed to an executable program and the service interface is defined.You can use a conventional programming language, such as Java or a workflow language, such as WS-BPEL. Test completed service or application The process of testing the completed, composite service. 39
- 40. Workflow design & implementation WS-BPEL is an XML-standard for workflow specification. However,WS-BPEL descriptions are long and unreadable Graphical workflow notations, such as BPMN, are more readable andWS-BPEL can be generated from them 40
- 41. Service Testing Testingis intended to find defects and find if a system meets its functional and non-functional requirements. 41
- 42. Service testing problems Externalservices may be modified by the service provider thus invalidating tests which have been completed. The non-functional behavior of the service is unpredictable because it depends on load. If services have to be paid for as used, testing a service may be expensive. 42
- 43. Key points Theservice engineering process involves identifying candidate services for implementation, defining the service interface and implementing, testing and deploying the service. Service interfaces may be defined for legacy software systems which may then be reused in other applications. Software development using services involves creating programs by composing and configuring services to create new composite services. Service software testing. 43
- 44. References • Somerville ,SOFTWARE ENGINEERING Ninth Edition • Len Bass , Paul Clements , Rick Kazman Software Architecture in Practice ,second edition • http://www.codeproject.com/ • http://www.ibm.com/developerworks/rational/libr ary/feb06/eeles/ • https://msdn.microsoft.com/en- us/library/ee658098.aspx
Editor's Notes
- #5 All Processing in Single Computer All Resources Attached to the same Computer Access Via Dumb Terminals
- #7 Two alternatives approaches: Client tier leads to Fat clients Must be reimplemented on each type of client Each software update must be redistributed Data tier leads to Different applications have different needs for the same data Performance issues due to resource (data) usage; e.g. concurrency
- #8 Increase in the number of tiers means: Increase flexibility, functionality and ways of distribution. However: Increases communication costs. Complexity rises leading to higher cost and risk. Increases in duplication can lead to redundancy.
- #13 Above figure encapsulates the idea of a SOA. Service providers : design and implement services and specify the interface to these services. They also publish information about these services in an accessible registry. - Service requestors : (sometimes called service clients) who wish to make use of a service discover the specification of that service and locate the service provider. They can then bind their application to that specific service and communicate with it, using standard service protocols.
- #14 1. SOAP this is a message interchange standard that supports the communication between services. It defines the essential and optional components of messages passed between services. 2. WSDL The Web Service Definition Language (WSDL) is a standard for service interface definition. It sets out how the service operations (operation names, parameters, and their types) and service bindings should be defined. 3. WS-BPEL The Web service Business Process Execution Language This is a standard for a workflow language that is used to define process programs involving several different services.
- #15 1. SOAP this is a message interchange standard that supports the communication between services. It defines the essential and optional components of messages passed between services. 2. WSDL The Web Service Definition Language (WSDL) is a standard for service interface definition. It sets out how the service operations (operation names, parameters, and their types) and service bindings should be defined. 3. WS-BPEL The Web service Business Process Execution Language This is a standard for a workflow language that is used to define process programs involving several different services.
- #16 This example illustrates one of the key advantages of the service-oriented approach. It is not necessary to decide when the system is programmed or deployed what service provider should be used or what specific services should be accessed.