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Page 1Building Reliable Component-based SystemsChapter 5 - Component-Based Development Process

Chapter 5

Component-Based Development Process

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Purpose

This chapter:

Describes the component-based software lifecycle.

Provides an overview of generic software engineeringprocesses.

Motivates the need for specific processes whendeveloping components and when building systems orapplications from components

Describe these processes, reviewing their procedures.

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Software Process Models

Generic lifecycle activities

The Sequential Model

Evolutionary Development

Unified Process

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Generic lifecycle activities

Activities

Requirements analysis and system specification

System and software design

Implementation and unit testing Integration, system verification and validation

Operation support and Maintenance

Disposal

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The Sequential Model

Analysis

Design

Implementation

Integration

Test

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Evolutionary Development

Develop a system gradually in many repetitive stages:

Increasing the knowledge of the system requirementsand system functionality in each stage

exposing the results to user comments.

This can be achieved by using:

The Iterative Model

The Incremental Model

The Prototyping Model

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The Iterative Model

Analysis

Design

Implementation

Integration

Test

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The Prototyping Model

Analysis

Design

Implementation

Integration

Test

Develop

prototype

Test prototype

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Unified Process

Inception

The first phase in which the system is described in aformalized way, providing a base for furtherdevelopment.

Elaboration

The phase in which the system architecture is definedand created.

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Unified Process continued

Construction

The development of completely new products, withreuse capabilities.

Transition

The work of delivering the product to the customer.

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Unified Process Illustrated

Inception Elaboration Construction Transition

Requirements

Analysis

Design

Implementation

Test

Iter #1 Iter #nIter #2 --- --- --- --- --- ---

An iteration in the

elaboration phase

Phases

Iterations

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Component-based Development

Reuse Approach

Separation of Development Processes

Component-based Development (CBD) The ConsumerPerspective

Component Development (CD) The ProducerPerspective

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Reuse

For given requirements rfor an object x, we propose thereuse of the already existing object x

k. The reuse

procedure includes:

Identification of a set of objectsx1 ,x2 xm as

candidates, Selection of one of these, and, if required,

Its modification to translatexktox which is as close toxas possible.

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Reuse continued

The object x can be of any type:

A system architecture

An overall design

A design pattern

An infrastructure

Different types of components or services.

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Separation of Development Processes

Component development

System development with components

System development with components

Focuses on the identification of reusable entities andrelations between them, beginning from the systemrequirements and from the availability of componentsalready existing.

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Component Guidelines

Components are built to be used and reused in manyapplications and should thus be:

Well specified

Easy to understand

Sufficiently general

Easy to adapt

Easy to deliver and deploy

Easy to replace

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CBDThe Consumer Perspective

Typically a component consumer selects a componentand then uses it in a software system.

The component lifecycle must be considered in relationto the lifecycle of the system as a whole.

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The Consumer Perspective Continued

Common considerations:

Will the component producer be able to deliver a newcomponent version when this is required?

How will changes in a component in the system affect

the behavior of another component?

Will the component be compatible with newer versionsof the surrounding systems and applications?

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CDThe Producer Perspective

The producer of a component must take intoconsideration:

The business goal

Component functionality

Maintenance policy

The type of application and system in which thecomponent will be used

The requirements of the system

The life expectancy of relevant systems

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Additional Considerations

The maintenance requirements of components andsystems are not necessarily compatible.

The components maintenance requirements should besynchronous with those of the system in which they are

to be incorporated.

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Disposal

Disposal of Component-based Systems generally takesplace due to two different factors:

Dissatisfaction

Obsolescence

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Disposal: Dissatisfaction

Initiated by consumers when they conclude that:

The component no longer provides the support of thesystem it was intended to provide or;

That the system no longer needs the component.

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Disposal: Obsolescence

When a component becomes obsolete and the producerceases component maintenance and operation support.

This is likely to occur when:

A new, more effective component with the same, similar

or extended functionality is found.

The producer is not able to continue with support ormaintenance.

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Disposal: Considerations

Both producer and consumer should arrive at acompromise with respect to the lifecycles of theirdifferent products.

The consumer should always have in mind an

alternative solution, such as: The replacement of the component with another

developed internally or by another producers.

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Component-Based Software Lifecycle

Development With Components

Requirements Analysis and Definition

Component Selection and Evaluation

System Design

System Implementation

System Integration

Verification and Validation

System Operation Support and Maintenance

System Development Process

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Development With Components

Emphasis is placed on the reuse of pre-existingcomponents, rather than on the implementation of thesystem designed.

First

Find reusable units which will meet the requirementsspecified and will be compliant with the system design.

Second

Determine the amount of extra effort required to usereusable units instead of units dedicated to a particularpurpose.

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The three analysis tasks:

Capture the system requirements and define the systemboundaries.

Define the system architecture to permit component

collaboration. Define component requirements to permit the selection

or development of the required components.

The approach is:

optimistic and an idealized view of the process. It assumes that the component requirements can be

precisely defined and that it is possible to findcomponents

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Analysis and Definition Continued

Not finding a component which exact lysatisfies therequirements necessitates the development of a newcomponent.

The process of design and even requirements

engineering will be combined with component selectionand the evaluation process.

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Component Selection and Evaluation

The components selected must therefore be evaluated:

Technically

Non-technically

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Evaluation Methods

Procurement-oriented requirements engineering:

1. Identify several component candidates.

2. Investigate these.

3. Reject those not compliant with the main requirements.

4. Continue with the evaluation of the reduced number ofcandidate components.

5. If necessary refine the requirements, and repeat theevaluation process.

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Evaluation Methods Continued

One scenario is to:

1. Search for an internally developed component.

2. If none suitable is found, continue by searching for anexternal component.

Criteria which may favor the selection of an externalcomponent :

Time-to-market

Production and maintenance costs,

Quality

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Evaluation of the Assembly

It is necessary to evaluate the assembly; evaluation ofthe individual components is not sufficient.

This implies that an investigation of the integrationprocedure may be a part of an evaluation.

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System Design

System specification and definition of the systemarchitecture

The initial architecture will be a result of both the overallrequirements and the choice of component model.

Many decisions related to the system design will be aconsequence of the component model selected.

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System Design: Evolutionary Approach

Component selection procedure:

Selection of component candidates, followed by;

Consideration of the feasibility of different combinationsof these.

Evolutionary approach:

To find the most appropriate and feasible combination ofthe component candidates. In this way the results of thedesign activity may be less predictable.

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System Implementation

Implementation by coding can be reduced to thecreation of the glue-code and to componentadaptation.

This effort is usually less than 50% of the totaldevelopment effort.

Effort per line of glue-code is about three times the effortper line of the applications code.

It may still be necessary to design and implement somecomponents.

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System Integration

Integration

Is the composition of the implemented and selectedcomponents to constitute the software system.

There are several other aspects to be taken into

consideration, namely: Component adaptation;

Reconfigurations of assemblies;

Emerging properties of assemblies integrated into the

system.

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Integration Considerations

Component adaptation

In many cases a component must be adjusted to systemrequirements.

Reconfigurations of assemblies

Different assemblies (or composite components) caninclude common basic components. for re-configuringassemblies must exist.

Emerging properties

An important fact is that it is not possible to discover allthe effects of a component until the integration isperformed.

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Verification and Validation

Expressed by Boehm

Validation: are we building the right product ?

Verification: Are we building the product right ?

Component Validation and Verification

After a component is selected it should be tested tocheck that it functions in accordance with itsspecification.

We should also note that the component validation is

strongly related to system validation.

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Page 43Building Reliable Component-based Systems

Chapter 5 - Component-Based Development Process

System Verification and Validation

System verification and validation process is similar tothe processes for non-component-based systems.

The difference is that the implications of the processesmay be differentnew component requirements mayemerge and it may happen that the selectedcomponents cannot meet the new requirements.

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System Operation Support and Maintenance

Components exist even at run-time, making it possibleto:

Improve and maintain the system by updating or addingnew components to the system.

Improve the system quicker and more flexibly.

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Operation and Support: Considerations

Maintenance procedures can be more complicated as itis not necessarily clear who:

Is supporting the system.

The system vendor is.

The component vendors are.

Components can be used by several other componentsintroducing version incompatibilities.

The same problem may appear when we install a

component package.

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Inconsistent Component Integration

Product P

Version V1

Component A

Version V1

Component A

Version V2

Component B

Version V1 Component BVersion V2

Product P

Version V2

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System Development Process

Consists of parallel tracks in which:

The basic architecture and its environment is beingdeveloped and managed concurrently with both thedevelopment of applications consisting of componentsand the evaluation of the actual components.

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Component-based Development Process

Analysis

Design

Implementation

Integration

Test

Find

Select

Adapt

Integrate

Test

Component evaluation System Development

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Component Development

Requirements must be

captured

analyzed

defined

The component must be

designed

implemented

verified validated

delivered

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Component Development Considerations

Components are built to be part of something else,thus:

There is greater difficulty in managing requirements;

Greater efforts are needed to develop reusable units;

A precise component specification is required

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The development of reusable components would beeasier if requirements remained constant during thetime of component and system development.

As a result of new requirements for the systems old ornew requirements for the components will emerge.

The more reusable a component is, the more demandsare placed on it.

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Accumulated Component Requirements

Product P2

Product P1

Component

Accumulated Requirements

t-0 t-1

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Building Reliable Component-based Systems


Designing for Reusability

For a component to be reusable, it must be designed ina more general way than a component tailored for aunique situation.

Components intended to be reused requiresadaptability. This will increase the size and complexityof the components

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Component Specification

It is important that the component be clearly andproperly specified.

The consumer must be able to understand thecomponent specification.

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Summary

In a component-based development process wedistinguish development of components fromdevelopment of systems using components:

Component development process: Is focused onbuilding reusable units.

System development process: Concentrates on thereuse of components, their evaluation and integration.

These processes are often performed independently ofeach other.

S C i d

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Building Reliable Component based Systems

Summary Continued

To achieve a proper balance between the independenceof and collaboration between the processes remains achallenge for researchers and practitioners

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