Software Engineering

Chanderprabhu Jain College of Higher Studies & School of Law
Plot No. OCF, Sector A-8, Narela, New Delhi – 110040
(Affiliated to Guru Gobind Singh Indraprastha University and Approved by Govt of NCT of Delhi & Bar Council of India)
Semester: Second Semester
Subject Code:110
Name of the Subject:
SOFTWARE ENGINEERING

Software crisis
Software crisis is a term used in the early days of
computing science for the difficulty of writing useful and
efficient computer programs in the required time. The
software crisis was due to the rapid increases in
computer power and the complexity of the problems that
could not be tackled. With the increase in the complexity
of the software, many software problems arose because
existing methods were insufficient.
The term "software crisis" was coined by some
attendees at the first NATO Software Engineering
Conference in 1968 at Garnish, Germany.

The causes of the software crisis were linked to the
overall complexity of hardware and the software
development process. The crisis manifested itself in
several ways:
• Projects running over-budget
• Projects running over-time
• Software was very inefficient
• Software was of low quality
• Software often did not meet requirements
• Projects were unmanageable and code difficult to
maintain
• Software was never delivered

Software Engineering
Software engineering is an engineering branch associated with
development of software product using well-defined scientific principles,
methods and procedures. The outcome of software engineering is an
efficient and reliable software product.
Software project management has wider scope than software
engineering process as it involves communication, pre and post delivery
support etc.
This tutorial should provide you basic understanding of software
product, software design and development process, software project
management and design complexities etc. At the end of the tutorial you
should be equipped with well understanding of software engineering
concepts.

SDLC Activities
SDLC provides a series of steps to be followed to design and develop a software
product efficiently. SDLC framework includes the following steps:

Communication
This is the first step where the user initiates the
request for a desired software product. He
contacts the service provider and tries to
negotiate the terms. He submits his request to
the service providing organization in writing.

Feasibility Study
After requirement gathering, the team comes up
with a rough plan of software process. At this step
the team analyzes if a software can be made to fulfill
all requirements of the user and if there is any
possibility of software being no more useful. It is
found out, if the project is financially, practically and
technologically feasible for the organization to take
up. There are many algorithms available, which help
the developers to conclude the feasibility of a
software project.

System Analysis
At this step the developers decide a roadmap of their plan and
try to bring up the best software model suitable for the project.
System analysis includes Understanding of software product
limitations, learning system related problems or changes to be
done in existing systems beforehand, identifying and
addressing the impact of project on organization and
personnel etc. The project team analyzes the scope of the
project and plans the schedule and resources accordingly.

Software Design
Next step is to bring down whole knowledge of requirements and
analysis on the desk and design the software product. The inputs from
users and information gathered in requirement gathering phase are the
inputs of this step. The output of this step comes in the form of two
designs; logical design and physical design. Engineers produce meta-
data and data dictionaries, logical diagrams, data-flow diagrams and in
some cases pseudo codes.
Coding
This step is also known as programming phase. The implementation of
software design starts in terms of writing program code in the suitable
programming language and developing error-free executable programs
efficiently.

Software quality
In the context of software engineering, software quality refers to two
related but distinct notions that exist wherever quality is defined in a
business context:
Software functional quality reflects how well it complies with or
conforms to a given design, based on functional requirements or
specifications. That attribute can also be described as the fitness for
purpose of a piece of software or how it compares to competitors in the
marketplace as a worthwhile product. It is the degree to which the
correct software was produced.
Software structural quality refers to how it meets non-functional
requirements that support the delivery of the functional requirements,
such as robustness or maintainability. It has a lot more to do with the
degree to which the software works as needed.

Testing and Quality Assurance
The software system needs to be checked for its intended behavior and
direction of progress at each development stage to avoid duplication of
efforts, time and cost overruns, and to assure completion of the system
within stipulated time.The software system needs to be checked for its
intended behavior and direction of progress at each development stage to
avoid duplication of efforts, time and cost overruns, and to assure
completion of the system within stipulated time.
System testing and quality assurance come to aid for checking the system.
It includes −
• Product level quality (Testing)
• Process level quality.

Testing
Testing is the process or activity that checks the functionality
and correctness of software according to specified user
requirements in order to improve the quality and reliability of
system. It is an expensive, time consuming, and critical
approach in system development which requires proper
planning of overall testing process.
A successful test is one that finds the errors. It executes the
program with explicit intention of finding error, i.e., making
the program fail. It is a process of evaluating system with an
intention of creating a strong system and mainly focuses on
the weak areas of the system or software.

Characteristics of System Testing
System testing begins at the module level and proceeds towards the integration
of the entire software system. Different testing techniques are used at different
times while testing the system. It is conducted by the developer for small projects
and by independent testing groups for large projects.
Test Strategy
It is a statement that provides information about the various levels, methods,
tools, and techniques used for testing the system. It should satisfy all the
needs of an organization.
Test Plan
• It provides a plan for testing the system and verifies that the system under
testing fulfils all the design and functional specifications. The test plan
provides the following information −
• Objectives of each test phase
• Approaches and tools used for testing
• Responsibilities and time required for each testing activity
• Availability of tools, facilities, and test libraries
• Procedures and standards required for planning and conducting the tests
• Factors responsible for successful completion of testing process

Quality Assurance
• It is the review of system or software products and its documentation
for assurance that system meets the requirements and specifications.
• Purpose of QA is to provide confidence to the customers by constant
delivery of product according to specification.
• Software quality Assurance (SQA) is a techniques that includes
procedures and tools applied by the software professionals to ensure
that software meet the specified standard for its intended use and
performance.
• The main aim of SQA is to provide proper and accurate visibility of
software project and its developed product to the administration.
• It reviews and audits the software product and its activities throughout
the life cycle of system development.

Objectives of Quality Assurance
The objectives of conducting quality assurance are as follows −
• To monitor the software development process and the final software
developed.
• To ensure whether the software project is implementing the standards and
procedures set by the management.
• To notify groups and individuals about the SQA activities and results of
these activities.
• To ensure that the issues, which are not solved within the software are
addressed by the upper management.
• To identify deficiencies in the product, process, or the standards, and fix
them.

Requirements analysis
In systems engineering and software engineering, requirements
analysis encompasses those tasks that go into determining the needs
or conditions to meet for a new or altered product or project, taking
account of the possibly conflicting requirements of the various
stakeholders, analyzing, documenting, validating and managing
software or system requirements.
Requirements analysis is critical to the success or failure of a systems
or software project. The requirements should be documented,
actionable, measurable, testable, traceable, related to identified
business needs or opportunities, and defined to a level of detail
sufficient for system design.

Software prototyping
Software prototyping is the activity of creating prototypes of software
applications, i.e., incomplete versions of the software program being developed.
It is an activity that can occur in software development and is comparable to
prototyping as known from other fields, such as mechanical engineering or
manufacturing.
A prototype typically simulates only a few aspects of, and may be completely
different from, the final product.
Prototyping has several benefits: the software designer and implementer can
get valuable feedback from the users early in the project. The client and the
contractor can compare if the software made matches the software
specification, according to which the software program is built. It also allows the
software engineer some insight into the accuracy of initial project estimates and
whether the deadlines and milestones proposed can be successfully met. The
degree of completeness and the techniques used in prototyping have been in
development and debate since its proposal in the early 1970s.

Software requirements specification
A software requirements specification (SRS) is a description of a
software system to be developed. It is modeled after business
requirements specification (CONOPS), also known as a stakeholder
requirements specification (StRS). The software requirements
specification lays out functional and non-functional requirements, and it
may include a set of use cases that describe user interactions that the
software must provide.

Elements of the analysis model
1. Scenario based element
• This type of element represents the system user point of view.
• Scenario based elements are use case diagram, user stories.
2. Class based elements
• The object of this type of element manipulated by the system.
• It defines the object,attributes and relationship.
• The collaboration is occurring between the classes.
• Class based elements are the class diagram, collaboration diagram.
3. Behavioral elements
• Behavioral elements represent state of the system and how it is changed by the
external events.
• The behavioral elements are sequenced diagram, state diagram.
4. Flow oriented elements
• An information flows through a computer-based system it gets transformed.
• It shows how the data objects are transformed while they flow between the
various system functions.
• The flow elements are data flow diagram, control flow diagram.

Concepts of data modeling
Analysis modeling starts with the data modeling.
The software engineer defines all the data object that proceeds within the
system and the relationship between data objects are identified.
Data objects
The data object is the representation of composite information.
The composite information means an object has a number of different
properties or attribute.
For example, Height is a single value so it is not a valid data object, but
dimensions contain the height, the width and depth these are defined as
an object.

Structured analysis
In software engineering, structured analysis (SA) and
structured design (SD) are methods for analyzing
business requirements and developing specifications for
converting practices into computer programs, hardware
configurations, and related manual procedures.
Structured analysis and design techniques are fundamental
tools of systems analysis. They developed from classical
systems analysis of the 1960s and 1970s.

Data dictionary
Entity relationship diagram, essential for the design of database tables, extracts,
and metadata.
A data dictionary or database dictionary is a file that defines the basic organization
of a database. A database dictionary contains a list of all files in the database, the
number of records in each file, and the names and types of each data field. Most
database management systems keep the data dictionary hidden from users to
prevent them from accidentally destroying its contents. Data dictionaries do not
contain any actual data from the database, only bookkeeping information for
managing it. Without a data dictionary, however, a database management system
cannot access data from the database.

Software engineering
Software engineering is an engineering branch associated
with development of software product using well-defined
scientific principles, methods and procedures. The outcome
of software engineering is an efficient and reliable software
product.
Software project management has wider scope than software
engineering process as it involves communication, pre and
post delivery support etc.

Software design
Software design is a process to transform user requirements
into some suitable form, which helps the programmer in
software coding and implementation.
For assessing user requirements, an SRS (Software
Requirement Specification) document is created whereas for
coding and implementation, there is a need of more specific
and detailed requirements in software terms. The output of
this process can directly be used into implementation in
programming languages.

Some of the commonly followed design principles are as following.
Software design should correspond to the analysis model: Often a design
element corresponds to many requirements, therefore, we must know how the
design model satisfies all the requirements represented by the analysis model.
Choose the right programming paradigm: A programming paradigm describes
the structure of the software system.
Software design should be uniform and integrated: Software design is
considered uniform and integrated, if the interfaces are properly defined among the
design components.
Software design should be flexible: Software design should be flexible enough
to adapt changes easily. To achieve the flexibility, the basic design concepts such
as abstraction, refinement, and modularity should be applied effectively.
Software design should ensure minimal conceptual (semantic) errors: The
design team must ensure that major conceptual errors of design such as
ambiguousness and inconsistency are addressed in advance before dealing with
the syntactical errors present in the design model.

Software Design Concepts
Every software process is characterized by basic concepts
along with certain practices or methods. Methods represent
the manner through which the concepts are applied. As new
technology replaces older technology, many changes occur
in the methods that are used to apply the concepts for the
development of software. However, the fundamental
concepts underlining the software design process remain the
same, some of which are described here.

Abstraction
Abstraction refers to a powerful design tool, which allows
software designers to consider components at an abstract
level, while neglecting the implementation details of the
components. IEEE defines abstraction as 'a view of a
problem that extracts the essential information relevant to a
particular purpose and ignores the remainder of the
information.' The concept of abstraction can be used in two
ways: as a process and as an entity. As a process, it refers
to a mechanism of hiding irrelevant details and
representing only the essential features of an item so that
one can focus on important things at a time. As an entity, it
refers to a model or view of an item.

Software Design
Strategies
Software design is a process to conceptualize the software
requirements into software implementation. Software design takes the
user requirements as challenges and tries to find optimum solution.
While the software is being conceptualized, a plan is chalked out to
find the best possible design for implementing the intended solution.

Software Design
Strategies
Software design is a process to conceptualize the software requirements
into software implementation. Software design takes the user
requirements as challenges and tries to find optimum solution. While the
software is being conceptualized, a plan is chalked out to find the best
possible design for implementing the intended solution.

Object Oriented Design
Object oriented design works around the entities and their
characteristics instead of functions involved in the software system. This
design strategies focuses on entities and its characteristics. The whole
concept of software solution revolves around the engaged entities.
Let us see the important concepts of Object Oriented Design:
Objects - All entities involved in the solution design are known as
objects. For example, person, banks, company and customers are
treated as objects. Every entity has some attributes associated to it and
has some methods to perform on the attributes.
Classes - A class is a generalized description of an object. An object is
an instance of a class. Class defines all the attributes, which an object
can have and methods, which defines the functionality of the object.

Software Design Approaches
Here are two generic approaches for software designing:
Top Down Design
We know that a system is composed of more than one sub-
systems and it contains a number of components. Further,
these sub-systems and components may have their on set of
sub-system and components and creates hierarchical
structure in the system. Bottom-up Design
The bottom up design model starts with most specific and
basic components. It proceeds with composing higher level
of components by using basic or lower level components. It
keeps creating higher level components until the desired
system is not evolved as one single component. With each
higher level, the amount of abstraction is increased.

Functional testing is a Functional testing
quality assurance (QA) process and a type of black-box
testing that bases its test cases on the specifications of the
software component under test. Functions are tested by
feeding them input and examining the output, and internal
program structure is rarely considered (unlike white-box
testing). Functional testing usually describes what the system
does.
Functional testing does not imply that you are testing a
function (method) of your module or class. Functional testing
tests a slice of functionality of the whole system.
Functional testing

• Smoke testing
• Sanity testing
• Regression testing
• Usability testing
Functional testing has many types:

What is Structural Testing ?
Structural testing, also known as glass box testing or white box
testing is an approach where the tests are derived from the
knowledge of the software's structure or internal implementation.
The other names of structural testing includes clear box testing,
open box testing, logic driven testing or path driven testing. The
other names of structural testing includes clear box testing, open
box testing, logic driven testing or path driven testing.

Structural Testing Techniques:
Statement Coverage - This technique is aimed at exercising all programming
statements with minimal tests.
Branch Coverage - This technique is running a series of tests to ensure that
all branches are tested at least once.
Path Coverage - This technique corresponds to testing all possible paths
which means that each statement and branch are covered.
Calculating Structural Testing Effectiveness:
Statement Testing = (Number of Statements Exercised / Total Number of
Statements) x 100 %
Branch Testing = (Number of decisions outcomes tested / Total Number of
decision Outcomes) x 100 %
Path Coverage = (Number paths exercised / Total Number of paths in the
program) x 100 %

What is Debugging?
It is a systematic process of spotting and fixing the number of bugs, or defects, in
a piece of software so that the software is behaving as expected. Debugging is
harder for complex systems in particular when various subsystems are tightly
coupled as changes in one system or interface may cause bugs to emerge in
another.
Debugging is a developer activity and effective debugging is very important before
testing begins to increase the quality of the system. Debugging will not give
confidence that the system meets its requirements completely but testing gives
confidence.

Software Maintenance Overview
Software maintenance is widely accepted part of SDLC now a days. It stands for
all the modifications and updations done after the delivery of software product.
There are number of reasons, why modifications are required, some of them are
briefly mentioned below:
Market Conditions - Policies, which changes over the time, such as taxation
and newly introduced constraints like, how to maintain bookkeeping, may trigger
need for modification.
Client Requirements - Over the time, customer may ask for new features or
functions in the software.
Host Modifications - If any of the hardware and/or platform (such as operating
system) of the target host changes, software changes are needed to keep
adaptability.
Organization Changes - If there is any business level change at client end,
such as reduction of organization strength, acquiring another company,
organization venturing into new business, need to modify in the original software
may arise.

Types of maintenance
In a software lifetime, type of maintenance may vary based on its nature. It
may be just a routine maintenance tasks as some bug discovered by some
user or it may be a large event in itself based on maintenance size or nature.
Following are some types of maintenance based on their characteristics:
Corrective Maintenance - This includes modifications and updations done in
order to correct or fix problems, which are either discovered by user or
concluded by user error reports.
Adaptive Maintenance - This includes modifications and updations applied
to keep the software product up-to date and tuned to the ever changing world
of technology and business environment.
Perfective Maintenance - This includes modifications and updates done in
order to keep the software usable over long period of time
Preventive Maintenance - This includes modifications and updations to
prevent future problems of the software. It aims to attend problems, which are
not significant at this moment but may cause serious issues in future.

Cost of Maintenance
Reports suggest that the cost of maintenance is high. A study on estimating
software maintenance found that the cost of maintenance is as high as 67% of
the cost of entire software process cycle.

Maintenance Activities
IEEE provides a framework for sequential maintenance process activities. It can
be used in iterative manner and can be extended so that customized items and
processes can be included.

Software Re-engineering
When we need to update the software to keep it to the current market, without
impacting its functionality, it is called software re-engineering. It is a thorough
process where the design of software is changed and programs are re-written.
Legacy software cannot keep tuning with the latest technology available in the
market. As the hardware become obsolete, updating of software becomes a
headache. Even if software grows old with time, its functionality does not.
For example, initially Unix was developed in assembly language. When
language C came into existence, Unix was re-engineered in C, because
working in assembly language was difficult.

Reverse Engineering
It is a process to achieve system specification by thoroughly analyzing,
understanding the existing system. This process can be seen as reverse SDLC
model, i.e. we try to get higher abstraction level by analyzing lower abstraction
levels.
An existing system is previously implemented design, about which we know
nothing. Designers then do reverse engineering by looking at the code and try to
get the design. With design in hand, they try to conclude the specifications. Thus,
going in reverse from code to system specification.

Program Restructuring
It is a process to re-structure and re-construct the existing software. It is all
about re-arranging the source code, either in same programming language or
from one programming language to a different one. Restructuring can have
either source code-restructuring and data-restructuring or both.
Re-structuring does not impact the functionality of the software but enhance
reliability and maintainability. Program components, which cause errors very
frequently can be changed, or updated with re-structuring.
The dependability of software on obsolete hardware platform can be removed
via re-structuring.

Forward Engineering
Forward engineering is a process of obtaining desired software from the
specifications in hand which were brought down by means of reverse
engineering. It assumes that there was some software engineering already
done in the past.
Forward engineering is same as software engineering process with only one
difference – it is carried out always after reverse engineering.

Software configuration
management
In software engineering, software configuration management (SCM or
S/W CM) is the task of tracking and controlling changes in the software, part
of the larger cross-disciplinary field of configuration management. SCM
practices include revision control and the establishment of baselines. If
something goes wrong, SCM can determine what was changed and who
changed it. If a configuration is working well, SCM can determine how to
replicate it across many hosts.
The acronym "SCM" is also expanded as source configuration
management process and software change and configuration
management. However, "configuration" is generally understood to cover
changes typically made by a system administrator.

Software Engineering

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