Service Oriented ArchitectureA High Level Breakdown

for COMP 410 by Dennis QianSource: SOA with .NET & Windows Azure, Thomas Erl

What is Service-Oriented Computing?

• New generation of distributed computing platform

• Has its own design paradigms, principles, patterns, models, etc.

• Creation of solution logic units individually shaped so that they can be collectively and repeatedly utilized

Eight Design Principles of service-orientation paradigm

Standardized Service Contract

Service Loose Coupling

Service Abstraction

Service Reusability

Service Autonomy

Service Statelessness

Service Discoverability

Service Composability

Service Loose Coupling

Service Abstraction

Service Composability

Standardized Service

Contract

Service Reusability

Service Autonomy

Service Statelessness

Service Discoverability

SERVICE

Implement a standardized contract

Minimize dependencies

Implement generic and resusable logic and contract

Minimize the availabilityof meta information Independent functional

boundary and runtime env.

Adaptive and state management-free logic

Maximize composability

Implement communicativemeta information

A Service

• Container of capabilities associated with a common purpose

• Neutral to technology platform• Component – part of a distributed system• Web Service – XML Schema, confusing shit

Service Models

• Service model – classification indicating type of service based on its logic– Task Service – non-agnostic so general single-

purpose, parent business process logic, usually has logic to spawn other services

– Entity Service – reusable, agnostic, associates with one or more related business entities

– Utility Service – reusable, agnostic, low-level technology-centric functions, not derived from business specifications, notification/logging/security

Distributed Computing --> Service Oriented Computing

• Computing has moved from procedural programming -> object-oriented programming, and then from OOP -> service-oriented programming

• Distributed architecture met evolving demands that client-server architecture was unable to handle, n-tier, service-oriented arch. extends on distributive architecture

Service Contracts(basically interfaces for our services)

using System;using System.Service Model;namespace HelloWorld{ [ServiceContract] public interface IGreetings { [OperationContract] string Greet1(); }}

-----

[MessageContract]public class ContractMessage { [MessageHeader] public MsgHeaer msgHeader; [MessageBody] public MsgBody msgBody

-----

<system.serviceModel> <services> <service name=“AccountService”> <endpoint name=“EndPoint1” address=“net.tcp://localhost:1234” binding=“netTcpBinding” contract=“Iaccount” /> </service> </services></system.serviceModel>

- Corresponds to ServiceContract attribute

- Composed of an interface contract and a service endoint

- Interface Contract – subset of service contract comprised of the operation contract, data contract, and message contract

- Operation Contract - method or capability as part of interface contract

- Data Contract – means of expressing data models ie, XML schemas are data contracts

- Message Contract – pretty much message protocol

- Service Endpoint – cormprised of address, binding, and contract parts

Contract-First approach

• Create or Reuse Data Contract• Create Message Contract• Create Interface Contract• allows for standardized service contracts

(possibly on industry standards etc.)• Canonical Schemas // XML Schemas //

establishes structure and validation rules, can also define data models

Data Model Transformation

• avoid this shit at run time, which is why we used Standardized Service Contract principle

• example: services encapsulating legacy systems inevitably need to transform data between legacy data models and standardized data models

• Service B : schema1 -> transform schema -> schema2 : Service A

Data Model Transformation

• three ways to apply DMT– object-to-object – XML message serialized into

object, translated into another object, serialized back into XML

– LINQ-XML – irrelevant– XSLT Transformation - irrevenat

Canonical Protocol

• use the same communication protocol within a service inventory boundary (like TCP for all our module comms)

• Dual Protocol – easy because we can just add additional endpoints, allows for primary/secondary protocols say to optimize for performance issues

Canonical Expression

• obvious but worth mentioning• have uniform naming conventions when it

comes to service contract definition• ie. GetOrderStatus() synonymous with

RetrieveStatisticsPerOrderMode(), so just be consistent: GetOrderStatus(), GetStatisticsPerOrderStatus()

*** Service Loose Coupling ***

• goal of this principle is to allow service to develop and evolve with minimal impact on each other

Service Loose Coupling

• logic-to-contract coupling – internal service logic to service contract, positive, preserves contract’s independence from implementation

• contract-to-logic coupling – opposite ^, negative, because changes to logic impact service contract, and consequently also impact service consumers who depend on contract

• contract-to-technology coupling – similar ^, negative, forces service consumers to bind to platform-specific technology protocol

• contract-to-implementation coupling – negative, directly expressing characteristics of implementation within the contract

• contract-to-functional coupling – negative, occurs when general logic is designed with a particular consumer in mind, contract can become dependent on underlying functionality

• consumer-to-implementation coupling – negative, consumer bypasses contract to direct access implementation

• consumer-to-contract coupling – positive, consumers have limited access to the service contract

- goal of this principle is to allow service to develop and evolve with minimal impact on each other

- determines how the contract is architecturally positioned

- advocates reducing dependencies between service consumers and the service contract, as well as b/w the service contract and the underlying service implementation

- positive and negative types of coupling

core service logic

service consumers

SC

underlying service logicis coupled to theservice contract

consumers are coupledto the service contract

service contract is physically decoupled

Service Façade[Service Contract]interface IPersonService{ [OperationContract] person GetPerson(int personId);}

//façade1class PersonService: IPersonService{ public person GetPerson(int personId) { return ServiceImplementation. GetPersonById(personId); }}

//facade2class SimplePersonService : IPersonService{ public person GetPerson(int personId) { var person = ServiceImplementation. GetPersonById(personId); person.address = null; return person; }}

class ServiceImplementation{ public static person GetPersonById(int personId) { return new person{ id = personId }; }}

- when pursuing logic-to-contract coupling, additional coupling flexibility can be built into the service architecture by establishing additional layers of implementation logic

- advocates the positioning of a façade components between the contract and core service logic

- protects the core service logic from changes to the contract, or concurrent contracts

- typically contains code that:- chooses which methods or

functions to call in the core implementation

- compensates for changes in logic to retain coupling

- allows logic to remain physically separate and stable should contract change

core service logicservice façade logic

SC

façade logic is coupledto core logic

façade logic is coupled to contract

changes to the contractimpacts façade logic

core logic is decoupledfrom contract and may

therefore not be affectedby the change

Concurrent Contracts• enables a service to have more than one service

contract in order to accommodate different service consumers

core service logic

service façade

logic : ASC: A

service façade

logic : BSC: B

Service Reusability – identification of reusable logic

• Separation of Concerns • Functional Decomposition• Service Encapsulation – after above, leads to

below• Agnostic Context, single/multi-purpose logic • Agnostic Capabilities

Service Composition• Aggregate of services composed to automate

a particular task• common objective among all SOA design

principles

Service A- Capability A

Service B- Capability A- Capability B

Service C- Capability A- Capability B

Service D- Capability A- Capability B

(1)(2) (3)

(4)(5)

Composition Roles• composition controller – service with capability that is

executing the parent composition logic required to compose capabilities within other services (CP much?)

• composition member – service that participates in a service composition by being composed by another service (FE/Mixers)

• composition initiator – program that initiates a service composition by invoking the composition controller, may or may not exist as a service (control panel :D)

• composition sub-controller – variation of the composition controller role that is assumed by a service carrying out nested composition logic, within a capability that is composing one or more other service capabilities while itself also being composed (Mixer roles and mixer trees)

Service Layers

• based on a fundamental separation of agnostic and non-agnostic service logic

• end up with a task service layer, followed by agnostic service layers

Orchestration• book doesn’t explain it that well, but it’s basically

what were doing when we try to construct our cloud tree/graph/chains in an automated way

• http://en.wikipedia.org/wiki/Orchestration_%28computing%29

• “Stitching of software and hardware components together to deliver a defined Service”

• involves saving state in a State Repository (yeah database)

Topics Worth Exploring

• Service Bus – basically a big messenger utility to establish comms between services– eventing– service remoting– tunneling– message buffers– service registry

• Use of caches – could eliminate some processing• Access Control and cloud security

(marketability/extensibility factor)

Useful Sites

• www.whatissoa.com• www.soaprinciples.com• www.soapatterns.com• www.soa-manifesto.com