25977233 Component Based Software Engineering

8/3/2019 25977233 Component Based Software Engineering

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By:

Harshpreet Singh(ME SoftwareEngg. 1st yr )

Thapar University


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Szyperski: A software component is a unit of composition with contractually specified

interfaces and explicit context dependencies only. A software componentcan be deployed independently and is subject to composition by third-parties.

Councill and Heinmann: A software component is a software element that conforms to a

component model and can be independently deployed and composedwithout modification according to a composition standard.

(explicit context dependencies)

(reusable, independent deployment, composition)

A thing is not a component if it cannot be reused across multipleapplications (but it may be a module)

Single-product development (which does not develop with reuse in mind), atbest, has a remote change of yielding components, if their units are accidentlydeveloped as reusable unitsBut single-product development can reuse existing components

Development from scratch, by definition, does not reuse


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Developing with reuse / developing for reuse Single-product development, by definition, does not involve

development for reuse

The day that we no longer need to develop for reuse is

The day that the software engineering problem (software crisis)is solved The day that software engineers and researchers lose their jobs

In the mean time, essence of CBSE: development for reuse Development with reuse may be used to achieve development

for reuse, but often this is not feasible Components are developed for reusability


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CBSE assumes the existence of 2 component development

paradigms

Single-product development Top down, single architecture driven Planned use of components (develop only what is needed) All development within a single organization

All software developed during the process

Component market (e.g. Components Off The Shelf) Bottom-up (no global architecture defined) Use of components is opportunistic (use whatever is available) Component software is available when starting the project

It results in inter-organizational reuse

Single-product development: problems of standard software engineeringprocess Component market: problems are not so obvious. After all, this is supposedlythe goal of CBSE.


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Independentcomponents (specified bytheir interfaces.)

Component standards

(to facilitate componentintegration)

Middleware(that providessupport for component inter-operability)

A developmentprocess(that is geared toreuse)


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Provides interface Defines the services that

are provided by thecomponent to othercomponents.

Requires interface Defines the services that

specifies what servicesmust be made available for

the component to executeas specified.

Requires

provides


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A contract specifies the interactions among components,in terms of: The set of participating components;

The role of each component through its contractual obligations;

The invariant to be maintained by the components;

The specification of the methods which instantiate the contract. A contract is comprised of:

The Invariant, the global constraints which the component willmaintain;

The Pre-condition, the constraints which need to be met by the client;

The Post-condition, the constraints which the component promises toestablish in return.


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Patterns define recurring solutions to recurring problemscapturing non-obvious solutions, not just abstract principles orstrategies. A component, as a reusable entity, can be seen as a realization of some

design pattern.

Patterns can be classified into three major categories:

Architectural Patterns, capture the overall structure and organization ofa software system.

Design Patterns, refine the structure and the behavior of the

subsystems ,components of a software system, and the relationshipsbetween them.

Idioms, are low-level patterns which are dependent on chosen paradigm& programming language used.


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CBSE means that we build software by "putting piecestogether". Frameworks provide the context in which thepieces can be used.

A Component Frameworkdescribes a circuit-board

with empty slots into which components can be insertedto create a working instance.


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A Component Model is a definition of standards for

component implementation, documentation and deployment.

The component model specifies how interfaces should bedefined and the elements that should be included in aninterface definition.

Comp onent model

InterfacesUsage

informationDeployment

and use

Interface

definition

Sp eci fic

interfaces

Composition

Namingconvention

Meta-data

access

Customisation

Packaging

Docu mentation

Evolution

support

Elements ofcomponent model


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Platform services

AddressingInter face

definition

Component

communications

Exception

management

Horizontal services

Security

Transaction

management

Concurrency

Component

management

Persistence

Resource

management


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Types of compositiono Sequential compositionwhere the

composed components are executed insequence. This involves composing theprovided interfaces of each component.

o Hierarchical compositionwhere onecomponent calls on the services ofanother. The provides interface of onecomponent is composed with the requires

interface of another.

o Additive compositionwhere theinterfaces of two components are puttogether to create a new component.

Composition involves integrating components with each other andwith the component infrastructure.


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Address the problem of component incompatibility byreconciling the interfaces of the components that arecomposed.

Different types of adaptor are required depending on the typeof composition.

An addressfinder and a mapper component may becomposed through an adaptor that strips the postal codefrom an address and passes this to the mapper component.

Data co llector

addSensorremoveSensorstartSensor

stopSensor

testSensor

listAll

repor t

initialise

sensorManagement

sensorData

Adaptersensor

start

getdata

stop

An example


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Trust. You need to be able to trust the supplier of acomponent. At best, an untrusted component may notoperate as advertised; at worst, it can breach your security.

Requirements. Different groups of components will satisfydifferent requirements.

Validation. The component specification may not be detailed enough

to allow comprehensive tests to be developed. Components may have unwanted functionality. How can

you test this will not interfere with your application?


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ComponentSpecification and collaboration is often too low level, missing many of high level

functional and non-functional requirements

Service componentSpecified in terms of interfaces which are parts of a contract (formally describing howprovided interfaces behave with required interfaces)

Interface behavior/obligation specified in terms of Service Level Agreement (SLA)

Characteristics Large granularity (provides single business concept or process) Asynchronous interaction (message-based, not call-and-return) Interface specification behavior fully defined as a state machine of messages

Business protocols

Business protocol = subset of business process describing the message exchangestate machine of each party

Challenges of designing a protocol (deadlocks, livelocks, reliability, sequencing, etc.) Contracts implement business protocols

Parameterized schemas (e.g. Buyer/Seller contract, with Buy and Seller as variation points)


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Service-Oriented Architecture (SOA) A topology of loosely coupled, large granularity service components Message-based contracts (bi-directional, asynchronous)

Web services (implementation of SOA) Features

Location independent (write once, run anywhere) Internet standards (open, intranet, internet) True black-box (message interchange) No explicit programming model (connection is the common vocabulary)

Specification (Web Service Description Language) Web service data semantics

XML schemas (XMI) for data format standard Standard dictionary of terms

Semantic web (data reuse framework using Resource DescriptionFramework uses XML for syntax and URIs for naming)

Web services process semantics Language for expressing contracts (Message Exchange Patterns) Business Process Execution Language (BPEL) for web services

Specify how a group of web services work to implement a business process


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When composing components, you may findconflicts between functional and non-functionalrequirements, and conflicts between the need forrapid delivery and system evolution.

You need to make decisions such as: What composition of components is effective for delivering

the functional requirements?

What composition of components allows for future change?

What will be the emergent properties of the composed

system?


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CBSE is a reuse-based approach to defining andimplementing loosely coupled components into systems.

A component is a software unit whose functionality anddependencies are completely defined by its interfaces.

A component model defines a set of standards that

component providers and composers should follow. During the CBSE process, the processes of requirements

engineering and system design are interleaved.


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25977233 Component Based Software Engineering

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