Attributes of Software Design, Key Features of Design

<< The Software Requirements Specification

Software Configuration Management Vs Software Maintenance >>

Software Project Management (CS615)

LECTURE # 16

2. Software Development Fundamentals

Technical Fundamentals

2.12

Design

⇒ Management Aspect

Major design styles

· Object, structured, data-structured design

Foundational design concepts

· Information hiding, abstraction, encapsulation, Inheritance, basic

algorithms & data structures, ...

⇒ Attributes of SW Design

Software design is actually a multi step process that focuses on four

distinct attributes of a program:

Data structure,

Software architecture,

Interface representations, and procedural (algorithmic) detail.

The design process translates requirements into a representation of the

software that can be assessed for quality before coding begins.

Like requirements, the design is documented and becomes part of the

software configuration.

Design is the technical kernel of software engineering. During design,

progressive refinements of data structure, architecture, interfaces, and

procedural detail of software components are developed, reviewed, and

documented.

Design results in representations of software that can be assessed for

quality. A number of fundamental software design principles and concepts

have been proposed over the past four decades.

Design principles guide the software engineer as the design process

proceeds. Design concepts provide basic criteria for design quality.

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Software Project Management (CS615)

a. Code generation

The design must be translated into a machine-readable form. The

code generation step performs this task. If design is performed in a

detailed manner, code generation can be accomplished

mechanistically.

b. Testing

Once code has been generated, program testing begins. The testing

process focuses on the logical internals of the software, ensuring

that all statements have been tested and on the functional externals;

that is, conducting tests to uncover errors and ensure that defined

input will produce actual results that agree with required results.

⇒ Key Features of Design

A number of fundamental software design principles and concepts have

been proposed over the past four decades. Design principles guide the

software engineer as the design process proceeds. Design concepts provide

basic criteria for design quality.

Support

Support

Software will undoubtedly undergo change after it is delivered to the

customer (a possible exception is embedded software). Change will occur

because errors have been encountered, because the software must be

adapted to accommodate changes in its external environment (e.g. a

change required because of a new operating system or peripheral device),

or because the customer requires functional or performance enhancements.

Software support/maintenance reapplies each of the preceding phases to

an existing program rather than a new one.

Modularity

Modularity (in both program and data) and the concept of abstraction

enable the designer to simplify and reuse software components.

Refinement provides a mechanism for representing successive layers of

functional detail. Program and data structure contribute to an overall view

of software architecture, while procedure provides the detail necessary for

algorithm implementation.

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Software Project Management (CS615)

Information hiding and functional independence provide heuristics for

achieving effective modularity.

We try to solve the problem by rushing through the design process so that

enough time will be left at the end of the project to uncover errors that

were made because we rushed through the design process.

The moral is this: Don't rush through it! Design is worth the effort.

⇒ Standard design approaches

Exception handling,

Localization

Portability

Reuse

Input/output

Memory management,

Performance

2.13

Construction

Coding practices

Naming, layout, documentation

Data-related concepts

Scope, persistence, binding time

Data usage guidelines

Bytes, arrays

Use of construction tools

Programming environment, group work support (documents, code),

code libraries & generators

2.14

Software Configuration management

Software configuration management (SCM) takes care of changes in a

software process. SCM identifies controls, audits, and reports

modifications that occur during software development. SCM helps

maintain the integrity of configurable items produced during software

development. SCM is an integral part of Software Quality Assurance

(SQA). SCM involves assessing the impact of the changes made during

SQA activities and making decisions based on cost and benefit analysis.

SCM is used to establish and maintain integrity of software items and

ensure that they can be traced easily. SCM helps define a library structure

for storage and retrieval of software items.

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Software Project Management (CS615)

To ensure that project stays consistent over time: You need to:

Evaluate proposed changes

Track the changes

Control the Version

Check integrity of Source code, documents, plans, design

Ensure quality

⇒ Software Configuration Management Activities

SCM is used to establish and maintain integrity of software items and

ensure that they can be traced easily. Using SCM, you can define a library

structure for storage and retrieval of software items. SCM needs to be

performed at all phases in the SDLC of a software project. The various

SCM activities are:

Identifying Objects

Controlling Versions

Controlling Changes

Auditing

Communicating Changes

1. Identifying Objects

The first activity in SCM involves identifying software configurable

items (SCIs). SCI is an aggregation of software that is designated for

configuration management. It is treated as a single entity in the

configuration management process. For example, design documents,

program code, test case, and custom requirement document are

configurable items.

You can use the Item Traceability Matrix to identify SCIs at the end of

each phase. A sample of Item Traceability Matrix is displayed in Table

1. In the table, you can see the different SCIs in different phases of the

development process.

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Software Project Management (CS615)

Table 1: Item Traceability Matrix

Phase

Deliverable

Requirement

Name

Design

Construction

Testing

Analysis

Requirement

Analysis

Analysis Document

Document

Functional

Specification

Design

Document and

Document

Program

Specification

Document

Code A

Code

Code B

Code C

Unit Test

Cases

Test Document

System Test

Cases

Database

Database Design

Design

Specification

Document

To identify SCls, you need to first breakdown the project deliverable

to the SCI level. Each phase in the project has its own deliverables. To

trace the deliverables, you need to map the SCls to the phases in which

they are delivered.

2. Controlling Versions

Version control combines procedures and tools to manage different

versions of configuration objects that are created during software

product development. To control versions, you can use Version

Control Register. In Version Control Register, you enter the details of

components, such as component identification numbers, their versions,

and dates of validity. It is advisable to release a baseline after a version

is released. Baseline is a specification or a product that is formally

reviewed and agreed upon. This serves as the basis for further

development. Baseline can be changed only through formal change

control procedures. A baseline consists of a set of SCIs that are

logically related to each other. Baselines are established when

subsequent changes to the SCIs need to be controlled. Version control

is essential so that everybody uses only the latest version. Any kind of

version mismatch might result in rework.

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