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1) Web Service & SOA

Web Service & SOA

QuestionAnswer
System Integration the task of making different applications work together to produce a unified set of functionality.
Why System Integration To support common business processes and data sharing across applications:
Challenges – custom developed in house or purchased from third-party vendors. – run on multiple computers (multiple platforms, and maybe geographically dispersed) – not have been designed with integration in mind and are difficult to change
More Challenges – Networks are unreliable&slow – every app is different (pr language, O/S, data format),integration solution must interface with all these technologies – Change is inevitable (apps change over time),dependencies must be minimized using loose coupling
Service-Oriented Paradigm The service-oriented paradigm to programming utilizes services as the constructs to support the development of rapid, low-cost and easy composition of distributed applications.
Web Service a self-describing, self-contained software module available via a network, which completes tasks, solves problems, or conducts transactions on behalf of a user or application,can be discovered using UDDI,HTTP and XML is the basis for Web services
Services Composing applications by discovering and invoking network-available services rather than building new applications or by invoking available applications to accomplish some task.
Direct Processing Client waits until request is serviced. Service provided as quickly as possible and result is returned. Client and server are synchronized.
Queued Processing Request enqueued and client continues execution. Server dequeues request at a later time and enqueues result. Client dequeues result later. Client and server unsynchronized.
Queued Processing Advantages – Client can enter requests even if server is unavailable – Server can return results even if client is unavailable – Request will ultimately be served even if T2 aborts (since queue is transactional)
Remote Procedure Call (RPC) Semantics can include: – notion that computation may fail (e.g., errors, faults, deadlocks) – blocking or non-blocking – synchronous vs. asynchronous – at least once, at most once, exactly once
RPC infrastructure must implement – Server Registration, Binding, Marshalling, Message Send/Receive
Server Registration • Use Discovery or Directory Service • Each server registers a service and a version – Service - typically implemented as an integer; a set of well-known services exist – Version - a number used to select which server to use – issue: Load Balancing
Marshalling • Assume heterogeneous computing environment • Need to have a consistent set of data types • What about pointers? • What about exceptions? – Exceptions can result from errors at the client site or network problems
Client stub – Locates server - sends globally unique name (character string) provided by application to directory services – Sets up connection to server – Marshalls arguments and procedure name – Sends invocation message (uses message passing)
Server stub – Unmarshalls arguments – Invokes procedure locally – Returns results
Connection Set-Up: IDL • Server publishes its interface as a file written in Interface Definition Language (IDL). • IDL compiler produces header file and server specific stubs • Client stub linked to application
Directory Services • Directory (Name) Services provides run-time rendezvous. – Server registers its globally unique name, net address, interfaces it supports, protocols it uses, etc. – Directory service responds with address, protocol
RPC: Failures – Possible reasons: communication slow, message lost, server crashed, server slow – Possible actions: resend message, contact different server, abort client, continue to wait – Problem: different actions appropriate to different failures
ASP (Application Service Provider) – An ASP hosts the entire application and the customer has little opportunity to customize it beyond the appearance of the user interface – An alternative:ASP is providing a software module that is downloaded to the customer’s site on demand+web
Informational Services services of relatively simple nature. They either provide access to content interacting with an end- user by means of simple request/response sequences, or expose back-end business applications to other applications. Examples include:
Complex services involves many pre-existing services possibly found in diverse enterprises to complete a multi-step business interaction:Coarse-grained communication implies larger and richer data structures and enables looser coupling, asynchronous communication
functional service description details the operational characteristics that define the overall behavior of the service., e.g., how to invoke service, and location where it’s invoked
non-functional service description targets service quality attributes,e.g., service metering and cost, performance metrics (response time or accuracy), security, authorization, authentication, scalability, availability, etc.
Stateless or stateful services: Services that can be invoked repeatedly without having to maintain context or state they are called stateless.
Loose coupling – Coupling indicates the degree of dependency any two systems have on each other – Web services are loosely coupled: they connect and interact more freely (across the Internet). They need not know how their partner applications behave or are implemented
Service Interface the operations available, the parameters, data-typing and the access protocols, in a way that other software modules can determine what it does, how to invoke its functionality, and what result to expect in return.
Service Implementation The service implementation realizes a specific service interface whose implementation details are hidden from its users.
Client perspective - What does it do - How do I use it - Where can I find it?
Provider perspective - How to represent it - How to build it - Where to host it - How to publish it
What is behind a provided web service interface - Web service orchestration interface - Imported constituent interfaces (outsourced, inhouse)
Service Model allows for a clear distinction to be made between
Service Providers organizations that provide the service implementations, supply their service descriptions, and provide related technical and business support
Service Clients end-user organizations that use some service) – service registry (a searchable directory where service descriptions can be published and searched
Service-Oriented Architecture SOA is a logical way of designing a software system to provide services to either end-user applications or to other services distributed in a network, via published and discoverable interfaces.
Layers in SOA 1) Business domain 2) Business processes 3) Business services 4) Infrastructure services 5) Component based service realizations 6) Operational systems
Web Services Technology Stack 1) UUID - Discovery 2) WSDL - Description 3) SOAP - Message 4) XML - Message 5) HTTP, JMS, SMTP - Transport
Quality of Service QoS refers to the ability of a Web service to respond to expected invocations and perform them at the level commensurate to the mutual expectations of both its provider and its customers.
Service Level Agreements contract between a provider and client, formalizing the details of use of a Web service (contents, price, delivery process, acceptance and quality criteria, penalties, etc. in measurable terms), mutual understandings and expectations
Created by: timeakiss