sfwr eng 3a04: software design ii · 2017-03-08 · sfwr eng 3a04: software design ii dr. r. khedri...

SFWR ENG 3A04:Software Design II

Dr. R. Khedri

OutlineSFWR ENG 3A04: Software Design II

Dr. Ridha Khedri

Department of Computing and Software, McMaster UniversityCanada L8S 4L7, Hamilton, Ontario

Term 1

Acknowledgments: Material based on Software Architecture Design by Tao et al. (Chapter 10)

Dr. R. Khedri SFWR ENG 3A04: Software Design II


Dr. R. Khedri

Outline

Part I: Review ofPrevious Lecture

Part II: Today’sLecture

Outline of Part I

1 Model-View-ControllerMVC-IMVC-ll

2 Presentation-Abstraction-Control (PAC) Architecture



Dr. R. Khedri

Outline

Part I: Review ofPrevious Lecture

Part II: Today’sLecture

Outline of Part II

3 Overview

4 Client/Server

5 Multi-tier

6 Broker Architectural Style

7 Service-Oriented Architecture (SOA)



Dr. R. Khedri

Model-View-Controller

Presentation-Abstraction-Control (PAC)Architecture

Part I

Review of Previous Lecture



Dr. R. Khedri

Overview

Client/Server

Multi-tier

BrokerArchitectural Style

Service-OrientedArchitecture (SOA)

Part II

Today’s Lecture



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed Architecture Overview

A distributed system is a collection of computersconnected through a communication network

Data is distributedSoftware is distributedUsers are distributed

The sub-systems or components within a distributedsystem communicate with each other via

message passingremote procedure callremote method invocationetc.



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Two important issues for designing a distributed system are:

Topology: the way in which entities connect with eachother

Mode: the method by which they communicate witheach other

SynchronousAsynchronousmessage drivencallbackevent-driven



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed ArchitectureClient/Server

Figure: Examples of network topologies



Dr. R. Khedri

Overview

Client/Server

Multi-tier




A distributed system can be modeled as a

Client/server architecture

Broker architecture

Service-Oriented Architecture (SOA)

The important features of a distributed architectureinclude

its service location transparency

service reliability and availability



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed Architecture Client/Server

The client-server model is the most commondistributed system

It is based on two communicating subsystems (usuallyrunning on different processors)

Client issues a request to the second process server

Server process receives the request, carries it out, andsends a reply to the client



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed ArchitectureClient/Server

Figure: Two tier client/server architecture



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed Architecture Client/Server

AdvantagesSeparation of responsibilities such as user interfacepresentation and business logic processing

Reusability of server components

DisadvantagesLack of heterogeneous infrastructure to deal with therequirement changes

Security complications

Server availability and reliability

Testability and scalability

Fat clients



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed Architecture Multi-tier

The front tier in a multi-tier architecture is the userinterface presentation tier

The middle-tier(s) take(s) care of business logic,application decision, and execution

The back-end tier usually works on databasemanagement, or on a (virtual) machine

The advantages of multi-tier over the two-tierarchitecture are

the enhancement of reusabilityscalability by the middle tier

The middle tier can also provide multi-threadingsupports for scalability

Multi-tier architecture also reduces the traffic on thenetwork

Disadvantage: complex testability



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed ArchitectureMulti-tier

Figure: Three tier architecture



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed ArchitectureBroker Architectural Style

The broker architecture is a middleware architecturewidely used in distributed computing

It is suitable for distributed computing that coordinatesand facilitates communication

brokering the service requestslocating proper serverforwarding and dispatching requestssending responses or exceptions back to clients

It can be used to structure distributed software systemswith decoupled components that interact by remoteservice invocations

The most important quality of this architecture =better decoupling between clients and servers



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Servers make their services available to their clients byregistering and publishing their interfaces with thebroker

Clients can request the services of servers from thebroker statically or dynamically by look-up

A broker acts as a policeman in a busy intersectionwho controls and interacts with the client componentsand server components

The connection between clients and servers ismaintained by the broker



Dr. R. Khedri

Overview

Client/Server

Multi-tier




A distributed client can access distributed servicessimply by calling a remote method of a remote object

This concept is similar to unix Remote Procedure Call(RPC) and Java Remote Method Invocation (RMI)

The clients can dynamically invoke the remote methodseven if the interfaces of the remote objects are notavailable at the compilation time



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Client has a direct connection to its client-proxy

Server has direct connection to its server-proxy

The proxy talks to the mediator-broker

The proxy is a well known pattern for hiding low-leveldetailed communication processing

It intercepts the client’s requestgets all argumentspackets itmarshals (streamlines) and formats the package in theformat of communication protocolsends it to the broker

A broker system is also called proxy-based system



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Sub-components of a broker architecture

BrokerStub (client-side proxy): It mediates between client andbrokerSkeleton (server-side proxy)

It is statically generated by the service interfacecompilation and then deployed to the server sideIt receives the requests, unpacks the requests,unmarshals the method arguments, and calls theappropriate serviceIt also marshals results from the sever before it sends itback to the client

Bridges (Optional)Used to hide implementation details when two brokersinteroperateCan connect two different networks base don differentcommunication protocols



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Broker model



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Connected brokers with client/server proxy



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Class diagram for broker architecture



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Sequence diagram for broker architecture



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Advantages

Server component implementation and locationtransparencyChangeability and extensibilitySimplicity for clients to access server and serverportabilityInteroperability via broker bridgesReusabilityFeasibility of runtime changes of server components(add or remove server components)

Disadvantages

Inefficiency due to the overhead of proxiesLow fault-toleranceDifficulty in testing



Dr. R. Khedri

Overview

Client/Server

Multi-tier



Distributed ArchitectureService-Oriented Architecture (SOA)

A service is a business functionality that iswell-defined and self-containedindependent from other servicespublished and available to be used via an interface

SOA services can be reused extensively regardless ofwhether they are based on new or legacy applicationsLoose coupling of service-orientation architectureprovides a great flexibility for enterprises to make useof all available service resourses

The connections between services are conducted bycommon and universal message oriented protocols suchas the SOAP Web service protocolA connection can be established statically ordynamically



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Client with services and service directory



Dr. R. Khedri

Overview

Client/Server

Multi-tier




A service-oriented application might make use of manyavailable services

For that one needs a flow control language

allows specifying the sequence and logical order of thebusiness executions based on the business logic

Some services can be reused by other applications thatthey are not originally designed for

We can build a new service out of existing services

aggregation: extends one endpoint of a service to makea new interface of the new servicecontainment structure: has one interface that wraps allused services

Services can be recursively constructed to satisfy amore complex business needs (through aggr. and cont.)



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Service composition



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Service reuse



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Service composition model



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Figure: Service working model



Dr. R. Khedri

Overview

Client/Server

Multi-tier




Advantages of SOA

Loosely-coupled connection

Each service component is independent from otherservices due to the stateless service feature

Interoperability: Technically any client or any servicecan access other services regardless of their platform,technology, vendors, or language implementations

Reusability: Any service can be reused by any otherservices and service is developed to be reused as well

Scalability: Loosely coupled services make themselveseasy to scale



Dr. R. Khedri

Overview

Client/Server

Multi-tier




sfwr eng 3a04: software design ii · 2017-03-08 · sfwr eng 3a04: software design ii dr. r. khedri...

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