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SOA in Action

SOA in Action. Chapter 10 B. Ramamurthy. Motivation. Different usage models for the same service: different protocols for access, different granularity, different access methods and endpoints Different design considerations are needed Typically multiple services are at work

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SOA in Action

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  1. SOA in Action Chapter 10 B. Ramamurthy

  2. Motivation • Different usage models for the same service: different protocols for access, different granularity, different access methods and endpoints • Different design considerations are needed • Typically multiple services are at work • Consider these: does a service need to idempotent? Is it aggregation-friendly? Is it transaction-based or compensation-based? Asynchronous or asynchronous?

  3. Topics • Different application models dictate different requirements: • Web application (10.1) • EAI integration (10.2) • B2B model (10.3) • Fat client model (10.4) • Small mobile device such cellular telephone access to services (10.5) • Multi-channel access to services (10.6)

  4. Web Application • General interaction pattern (fig.10-1) • Browser /web server security model: state maintained by web application (fig. 10-2) • One time transaction (OTT) pattern (fig.10-3) • While layer diagram was good for architectural model, semantics or logic for services interaction cannot be explained using the layer diagram • We will look at sequence diagram and features provided by BPEL for this.

  5. Sequence Diagram for Airline Checkin Web Application

  6. Enterprise Application Integration (EAI) • Classify the applications as service providers and service consumers. Pattern: service provider/ service consumer • Single sign-on, quality of service should be explicitly addressed. • Service enablement strategies: create a service encapsulating the functionality provided by an existing application. • Consider the transformation of a monolithic application into a service-oriented application.

  7. Monolithic application Visual part Non-Visual part Service-enablement Separate visual and non visual parts

  8. Application frontend Application frontend Application interface!#1 Application logic Application Interface#2 Service-enablement Vertical slicing

  9. Service-enablement Application frontend Application interface!#1 Application Interface#2 Observe data encapsulation

  10. Service-enablement (SCA: Services Component Architecture) Services infrastructure (Ex: ESB) Application frontend Service #1 Service #2

  11. Transform Granularity • Transform fine-granular interaction among distributed components into coarse-granular interaction pattern using facades. • See fig.10.5

  12. Granularity of access Application frontend Traditional user interface Façade #1 Façade #2 Services infrastructure

  13. EAI  SOA • EAI can drive an SOA • EAI is excellent driver for service enabling applications • From business perspective EAI is introduced to simplify application infrastructure and to foster reuse. • This is good motivation for resorting to SOA

  14. Stability and Upgradeability • Service stability and upgradeability are two of the most desirable features in an EAI environment. • User and provider in different domains • Backward compatibility • Different versions are supported (see fig 10-6 and 10-7) • EAI requires repositories to ensure stability and upgradeability.

  15. Business-to-Business (B2B) • In a B2B environment a corporation offers some service to another company over the public networks. • Service consumer and provider benefit greatly from standardized protocols. • Standards such as ebXML (UN/CEFACT), and RosettaNet are examples of standardization effort. • Business process can be stateful, but services invocations can be stateless by using token identifying an interaction. • Typical characteristics: stateless, location transparency, trusted domains

  16. B2B • Stateless: enables interaction with remote customers over connections with high network latency. Much fewer constraints on the caller applications. • Location transparency: real location transparency using service repositories. Change is a location of a service need to be updated only in the registries, caller need not be aware of this. • Consider airline ticket with multiple legs of journey (Scenario is explained very nicely pp218-219) • Send to the request to trusted airline partner (Apply when weak connectivity) • Frequent synchronization with partners (infrequent usage) • Partner 1 is service consumer of services offered by partner 2 ( stable connectivity, frequent usage) • Service level agreements provides a mechanism for negotiation, guarantees, monitoring and enforcement of agreements. (See: web services standards WS-SLA)

  17. Fat Clients (Better: Rich Clients) • Rich Interface Applications (no need to install an .exe/xyz.war file to run an application) • Ex: Google maps, mapquest • Clients trusted by the local environment • Check-in kiosk is a fine example

  18. Rich Client Example Checkin Kiosk Luggage Scale Boarding Pass printer Luggage tag printer Card Reader Customer service Checkin service Ticket service

  19. Designing for smaller devices • How do you define a small device? Small footprint operating system, small screen (150X100 pixels), limited processing capability, small memory 256KB, limited data entry, connectivity to enable periodic synchronization with base and facilitate participation in an SOA. • Lightweight security: information available on an identifier embedded in the device such as …

  20. Smaller devices in an SOA • Decouple the service invocation in the device from the actual service using an adapter that resides at a gateway server. Ex: SMS (short message service) messaging instead of soap messaging until the gateway; gateway may translate into SOAP payload semantics to the actual service. MMS (Multimedia Service) is a successor of SMS

  21. Multi-channel Applications • A multi-channel application is characterized by a functional core that can be accessed through different channels by either humans or other programs.

  22. Multi-channel applications

  23. Multi-channel application • Start with fundamental SOA: only two layers: Enterprise layer with all the application frontends for the various channels and basic functional layer (fig. 10-16) • Lean service approach • A façade can be added at intermediary layer (fig. 10-17) • Façade manages the heterogeneity of underlying layers • If every channel requires its own channel-specific processing add a process layer with one service per frontend (fig. 10-19) • Every channel requires its own process

  24. Summary • Use scenario diagram (UML standard) to discuss semantic flows among services • We discussed scenarios where an SOA can be beneficial. • Provide a service with a number of interfaces and protocols and design the service with the requirements specified by the customer.

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