Lecture1422914635

VEER SURENDRA SAI UNIVERSITY OF TECHNOLOGY
BURLA – 768018
Lecture Notes on Software Engineering
By
Dr. H.S.Behera
Asst. Prof. K.K.Sahu
Asst. Prof. Gargi Bhattacharjee

CONTENTS
Module: 1
Lecture 1: Introduction to Software Engineering
Lecture 2: Software Development Life Cycle, Classical Waterfall Model, Iterative Model
Lecture 3: Prototype Model, Spiral Model
Lecture 4: Requirement Analysis & Specification
Lecture 5: Software Requirement Characteristics, User Interface Requirements
Lecture 6: Software Design
Lecture 7: Cohesion & Coupling
Lecture 8: Software Analysis & Design Tools – DFD
Lecture 9: Structure Charts, Structured English
Lecture 10: Decision Table, ER Model, Data Dictionary
REFERENCES

MODULE 1
LECTURE NOTE-1
INTRODUCTION TO SOFTWARE ENGINEERING
The term software engineering is composed of two words, software and engineering.
Software is more than just a program code. A program is an executable code, which serves
some computational purpose. Software is considered to be a collection of executable
programming code, associated libraries and documentations. Software, when made for a
specific requirement is called software product.
Engineering on the other hand, is all about developing products, using well-defined, scientific
principles and methods.
So, we can define software engineering as an engineering branch associated with the
development of software product using well-defined scientific principles, methods and
procedures. The outcome of software engineering is an efficient and reliable software product.
IEEE defines software engineering as:
The application of a systematic, disciplined, quantifiable approach to the development,
operation and maintenance of software.
We can alternatively view it as a systematic collection of past experience. The experience is
arranged in the form of methodologies and guidelines. A small program can be written without
using software engineering principles. But if one wants to develop a large software product, then
software engineering principles are absolutely necessary to achieve a good quality software cost
effectively.
Without using software engineering principles it would be difficult to develop large programs. In
industry it is usually needed to develop large programs to accommodate multiple functions. A
problem with developing such large commercial programs is that the complexity and difficulty
levels of the programs increase exponentially with their sizes. Software engineering helps to
reduce this programming complexity. Software engineering principles use two important
techniques to reduce problem complexity: abstraction and decomposition. The principle of
abstraction implies that a problem can be simplified by omitting irrelevant details. In other
words, the main purpose of abstraction is to consider only those aspects of the problem that are
relevant for certain purpose and suppress other aspects that are not relevant for the given
purpose. Once the simpler problem is solved, then the omitted details can be taken into

consideration to solve the next lower level abstraction, and so on. Abstraction is a powerful way
of reducing the complexity of the problem. The other approach to tackle problem complexity is
decomposition. In this technique, a complex problem is divided into several smaller problems
and then the smaller problems are solved one by one. However, in this technique any random
decomposition of a problem into smaller parts will not help. The problem has to be decomposed
such that each component of the decomposed problem can be solved independently and then the
solution of the different components can be combined to get the full solution. A good
decomposition of a problem should minimize interactions among various components. If the
different subcomponents are interrelated, then the different components cannot be solved
separately and the desired reduction in complexity will not be realized.
NEEDOFSOFTWAREENGINEERING
The need of software engineering arises because of higher rate of change in user requirements
and environment on which the software is working.
 Large software - It is easier to build a wall than to a house or building, likewise, as the
size of software become large engineering has to step to give it a scientific process.
 Scalability- If the software process were not based on scientific and engineering
concepts, it would be easier to re-create new software than to scale an existing one.
 Cost- As hardware industry has shown its skills and huge manufacturing has lower down
the price of computer and electronic hardware. But the cost of software remains high if
proper process is not adapted.
 Dynamic Nature- The always growing and adapting nature of software hugely depends
upon the environment in which the user works. If the nature of software is always
changing, new enhancements need to be done in the existing one. This is where software
engineering plays a good role.
 Quality Management- Better process of software development provides better and
quality software product.

CHARACTERESTICSOFGOODSOFTWARE
A software product can be judged by what it offers and how well it can be used. This software
must satisfy on the following grounds:
 Operational
 Transitional
 Maintenance
Well-engineered and crafted software is expected to have the following characteristics:
Operational
This tells us how well software works in operations. It can be measured on:
 Budget
 Usability
 Efficiency
 Correctness
 Functionality
 Dependability
 Security
 Safety
Transitional
This aspect is important when the software is moved from one platform to another:
 Portability
 Interoperability
 Reusability
 Adaptability
Maintenance
This aspect briefs about how well a software has the capabilities to maintain itself in the ever-
changing environment:
 Modularity
 Maintainability

 Flexibility
 Scalability
In short, Software engineering is a branch of computer science, which uses well-defined
engineering concepts required to produce efficient, durable, scalable, in-budget and on-time
software products.

LECTURE NOTE-2
SOFTWARE DEVELOPMENT LIFE CYCLE
Software Development Life Cycle (SDLC) is a well-defined, structured sequence of stages in
software engineering to develop the intended software product.
SDLCACTIVITIES
SDLC provides a series of steps to be followed to design and develop a software product
efficiently. SDLC framework includes the following steps:
Fig 1: SDLC framework

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.
Requirement Gathering
This step onwards the software development team works to carry out the project. The team
holds discussions with various stakeholders from problem domain and tries to bring out as
much information as possible on their requirements. The requirements are contemplated and
segregated into user requirements, system requirements and functional requirements. The
requirements are collected using a number of practices as given -
 studying the existing or obsolete system and software
 conducting interviews of users and developers
 referring to the database
 collecting answers from the questionnaires.
Feasibility Study
After requirement gathering, the team comes up with a rough plan of software process. At this
step the team analyzes if the software can be made to fulfill all requirements of the user and if
there is any possibility of the software being no more useful. If the project is financially,
practically and technologically feasible for the organization to take up, they take up the project
else they let it go.
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.
Testing
An estimate says that 50% of whole software development process should be tested. Errors may
ruin the software from critical level to its own removal. Software testing is done while coding
by the developers and thorough testing is conducted by testing experts at various levels of code
such as module testing, program testing, product testing, in-house testing and testing the
product at user’s end. Early discovery of errors and their remedy is the key to reliable software.
Integration
Software may need to be integrated with the libraries, databases and other program(s). This
stage of SDLC is involved in the integration of software with outer world entities.
Implementation
This means installing the software on user machines. At times, software needs post-installation
configurations at user end. Software is tested for portability and adaptability and integration
related issues are solved during implementation.
Operation and Maintenance
This phase confirms the software operation in terms of more efficiency and less errors. If
required, the users are trained on, or aided with the documentation on how to operate the
software and how to keep the software operational. The software is maintained timely by
updating the code according to the changes taking place in user end environment or technology.
This phase may face challenges from hidden bugs and real-world unidentified problems.
Disposition
As time elapses, the software may decline on the performance front. It may go completely
obsolete or may need intense up gradation. Hence a pressing need to eliminate a major portion
of the system arises. This phase includes archiving data and required software components,
closing down the system, planning disposition activity and terminating system at appropriate
end-of-system time.

THE NEED FOR A SOFTWARE LIFE CYCLE MODEL
The development team must identify a suitable life cycle model for the particular project and
then adhere to it. Without using of a particular life cycle model the development of a software
product would not be in a systematic and disciplined manner. When a software product is being
developed by a team there must be a clear understanding among team members about when and
what to do. Otherwise it would lead to chaos and project failure. This problem can be illustrated
by using an example. Suppose a software development problem is divided into several parts and
the parts are assigned to the team members. From then on, suppose the team members are
allowed the freedom to develop the parts assigned to them in whatever way they like. It is
possible that one member might start writing the code for his part, another might decide to
prepare the test documents first, and some other engineer might begin with the design phase of
the parts assigned to him. This would be one of the perfect recipes for project failure. A software
life cycle model defines entry and exit criteria for every phase. A phase can start only if its
phase-entry criteria have been satisfied. So without software life cycle model the entry and exit
criteria for a phase cannot be recognized. Without software life cycle models it becomes difficult
for software project managers to monitor the progress of the project.
SOFTWAREDEVELOPMENTPARADIGM
The software development paradigm helps developer to select a strategy to develop the
software. A software development paradigm has its own set of tools, methods and procedures,
which are expressed clearly and defines software development life cycle. A few of software
development paradigms or process models are defined as follows:
CLASSICAL WATERFALL MODEL
Classical waterfall model is the simplest model of software development paradigm. It says the
all the phases of SDLC will function one after another in linear manner. That is, when the first
phase is finished then only the second phase will start and so on.

Fig 2: Waterfall Model
This model assumes that everything is carried out and taken place perfectly as planned in the
previous stage and there is no need to think about the past issues that may arise in the next
phase. This model does not work smoothly if there are some issues left at the previous step. The
sequential nature of model does not allow us go back and undo or redo our actions.
This model is best suited when developers already have designed and developed similar
software in the past and is aware of all its domains.
ITERATIVE MODEL
This model leads the software development process in iterations. It projects the process of
development in cyclic manner repeating every step after every cycle of SDLC process.
Fig 3: Iterative Model

The software is first developed on very small scale and all the steps are followed which are
taken into consideration. Then, on every next iteration, more features and modules are designed,
coded, tested and added to the software. Every cycle produces a software, which is complete in
itself and has more features and capabilities than that of the previous one.
After each iteration, the management team can do work on risk management and prepare for the
next iteration. Because a cycle includes small portion of whole software process, it is easier to
manage the development process but it consumes more resources.

LECTURE NOTE -3
PROTOTYPING MODEL
A prototype is a toy implementation of the system. A prototype usually exhibits limited
functional capabilities, low reliability, and inefficient performance compared to the actual
software. A prototype is usually built using several shortcuts. The shortcuts might involve using
inefficient, inaccurate, or dummy functions. The shortcut implementation of a function, for
example, may produce the desired results by using a table look-up instead of performing the
actual computations. A prototype usually turns out to be a very crude version of the actual
system.
Following is the stepwise approach to design a software prototype:
1. Basic Requirement Identification: This step involves understanding the very basic
product requirements especially in terms of user interface. The more intricate details of
the internal design and external aspects like performance and security can be ignored at
this stage.
2. Developing the initial Prototype: The initial Prototype is developed in this stage, where
the very basic requirements are showcased and user interfaces are provided. These
features may not exactly work in the same manner internally in the actual software
developed and the workarounds are used to give the same look and feel to the customer in
the prototype developed.
3. Review of the Prototype: The prototype developed is then presented to the customer and
the other important stakeholders in the project. The feedback is collected in an organized
manner and used for further enhancements in the product under development.
4. Revise and enhance the Prototype: The feedback and the review comments are discussed
during this stage and some negotiations happen with the customer based on factors like,
time and budget constraints and technical feasibility of actual implementation. The
changes accepted are again incorporated in the new Prototype developed and the cycle
repeats until customer expectations are met.

Fig 4: Prototype Model
SPIRAL MODEL
The Spiral model of software development is shown in fig.5. The diagrammatic representation of
this model appears like a spiral with many loops. The exact number of loops in the spiral is not
fixed. Each loop of the spiral represents a phase of the software process. For example, the
innermost loop might be concerned with feasibility study. The next loop with requirements
specification, the next one with design, and so on. Each phase in this model is split into four
sectors (or quadrants) as shown in the fig.5. The following activities are carried out during each
phase of a spiral model.
Fig 5: Spiral Model

- First quadrant (Objective Setting)
• During the first quadrant, it is needed to identify the objectives of the phase.
• Examine the risks associated with these objectives.
- Second Quadrant (Risk Assessment and Reduction)
• A detailed analysis is carried out for each identified project risk.
• Steps are taken to reduce the risks. For example, if there is a risk that the requirements
are inappropriate, a prototype system may be developed.
- Third Quadrant (Development and Validation)
• Develop and validate the next level of the product after resolving the identified risks.
- Fourth Quadrant (Review and Planning)
• Review the results achieved so far with the customer and plan the next iteration around
the spiral.
• Progressively more complete version of the software gets built with each iteration
around the spiral.

LECTURE NOTE -4
REQUIREMENT ANALYSIS & SPECIFICATION
The software requirements are description of features and functionalities of the target system.
Requirements convey the expectations of users from the software product. The requirements
can be obvious or hidden, known or unknown, expected or unexpected from client’s point of
view.
RequirementEngineering
The process to gather the software requirements from client, analyze and document them is
known as requirement engineering.
The goal of requirement engineering is to develop and maintain sophisticated and descriptive
‘System Requirements Specification’ document.
RequirementEngineeringProcess
It is a four step process, which includes –
 Feasibility Study
 Requirement Gathering
 Software Requirement Specification
 Software Requirement Validation
Let us see the process briefly -
Feasibility study
When the client approaches the organization for getting the desired product developed, it comes
up with rough idea about what all functions the software must perform and which all features
are expected from the software.
Referencing to this information, the analysts does a detailed study about whether the desired
system and its functionality are feasible to develop.
This feasibility study is focused towards goal of the organization. This study analyzes whether
the software product can be practically materialized in terms of implementation, contribution of
project to organization, cost constraints and as per values and objectives of the organization. It

explores technical aspects of the project and product such as usability, maintainability,
productivity and integration ability.
The output of this phase should be a feasibility study report that should contain adequate
comments and recommendations for the management about whether or not the project should be
undertaken.
Requirement Gathering
If the feasibility report is positive towards undertaking the project, next phase starts with
gathering requirements from the user. Analysts and engineers communicate with the client and
end-users to know their ideas on what the software should provide and which features they want
the software to include.
Software Requirement Specification
SRS is a document created by the system analyst after the requirements are collected from
various stakeholders.
SRS defines how the intended software will interact with hardware, external interfaces, speed of
operation, response time of system, portability of software across various platforms,
maintainability, speed of recovery after crashing, Security, Quality, Limitations etc.
The requirements received from client are written in natural language. It is the responsibility of
system analyst to document the requirements in technical language so that they can be
comprehended and useful by the software development team.
SRS should come up with following features:
 User requirements are expressed in natural language.
 Technical requirements are expressed in structured language, which is used inside the
organization.
 Design description should be written in pseudo code.
 Format of Forms and GUI screen prints.
 Conditional and mathematical notations for DFDs etc.

Software Requirement Validation
After requirement specifications are developed, the requirements mentioned in this document
are validated. User might ask for illegal, impractical solution or experts may interpret the
requirements incorrectly. This results in huge increase in cost if not nipped in the bud.
Requirements can be checked against following conditions -
 If they can be practically implemented
 If they are valid and as per functionality and domain of software
 If there are any ambiguities
 If they are complete
 If they can be demonstrated
RequirementElicitationProcess
Requirement elicitation process can be depicted using the following diagram:
Fig 1: Requirement elicitation process
 Requirements gathering - The developers discuss with the client and the end users and
know their expectations from the software.
 Organizing Requirements - The developers prioritize and arrange the requirements in
order of importance, urgency and convenience.
 Negotiation & discussion - If the requirements are ambiguous or there are some
conflicts in the requirements of various stakeholders, it is then negotiated and discussed
with the stakeholders. Requirements may then be prioritized and reasonably
compromised.
The requirements come from various stakeholders. To remove the ambiguity and
conflicts, they are discussed for clarity and correctness. Unrealistic requirements are
compromised reasonably.
 Documentation - All formal & informal, functional and non-functional requirements are
documented and made available for next phase processing.

RequirementElicitationTechniques
Requirements Elicitation is the process to find out the requirements for an intended software
system by communicating with client, end users, system users and others who have a stake in
the software system development.
There are various ways to discover requirements
Interviews
Interviews are strong medium to collect requirements. Organization may conduct several types
of interviews such as:
 Structured (closed) interviews, where every single information to be gathered, is decided
in advance, they follow the pattern and matter of discussion firmly.
 Non-structured (open) interviews, where information to gather is not decided in advance,
more flexible and less biased.
 Oral interviews
 Written interviews
 One-to-one interviews which are held between two persons across the table.
 Group interviews which are held between groups of participants. They help to uncover
any missing requirement as numerous people are involved.
Surveys
Organization may conduct surveys among various stakeholders by querying about their
expectation and requirements from the upcoming system.
Questionnaires
A document with pre-defined set of objective questions and respective options is handed over to
all stakeholders to answer, which are collected and compiled.
A shortcoming of this technique is, if an option for some issue is not mentioned in the
questionnaire, the issue might be left unattended.
Task analysis
Team of engineers and developers may analyze the operation for which the new system is
required. If the client already has some software to perform certain operation, it is studied and
requirements of proposed system are collected.

Domain Analysis
Every software falls into some domain category. The expert people in the domain can be a great
help to analyze general and specific requirements.
Brainstorming
An informal debate is held among various stakeholders and all their inputs are recorded for
further requirements analysis.
Prototyping
Prototyping is building user interface without adding detail functionality for user to interpret the
features of intended software product. It helps giving better idea of requirements. If there is no
software installed at client’s end for developer’s reference and the client is not aware of its own
requirements, the developer creates a prototype based on initially mentioned requirements. The
prototype is shown to the client and the feedback is noted. The client feedback serves as an input
for requirement gathering.
Observation
Team of experts visits the client’s organization or workplace. They observe the actual working
of the existing installed systems. They observe the workflow at client’s end and how execution
problems are dealt. The team itself draws some conclusions which aid to form requirements
expected from the software.

LECTURE NOTE-5
SOFTWAREREQUIREMENTCHARACTERISTICS
Gathering software requirements is the foundation of the entire software development project.
Hence they must be clear, correct and well-defined.
A complete Software Requirement Specifications must be:
 Clear
 Correct
 Consistent
 Coherent
 Comprehensible
 Modifiable
 Verifiable
 Prioritized
 Unambiguous
 Traceable
 Credible source
SoftwareRequirements
We should try to understand what sort of requirements may arise in the requirement elicitation
phase and what kinds of requirements are expected from the software system.
Broadly software requirements should be categorized in two categories:
Functional Requirements: Requirements, which are related to functional aspect of software fall
into this category. They define functions and functionality within and from the software system.
EXAMPLES -
 Search option given to user to search from various invoices.
 User should be able to mail any report to management.
 Users can be divided into groups and groups can be given separate rights.
 Should comply business rules and administrative functions.
 Software is developed keeping downward compatibility intact.

Non-Functional Requirements: Requirements, which are not related to functional aspect of
software, fall into this category. They are implicit or expected characteristics of software, which
users make assumption of.
Non-functional requirements include -
 Security
 Logging
 Storage
 Configuration
 Performance
 Cost
 Interoperability
 Flexibility
 Disaster recovery
 Accessibility
Requirements are categorized logically as
 Must Have: Software cannot be said operational without them.
 Should have: Enhancing the functionality of software.
 Could have: Software can still properly function with these requirements.
 Wish list: These requirements do not map to any objectives of software.
While developing software, ‘Must have’ must be implemented, ‘Should have’ is a matter of
debate with stakeholders and negation, whereas ‘could have’ and ‘wish list’ can be kept for
software updates.
UserInterface(UI)requirements
UI is an important part of any software or hardware or hybrid system. A software is widely
accepted if it is -
 easy to operate
 quick in response
 effectively handling operational errors
 providing simple yet consistent user interface

User acceptance majorly depends upon how user can use the software. UI is the only way for
users to perceive the system. A well performing software system must also be equipped with
attractive, clear, consistent and responsive user interface. Otherwise the functionalities of
software system cannot be used in convenient way. A system is said be good if it provides
means to use it efficiently. User interface requirements are briefly mentioned below -
 Content presentation
 Easy Navigation
 Simple interface
 Responsive
 Consistent UI elements
 Feedback mechanism
 Default settings
 Purposeful layout
 Strategically use of color and texture.
 Provide help information
 User centric approach
 Group based view settings.
SoftwareSystemAnalyst
System analyst in an IT organization is a person, who analyzes the requirement of proposed
system and ensures that requirements are conceived and documented properly & correctly. Role
of an analyst starts during Software Analysis Phase of SDLC. It is the responsibility of analyst
to make sure that the developed software meets the requirements of the client.
System Analysts have the following responsibilities:
 Analyzing and understanding requirements of intended software
 Understanding how the project will contribute in the organization objectives
 Identify sources of requirement
 Validation of requirement
 Develop and implement requirement management plan
 Documentation of business, technical, process and product requirements

 Coordination with clients to prioritize requirements and remove and ambiguity
 Finalizing acceptance criteria with client and other stakeholders
SoftwareMetricsandMeasures
Software Measures can be understood as a process of quantifying and symbolizing various
attributes and aspects of software.
Software Metrics provide measures for various aspects of software process and software
product.
Software measures are fundamental requirement of software engineering. They not only help to
control the software development process but also aid to keep quality of ultimate product
excellent.
Let us see some software metrics:
 Size Metrics - LOC (Lines of Code), mostly calculated in thousands of delivered source
code lines, denoted as KLOC.
Function Point Count is measure of the functionality provided by the software. Function
Point count defines the size of functional aspect of software.
 Complexity Metrics - McCabe’s Cyclomatic complexity quantifies the upper bound of
the number of independent paths in a program, which is perceived as complexity of the
program or its modules. It is represented in terms of graph theory concepts by using
control flow graph.
 Quality Metrics - Defects, their types and causes, consequence, intensity of severity and
their implications define the quality of product.
The number of defects found in development process and number of defects reported by
the client after the product is installed or delivered at client-end, define quality of
product.
 Process Metrics - In various phases of SDLC, the methods and tools used, the company
standards and the performance of development are software process metrics.
 Resource Metrics - Effort, time and various resources used, represents metrics for
resource measurement.

LECTURE NOTE-6
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.
Software design is the first step in SDLC (Software Design Life Cycle), which moves the
concentration from problem domain to solution domain. It tries to specify how to fulfill the
requirements mentioned in SRS.
SoftwareDesignLevels
Software design yields three levels of results:
 Architectural Design - The architectural design is the highest abstract version of the
system. It identifies the software as a system with many components interacting with
each other. At this level, the designers get the idea of proposed solution domain.
 High-level Design- The high-level design breaks the ‘single entity-multiple component’
concept of architectural design into less-abstracted view of sub-systems and modules and
depicts their interaction with each other. High-level design focuses on how the system
along with all of its components can be implemented in forms of modules. It recognizes
modular structure of each sub-system and their relation and interaction among each other.
 Detailed Design- Detailed design deals with the implementation part of what is seen as a
system and its sub-systems in the previous two designs. It is more detailed towards
modules and their implementations. It defines logical structure of each module and their
interfaces to communicate with other modules.
Modularization
Modularization is a technique to divide a software system into multiple discrete and
independent modules, which are expected to be capable of carrying out task(s) independently.
These modules may work as basic constructs for the entire software. Designers tend to design
modules such that they can be executed and/or compiled separately and independently.

Modular design unintentionally follows the rules of ‘divide and conquer’ problem-solving
strategy this is because there are many other benefits attached with the modular design of a
software.
Advantage of modularization:
 Smaller components are easier to maintain
 Program can be divided based on functional aspects
 Desired level of abstraction can be brought in the program
 Components with high cohesion can be re-used again
 Concurrent execution can be made possible
 Desired from security aspect
Concurrency
Back in time, all softwares were meant to be executed sequentially. By sequential execution we
mean that the coded instruction will be executed one after another implying only one portion of
program being activated at any given time. Say, a software has multiple modules, then only one
of all the modules can be found active at any time of execution.
In software design, concurrency is implemented by splitting the software into multiple
independent units of execution, like modules and executing them in parallel. In other words,
concurrency provides capability to the software to execute more than one part of code in parallel
to each other.
It is necessary for the programmers and designers to recognize those modules, which can be
made parallel execution.
Example
The spell check feature in word processor is a module of software, which runs alongside the
word processor itself.

LECTURE NOTE-7
COUPLING&COHESION
When a software program is modularized, its tasks are divided into several modules based on
some characteristics. As we know, modules are a set of instructions put together in order to
achieve some tasks. They are though, considered as single entity but may refer to each other to
work together. There are measures by which the quality of a design of modules and their
interaction among them can be measured. These measures are called coupling and cohesion.
Cohesion
Cohesion is a measure that defines the degree of intra-dependability within elements of a
module. The greater the cohesion, the better is the program design.
There are seven types of cohesion, namely –
 Co-incidental cohesion - It is unplanned and random cohesion, which might be the result
of breaking the program into smaller modules for the sake of modularization. Because it
is unplanned, it may serve confusion to the programmers and is generally not-accepted.
 Logical cohesion - When logically categorized elements are put together into a module,
it is called logical cohesion.
 Temporal Cohesion - When elements of module are organized such that they are
processed at a similar point in time, it is called temporal cohesion.
 Procedural cohesion - When elements of module are grouped together, which are
executed sequentially in order to perform a task, it is called procedural cohesion.
 Communicational cohesion - When elements of module are grouped together, which are
executed sequentially and work on same data (information), it is called communicational
cohesion.
 Sequential cohesion - When elements of module are grouped because the output of one
element serves as input to another and so on, it is called sequential cohesion.
 Functional cohesion - It is considered to be the highest degree of cohesion, and it is
highly expected. Elements of module in functional cohesion are grouped because they all
contribute to a single well-defined function. It can also be reused.

Coupling
Coupling is a measure that defines the level of inter-dependability among modules of a
program. It tells at what level the modules interfere and interact with each other. The lower the
coupling, the better the program.
There are five levels of coupling, namely -
 Content coupling - When a module can directly access or modify or refer to the contents
of another module, it is called content level coupling.
 Common coupling- When multiple modules have read and write access to some global
data, it is called common or global coupling.
 Control coupling- Two modules are called control-coupled if one of them decides the
function of the other module or changes its flow of execution.
 Stamp coupling- When multiple modules share common data structure and work on
different part of it, it is called stamp coupling.
 Data coupling- Data coupling is when two modules interact with each other by means of
passing data (as parameter). If a module passes data structure as parameter, then the
receiving module should use all its components.
Ideally, no coupling is considered to be the best.
DesignVerification
The output of software design process is design documentation, pseudo codes, detailed logic
diagrams, process diagrams, and detailed description of all functional or non-functional
requirements.
The next phase, which is the implementation of software, depends on all outputs mentioned
above.
It is then becomes necessary to verify the output before proceeding to the next phase. The early
any mistake is detected, the better it is or it might not be detected until testing of the product. If
the outputs of design phase are in formal notation form, then their associated tools for
verification should be used otherwise a thorough design review can be used for verification and
validation.

By structured verification approach, reviewers can detect defects that might be caused by
overlooking some conditions. A good design review is import ant for good software design,
accuracy and quality.

LECTURE NOTE-8
SOFTWARE ANALYSIS & DESIGN TOOLS
Software analysis and design includes all activities, which help the transformation of
requirement specification into implementation. Requirement specifications specify all functional
and non-functional expectations from the software. These requirement specifications come in
the shape of human readable and understandable documents, to which a computer has nothing to
do.
Software analysis and design is the intermediate stage, which helps human-readable
requirements to be transformed into actual code.
Let us see few analysis and design tools used by software designers:
DataFlowDiagram
Data flow diagram is a graphical representation of data flow in an information system. It is
capable of depicting incoming data flow, outgoing data flow and stored data. The DFD does not
mention anything about how data flows through the system.
There is a prominent difference between DFD and Flowchart. The flowchart depicts flow of
control in program modules. DFDs depict flow of data in the system at various levels. DFD does
not contain any control or branch elements.
Types of DFD
Data Flow Diagrams are either Logical or Physical.
 Logical DFD - This type of DFD concentrates on the system process and flow of data in
the system. For example in a Banking software system, how data is moved between
different entities.
 Physical DFD - This type of DFD shows how the data flow is actually implemented in
the system. It is more specific and close to the implementation.

DFD Components
DFD can represent Source, destination, storage and flow of data using the following set of
components -
Fig 1: DFD Components
 Entities - Entities are source and destination of information data. Entities are represented
by rectangles with their respective names.
 Process - Activities and action taken on the data are represented by Circle or Round-
edged rectangles.
 Data Storage - There are two variants of data storage - it can either be represented as a
rectangle with absence of both smaller sides or as an open-sided rectangle with only one
side missing.
 Data Flow - Movement of data is shown by pointed arrows. Data movement is shown
from the base of arrow as its source towards head of the arrow as destination.
Levels of DFD
 Level 0 - Highest abstraction level DFD is known as Level 0 DFD, which depicts the
entire information system as one diagram concealing all the underlying details. Level 0
DFDs are also known as context level DFDs.

Fig 1: Level 0 DFD of Online Shopping System
 Level 1 - The Level 0 DFD is broken down into more specific, Level 1 DFD. Level 1
DFD depicts basic modules in the system and flow of data among various modules. Level
1 DFD also mentions basic processes and sources of information.
Fig 2: Level 1 DFD of Online Shopping System

 Level 2 - At this level, DFD shows how data flows inside the modules mentioned in
Level 1.
Higher level DFDs can be transformed into more specific lower level DFDs with deeper
level of understanding unless the desired level of specification is achieved.

LECTURE NOTE-9
STRUCTURECHART
Structure chart is a chart derived from Data Flow Diagram. It represents the system in more
detail than DFD. It breaks down the entire system into lowest functional modules, describes
functions and sub-functions of each module of the system to a greater detail than DFD.
Structure chart represents hierarchical structure of modules. At each layer a specific task is
performed.
Here are the symbols used in construction of structure charts -
 Module - It represents process or subroutine or task. A control module branches to more
than one sub-module. Library Modules are re-usable and invokable from any module.
Fig 3: Modules in a structure chart
 Condition - It is represented by small diamond at the base of module. It depicts that
control module can select any of sub-routine based on some condition.

Fig 4: Condition in a structure chart
 Jump - An arrow is shown pointing inside the module to depict that the control will jump
in the middle of the sub module.
Fig 5: Jump in a structure chart
 Loop - A curved arrow represents loop in the module. All sub-modules covered by loop
repeat execution of module.

Fig 6: Loop in a structure chart
 Data flow - A directed arrow with empty circle at the end represents data flow.
Fig 7: Data Flow in a structure chart
 Control flow - A directed arrow with filled circle at the end represents control flow.
Fig 7: Control Flow in a structure chart
StructuredEnglish
Most programmers are unaware of the large picture of software so they only rely on what their
managers tell them to do. It is the responsibility of higher software management to provide
accurate information to the programmers to develop accurate yet fast code.
Other forms of methods, which use graphs or diagrams, may are sometimes interpreted
differently by different people.

Hence, analysts and designers of the software come up with tools such as Structured English. It
is nothing but the description of what is required to code and how to code it. Structured English
helps the programmer to write error-free code.
Other forms of methods, which use graphs or diagrams, may are sometimes interpreted
differently by different people. Here, both Structured English and Pseudo-Code tries to mitigate
that understanding gap.
Structured English uses plain English words in structured programming paradigm. It is not the
ultimate code but a kind of description what is required to code and how to code it. The
following are some tokens of structured programming.
IF-THEN-ELSE,
DO-WHILE-UNTIL
Analyst uses the same variable and data name, which are stored in Data Dictionary, making it
much simpler to write and understand the code.
Example
We take the same example of Customer Authentication in the online shopping environment.
This procedure to authenticate customer can be written in Structured English as:
Enter Customer_Name
SEEK Customer_Name in Customer_Name_DB file
IF Customer_Name found THEN
Call procedure USER_PASSWORD_AUTHENTICATE()
ELSE
PRINT error message
Call procedure NEW_CUSTOMER_REQUEST()
ENDIF

The code written in Structured English is more like day-to-day spoken English. It cannot be
implemented directly as a code of software. Structured English is independent of programming
language.
Pseudo-Code
Pseudo code is written more close to programming language. It may be considered as augmented
programming language, full of comments and descriptions.
Pseudo code avoids variable declaration but they are written using some actual programming
language’s constructs, like C, Fortran, Pascal etc.
Pseudo code contains more programming details than Structured English. It provides a method
to perform the task, as if a computer is executing the code.
Example
Program to print Fibonacci up to n numbers.
void function Fibonacci
Get value of n;
Set value of a to 1;
Set value of b to 1;
Initialize I to 0
for (i=0; i< n; i++)
{
if a greater than b
{
Increase b by a;
print b;
}
else if b greater than a
{
increase a by b;

LECTURE NOTE-10
DECISIONTABLES
A Decision table represents conditions and the respective actions to be taken to address them, in
a structured tabular format.
It is a powerful tool to debug and prevent errors. It helps group similar information into a single
table and then by combining tables it delivers easy and convenient decision-making.
Creating Decision Table
To create the decision table, the developer must follow basic four steps:
 Identify all possible conditions to be addressed
 Determine actions for all identified conditions
 Create Maximum possible rules
 Define action for each rule
Decision Tables should be verified by end-users and can lately be simplified by eliminating
duplicate rules and actions.
Example
Let us take a simple example of day-to-day problem with our Internet connectivity. We begin by
identifying all problems that can arise while starting the internet and their respective possible
solutions.
We list all possible problems under column conditions and the prospective actions under column
actions.
Conditions/Actions Rules
Conditions
Shows Connected N N N N Y Y Y Y
Ping is Working N N Y Y N N Y Y
Opens Website Y N Y N Y N Y N

Actions
Check network cable X
Check internet router X X X X
Restart Web Browser X
Contact Service provider X X X X X X
Table 1: Decision Table – In-house Internet Troubleshooting
Entity-RelationshipModel
Entity-Relationship model is a type of database model based on the notion of real world entities
and relationship among them. We can map real world scenario onto ER database model. ER
Model creates a set of entities with their attributes, a set of constraints and relation among them.
ER Model is best used for the conceptual design of database. ER Model can be represented as
follows:
Fig 8: ER Model
 Entity - An entity in ER Model is a real world being, which has some properties
called attributes. Every attribute is defined by its corresponding set of values,
called domain.
For example, consider a school database. Here, a student is an entity. Student has
various attributes like name, id, age and class etc.
 Relationship - The logical association among entities is called relationship.
Relationships are mapped with entities in various ways. Mapping cardinalities define the
number of associations between two entities.

Mapping cardinalities:
o one to one
o one to many
o many to one
o many to many
DataDictionary
Data dictionary is the centralized collection of information about data. It stores meaning and
origin of data, its relationship with other data, data format for usage etc. Data dictionary has
rigorous definitions of all names in order to facilitate user and software designers.
Data dictionary is often referenced as meta-data (data about data) repository. It is created along
with DFD (Data Flow Diagram) model of software program and is expected to be updated
whenever DFD is changed or updated.
Requirement of Data Dictionary
The data is referenced via data dictionary while designing and implementing software. Data
dictionary removes any chances of ambiguity. It helps keeping work of programmers and
designers synchronized while using same object reference everywhere in the program.
Data dictionary provides a way of documentation for the complete database system in one place.
Validation of DFD is carried out using data dictionary.
Contents
Data dictionary should contain information about the following
 Data Flow
 Data Structure
 Data Elements
 Data Stores
 Data Processing

Data Flow is described by means of DFDs as studied earlier and represented in algebraic form as
described.
= Composed of
{} Repetition
() Optional
+ And
[ / ] Or
Example
Address = House No + (Street / Area) + City + State
Course ID = Course Number + Course Name + Course Level + Course Grades
Data Elements
Data elements consist of Name and descriptions of Data and Control Items, Internal or External
data stores etc. with the following details:
 Primary Name
 Secondary Name (Alias)
 Use-case (How and where to use)
 Content Description (Notation etc. )
 Supplementary Information (preset values, constraints etc.)
Data Store
It stores the information from where the data enters into the system and exists out of the system.
The Data Store may include -
 Files
o Internal to software.
o External to software but on the same machine.

o External to software and system, located on different machine.
 Tables
o Naming convention
o Indexing property
Data Processing
There are two types of Data Processing:
 Logical: As user sees it
 Physical: As software sees it

REFERENCES
BIBLIOGRAPHY
1. “Fundamentals of Software Engineering”, Rajib Mall, Prentice-Hall of India.
WEBLIOGRAPGY
2. http://www.tutorialspoint.com/

Lecture1422914635

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