Service Layers

Service Layers

605.702 Service Oriented ArchitectureJohns-Hopkins University

Montgomery County Center, Spring 2009Session 6, Lecture 6: March 4, 2009

Instructor: T. Pole

Agenda• Required Reading for This Week

• Chapter 9: Service Layers

• Today’s Presentation– Update on Chapter 8

– Today’s Lecture• Text CH 9

– Class Assignments • Exercise #4, Implementing a Service Composition

– Review for Mid Term Exam• Mid Term is next week Wednesday March 11, 2009

Ch 8 Principles of Service Orientation

• Additional notes on Chapter 8 have been added to the lecture notes for last week, Lecture 5 2/25/09

• Check these notes in reviewing for the mid term exam next week

Chapter 9: Service Layers

• 9.1 SO and Contemporary SOA– Review table 9.1: how SOA characteristics are influenced by

Web Service specs and SO principles• 9.2 Service Layer Abstraction

– The service layer is between the application layer and the business process layer (see Ch 8)

– The implementation of the service interface layer is sub-divided into layers following one of several different models

• 9.3 Application Service Layer• 9.4 Business Service Layer• 9.5 Orchestration Service Layer• 9.6 Agnostic Services• 9.7 Service Layer Scenarios

9.2 Service Layer Abstraction

• Figure 9.2 shows the SOA layers WITHIN the single Service Interface Layer of the Enterprise Architecture – Business Process Layer

Processes of the Enterprise, not just the IT systems– Service Interface Layer

• Orchestration Layer• Business Service Layer

– NOT the Business Process Layer• Application Service Layer

– NOT the Application Layer

– Application LayerLegacy and Service Implementations

9.3 Application Service Layer

• Sits within the Service Interface Layer, and integrates with the Application Layer below

• Solution (Meaning business process) agnostic, are more generic and usually reusable across multiple biz processes

• Can also be used to integrate other application services

• Mixture of custom and COTS products• Hybrids may cross the line between business

and application logic

9.4 Business Service Layer

• Business services can be mapped to small grained or low level specific business processes and entities

• Business oriented services can be– Entity Centric – Task Centric– Not both, but a business service layer can be

a mix of both. Usually will be primarily one or the other

9.5 Control or Orchestration Service Layer

• Introduces another type or service, the process service (aka but not synonymous with the controller service)

• Directly relates to a business process• Controls other business, hybrid and

application/utility services to automate a process

• Can be implemented in “non-technical” languages, e.g. BPEL

9.6 Agnostic Services

• Agnostic in this context can mean not bound to any one process– e.g. an entity based service can be used by

multiple biz processes that involve that entity– e.g. a utility service is by definition a generic

reusable service not bound to any business entity: task or entity based

• Exist with the application service layer or the business layer

9.7 Service Layer Scenarios

• There is no one layered model for the Service Interface Layer, some options are:– Single hybrid layer

• Common, doesn’t evolve well, brittle– Hybrid over utility

• Also common among mature software developers, reuse driven– Biz task centric over utility

• Often the goal for mature business centric developers– Task centric over entity centric over utility

• Common among mature systems, flexible, adaptable– Orchestration over hybrid over utility

• Better then single hybrid, but extending to new orch. difficult– Orchestration over task centric over utility

• Flexible, evolves well, flexibly adjusts to change

Exercise #4: Implementing a Service Composition

SEAM Index ------------------

Register Asset FindAsset

ClassifyAsset

DocManager ------------------

StoreDoc GetDoc

ClassifyAsset

TextIndexer ------------------

IndexDocQueryIndex

TestConsumerUI

Exercise #4 Interface: Services and Operations

• SEAMIndex Service (New Service and Functions)– AssetID RegisterAsset( string AssetAsText )– AssetID FindAsset( string Title, string Author )– bool ClassifyAsset( string AssetID, string Class)

• TextIndexer Service (Wraps Legacy Component)– Bool StatusFlag IndexDoc( string DocAsText )– AssetID[] QueryIndex( string Title, string Author )

• DocManager Service (Wraps Legacy Component)– AssetID StoreDoc( string DocContent )– string GetDoc( string DocID )– bool ClassifyDoc( string DocID, string Classification )

Legacy Components API

• Supplied as C# Functions– TextIndexerAppLibrary

• bool IndexTerms( string Content )• String FindDocs( string Title, string Author )

– DocManagerAppLibrary• string Store( string DocContent )• string Retrieve( string DocID )• bool Categorize( string DocID, string Category )

Integrating Legacy Apps

• Download complete applications assemblies from class web site– Integration Stubs available now– Fully functional projects will be published next

week

• Add as projects to your solution

Review for Mid Term Exam

• Review of the previous lectures

• Q&A for Chapters 1 – 9

• Review of Implementing Web Services and SOA Designs in Visual Studio/ASP.Net

• Additional Notes

SOA Implementation via Web Services in ASP.Net

• Exercise #1: Web Service Consumers– Web Reference

• What is it doing?• What is its purpose?

• Exercise #2: Building a Web Service– What does a Visual Studio Web Service

project generate?

• Exercise #3: Publishing a Web Service– What is published to the remote site?

Additional Notes: Service Oriented’ness

• When designing a service oriented architecture, ask yourself:– Is communication among services and consumers like a phone

conversation or the exchange of standard forms– If it is like a phone call interview, it is chatty and not service

oriented.• A service is being performed, but each interaction in the system is

only a piece of the complete service

– If it is like an exchange of standard forms, and all the information required to perform the service is on that single initial form, and the information required is returned in a equally complete single form, it is service oriented

• Example: You need to determine if several checks you’ve written have cleared the bank.

Not Service Oriented

• Call the bank, the operator ask what your need is.

• You respond you wish to verify if these checks have cleared

• They ask you to identify your account and your person.

• They validate your identity and ask which checks: which numbers and what dates.

• You give them the check information, one check at a time.

• They verify each one at a time.

Service Oriented

• You fill out a form which includes your account information, personal identifiers, the service you want performed (verify checks have cleared), and the numbers of the checks.

• The response is another form listing the state of all the checks you have asked to have verified.

The Difference?

• They both perform the same business process

• They both have the same accuracy and completeness

• One is a complete service performed in one single step, and is service oriented

• The other is performed by many related interdependent steps, and is not

Summary• Session 7: 3/11/09

– Mid Term Exam

– Introduction of Class Week

• Spring Break the following week– Exercise #4 is due 3/25/09

– Specifications for Class Project will be presented