Transcript Chapter 5 Component-Based Development Process

Chapter 5
Component-Based Development Process
Building Reliable Component-based Systems
Chapter 5 - Component-Based Development Process
Page 1
Overview
 Software Process Models
 Component-based Development
 Component-Based Software Lifecycle
 Summary
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Purpose
 This chapter:

Describes the component-based software lifecycle.

Provides an overview of generic software engineering
processes.

Motivates the need for specific processes when
developing components and when building systems or
applications 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 requirements
and 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 Incremental Model
Increment 1 2...n
Analysis
Design
Implementation
Integration
Test
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The Prototyping Model
Test prototype
Analysis
Design
Develop
prototype
Implementation
Integration
Test
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Unified Process
 Inception

The first phase in which the system is described in a
formalized way, providing a base for further
development.
 Elaboration

The phase in which the system architecture is defined
and created.
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Unified Process continued
 Construction

The development of completely new products, with
reuse capabilities.
 Transition

The work of delivering the product to the customer.
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Unified Process Illustrated
Phases
Inception
Elaboration
Construction
Transition
Requirements
An iteration in the
elaboration phase
Analysis
Design
Implementation
Test
Iter #1
Iter #2
---
---
---
---
---
---
Iter #n
Iterations
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Component-based Development
 Reuse Approach
 Separation of Development Processes
 Component-based Development (CBD) – The Consumer
Perspective
 Component Development (CD) – The Producer
Perspective
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Reuse Approach
 The reuse approach makes the following assumptions:

All experience can be reused.

Reuse typically requires some modification of objects
being reused.

Reuse must be integrated into the specific software
development.

Analysis is necessary to determine when, and if, reuse
is appropriate.
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Reuse
 For given requirements r for an object x, we propose the
reuse of the already existing object xk. The reuse
procedure includes:

Identification of a set of objects x1 , x2 … xm as
candidates,

Selection of one of these, and, if required,

Its modification to translate xk to x’ which is as close to x
as 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 and
relations between them, beginning from the system
requirements and from the availability of components
already existing.
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Component Guidelines
 Components are built to be used and reused in many
applications 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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CBD – The Consumer Perspective
 Typically a component consumer selects a component
and then uses it in a software system.
 The component lifecycle must be considered in relation
to 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 new
component 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 versions
of the surrounding systems and applications?
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CD – The Producer Perspective
 The producer of a component must take into
consideration:

The business goal

Component functionality

Maintenance policy

The type of application and system in which the
component 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 and
systems are not necessarily compatible.

The component’s maintenance requirements should be
synchronous with those of the system in which they are
to be incorporated.
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Disposal
 Disposal of Component-based Systems generally takes
place 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 the
system 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 producer
ceases 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 or
maintenance.
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Disposal: Considerations
 Both producer and consumer should arrive at a
compromise with respect to the lifecycles of their
different 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-existing
components, rather than on the implementation of the
system designed.
 First

Find reusable units which will meet the requirements
specified and will be compliant with the system design.
 Second

Determine the amount of extra effort required to use
reusable units instead of units dedicated to a particular
purpose.
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Requirements Analysis and Definition
 The three analysis tasks:

Capture the system requirements and define the system
boundaries.

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 find
components
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Analysis and Definition Continued
 Not finding a component which exactly satisfies the
requirements necessitates the development of a new
component.
 The process of design and even requirements
engineering will be combined with component selection
and 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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Technical and Non-technical Evaluation
 Technical aspects of evaluation include

Integration

Validation

Verification
 Examples of non-technical issues include:

The marketing position of the component supplier

Maintenance support provided

Alternative solutions, etc
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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 of
candidate components.
5.
If necessary refine the requirements, and repeat the
evaluation 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 an
external component.
 Criteria which may favor the selection of an external
component :

Time-to-market

Production and maintenance costs,

Quality
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Evaluation of the Assembly
 It is necessary to evaluate the assembly; evaluation of
the individual components is not sufficient.

This implies that an investigation of the integration
procedure may be a part of an evaluation.
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System Design
 System specification and definition of the system
architecture

The initial architecture will be a result of both the overall
requirements and the choice of component model.

Many decisions related to the system design will be a
consequence 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 combinations
of these.
 Evolutionary approach:

To find the most appropriate and feasible combination of
the component candidates. In this way the results of the
design activity may be less predictable.
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System Implementation
 Implementation by coding can be reduced to the
creation of the “glue-code” and to component
adaptation.

This effort is usually less than 50% of the total
development effort.

Effort per line of glue-code is about three times the effort
per line of the application’s code.
 It may still be necessary to design and implement some
components.
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System Integration
 Integration

Is the composition of the implemented and selected
components 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 system
requirements.
 Reconfigurations of assemblies

Different assemblies (or composite components) can
include common basic components. for re-configuring
assemblies must exist.
 Emerging properties

An important fact is that it is not possible to discover all
the effects of a component until the integration is
performed.
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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 to
check that it functions in accordance with its
specification.

We should also note that the component validation is
strongly related to system validation.
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System Verification and Validation
 System verification and validation process is similar to
the processes for non-component-based systems.
 The difference is that the implications of the processes
may be different – new component requirements may
emerge and it may happen that the selected
components cannot meet the new requirements.
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System Operation Support and Maintenance
 Components exist even at run-time, making it possible
to:

Improve and maintain the system by updating or adding
new 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 it
is not necessarily clear who:

Is supporting the system.

The system vendor is.

The component vendors are.
 Components can be used by several other components
introducing 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 B
Version V1
Product P
Version V2
Component A
Version V2
Component B
Version V2
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System Development Process
 Consists of parallel tracks in which:

The basic architecture and its environment is being
developed and managed concurrently with both the
development of applications consisting of components
and the evaluation of the actual components.
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Component-based Development Process
Analysis
Find
Design
Select
Implementation
Adapt
Integration
Integrate
Test
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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Requirements Analysis and Definition
 The development of reusable components would be
easier if requirements remained constant during the
time of component and system development.

As a result of new requirements for the systems old or
new requirements for the components will emerge.

The more reusable a component is, the more demands
are placed on it.
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Accumulated Component Requirements
Accumulated Requirements
Component
Product P1
Product P2
t-0
t-1
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Designing for Reusability
 For a component to be reusable, it must be designed in
a more general way than a component tailored for a
unique situation.
 Components intended to be reused requires
adaptability. This will increase the size and complexity
of the components
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Component Specification
 It is important that the component be clearly and
properly specified.
 The consumer must be able to understand the
component specification.
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Summary
 In a component-based development process we
distinguish development of components from
development of systems using components:

Component development process: Is focused on
building reusable units.

System development process: Concentrates on the
reuse of components, their evaluation and integration.
 These processes are often performed independently of
each other.
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Summary Continued
 To achieve a proper balance between the independence
of and collaboration between the processes remains a
challenge for researchers and practitioners
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