requirements gathering and analysis - …€¦ · requirements gathering and analysis ... in the...

Darshan Institute of Engineering & Technology for Diploma Studies Unit-2

1 Dept: CE FSD ( 3341603) Piyush Bhut

REQUIREMENTS GATHERING AND ANALYSIS

The analyst starts requirement gathering activity by collecting all information that could be useful to

develop system.

In practice it is very difficult to gather all the necessary information from a large number of people and

documents and to form a clear understanding of a problem.

Availability of working model helps in gathering the requirement.

Studying the existing documentation

Analyst studies existing documents regarding system to be developed before visiting the customer site.

These documents are about the basic purpose, the stakeholders etc.

Interview

All different categories of users are interviewed to gather different functionalities required by them.

For example, to perform the requirements analysis of library automation software, the analyst might

interview the library members, the librarian, and the accountants.

Task analysis

The users usually view software as a black box that provides a set of service is also called a task. For

each identified task, the analyst tries to create the different steps necessary to the service in guidance

with the users.

For example, for the issue book service, the steps may be: authenticate user, check the number of

books issued to the customer and determine if the maximum number of books that this member can

borrow has been reached, check whether the book has been reserved, post the book issue details in

the member’s record, and finally print out a book issue slip that can be presented at the security

counter to take out the book.

Scenario analysis

A task can have many scenarios of operation. The different scenarios of a task can occur when the task

is invoked under different situations.

For different types of scenarios of a task, the behavior of the system can be different.

For example, the different scenarios for the book issue task of a library automation software may be:

Book issue service is satisfactorily performed and the book issue slip is printed.

The book is reserved and cannot be issued to the member.

The maximum number of books that can be issued by the member is exceeded, and the book

cannot be issued to the member.

REQUIREMENTS ANALYSIS

After requirements gathering is completed the analyst analyzes the gathered requirements to clearly

understand the exact customer requirements.

The main purpose of the requirement analysis activity is to analyze the collected information to obtain

a clear understanding of the product to be developed, with a view to removing all ambiguities,

incompleteness and inconsistencies.



The following basic questions should be clearly understood by the analyst:

What is the problem?

Why is it important to solve the problem?

What are the possible solutions to the problem?

What exactly are the data input to the system and what exactly are the data output by the system?

What are the complexities that might arise while solving the problem?

If there are external software or hardware with which the developed software has to interface,

then what exactly would the data interchange formats with the external system be?

When the analyst detects any inconsistencies, anomalies or incompleteness in the gathered

requirements, he resolves them by carrying out further discussions with the customers.

SOFTWARE REQUIREMENTS SPECIFICATION

After the analyst has gathered all the required information regarding the software to be developed and

has remove all incompleteness, inconsistencies, and anomalies from the specification he starts to

systematically organize the requirements in the form of an SRS document.

SRS document contains all the user requirements.

CHARACTERISTICS OF A GOOD SRS DOCUMENT

The important properties of a good SRS document are the following:

Correct

An SRS is correct if every requirement included in the SRS, required in the final system. Correctness

ensures that what is specified is done correctly.

Unambiguous

An SRS is unambiguous if and only if every requirement stated has one and only one interpretation.

Requirements are often written in natural language.

Complete

The SRS is complete if, and only if, it includes the following elements:

All requirements, whether relating to functionality, performance, design constraints, attributes, or

external interfaces.

Definition of the response of the software in all situations. Note that it is important to specify the

response to both valid and invalid input values.

Consistent

A consistent requirement does not conflict with other requirements in the requirement specification.

It does not duplicate.

Ranked for importance

The SRS is ranked for importance if, and only if, has an identifier to indicate the importance of the

particular requirement. Typically, all of the requirements that relate to a software product are not



equally important. Some requirements may be essential, especially, while others may be desirable.

Each requirement in the SRS should be identified to make these differences clear and explicit.

Verifiable

A requirement is verifiable if, and only if, there exists some process with which a person or machine

can check that the software product meets the requirement.

Modifiable

The SRS is modifiable if, and only if, its structure and style are such that any changes to the

requirement can be made easily, completely, and consistently.

Structured

The SRS is structured if, and only if, it is moduled, and easy to understand and modify. Over the time

customer requirements changes, requirement specification also changes. In order to make

modification to SRS it is necessary that SRS should be well structured.

Traceable

A traceable requirement has a unique identity or number.

REQUIREMENTS SPECIFICATION TYPES

Requirement specification activity is translating the gathered information during the analysis phase

into a document that defines a set of requirements. Two types of requirements may be included in this

document:

1. Customer Requirement

2. System Requirement

System Requirements are further classified into more two types.

i. Functional requirements

ii. Nonfunctional requirements

CUSTOMER (USER) REQUIREMENT

Customer requirements are high level abstract statements of the system requirement for the customer

and end user of the system.

These statements are in a natural language. It describes what services the system is expected to

provide to customer and the situation under which it must operate.

The customer requirement is quite general and simple.

SYSTEM REQUIREMENT

System requirements are a more detailed description of the functionality to be provided. It describes

what the system should do. The system requirements document should define exactly what is to be

implemented. The system requirements provide more specific information about the services and

function of the system.



Functional Requirements

The functional requirements discuss the functionalities expected from the system. These are

statements of services that provide how the system should react to particular inputs and how the

system should behave in particular situation. It describes the relationship between input and output. It

also state what the system should do if any situation occurs.

The system is considered to perform a set of high level functions. Each function of the system can be

considered as a transformation of set of input data to the corresponding set of output data. The user

can get some meaningful pieces of work done using a high level function.

Document the functional requirements of a system it is necessary to first learn to identify the high level

function of the system.

The high level function would be split into smaller sub requirement.

A high level function is one using which the user can get some useful piece of work done.

For example, the receipt printing work during withdrawal of money from an ATM is called a useful

piece of work? Receipt printing should not be considered a high-level requirement, because the user

Select withdraw cash

Enter option

Enter amount

Display account type

options

Prompt for amount to

be withdrawn

Insufficie-

nt balance

in account

Print

receipt

Enter amount in multiple of 100



does not specifically request for this activity. The receipt gets printed automatically as part of the

withdraw money function.

In a library automation software a high level functional requirement might be search-book. This

function involves accepting a book name or a set of keywords from the user running a matching

algorithm on the book list and finally outputting the matched books. The generated system response

can be in several form e.g. display on the terminal, a print out or transferred to the other system.

High level function usually involves a series of interactions between the system and one or more users.

For example as shown in figure user inputs have been represented by rectangles and the response

produced by the system by circles.

In figure the different scenarios occur depending on the amount entered for withdrawal. Different

behavior for different scenarios of the system for the same high level functions.

Nonfunctional requirements

Nonfunctional requirements deal with the characteristics of the system which cannot be expressed as

functions - such as the maintainability of the system, portability of the system, usability of the system,

maximum number of current users etc.

Nonfunctional requirements may include:

reliability issues

accuracy of results

Constraints on the system implementation, etc.

Example of a non functional requirement can be that the user interface of software should be usable

by factory shop floor worker who may not even have a high school degree.

DESIGN PROCESS

The design process is a sequence of steps that enable the designer to describe all aspects of the

software to be built. It describes how the system will be implemented and how it will work.

Software design deals with transforming the customer requirements, as described in the SRS

document, into appropriate form that is suitable for implementation in a programming language.

CLASSIFICATION OF DESIGN ACTIVITIES

The activities in the design process vary depending on the type of system being developed. The below

figure suggest that the stage of the design process are sequential. Design process can be classified as:

Architectural design, where you identify the overall structure of the system, the principal components

(sometimes called sub-systems or modules), and their relationships and how they are distributed. It

can be derived from DFD.

Interface design, where you define the interfaces between system components. It describes how

system communicate itself and with the user. It can be derived from DFD and state transition diagram.

Component design, where you take each system component and design how it will operate. This is

defined the expected functionality to be implemented. It can be derived from state transition diagram.



Database design, where you design the system data structures and how these are to be represented in

a database. The data objects and relationships defined in the ER diagram and the detailed data content

illustrated in the data dictionary. It can be derived from ER diagram.

CLASSIFICATION OF DESIGN METHODOLOGIES

A design methodology can be simply defined as a set of design procedure that one follows from the

beginning to the completion of the software development process.

The nature of the methodology is dependent on a number of factors including type of the software

being developed, requirements of the users, qualification and training of software development team,

available hardware and software resources.

There are fundamentally two different approaches:

1. Function oriented design: it can be further divided in two category

I. Structured Analysis

II. Structured Design

2. Object oriented design

Function oriented design (Top-Down approach) A function oriented design is viewed as something that performs a set of functions.

Starting at this high-level view of the system, each function is successively refined into more detailed

functions. Each of these sub-functions may be split into more detailed sub-functions and so on.

It can be further divided in two categories.

Structured Analysis

It is used to transform a textual problem description into graphical form.

It examines the detail structure of the system.

It defines the processes and data flow among these processes.

In structured analysis functional requirements specified in SRS are decomposed and analysis of data

flow is represented diagrammatically by DFD.

Structured Design

During Structured design all functions identified during analysis mapped to module structure and that

is useful for implementation.

The aim of structured design is to transform the results of the structured analysis (i.e. DFD) into a

structure chart. The structure chart is tree like diagram a popular way to represent the control

hierarchy in a high level design.

Object oriented design

In the Object oriented design approach the system is viewed as collection of objects (i.e. entities).

Object Oriented Design supports following object oriented concepts such as Abstraction, Information

Hiding, Functional Independence, and Modularity.

Design is the initial step in moving towards from the problem domain to the solution domain. A

detailed design includes specification of all the classes with its attributes, detailed interface. The



purpose of design is to specify a working solution that can be easily translated into a programming

language code.

UML modeling and Use Case are used in object oriented designing.

COHESION

Cohesion means the measure of the strength of function relatedness of elements within a module.

Elements include instructions, groups of instructions, data definition, and call of another module.

Cohesion means how closely the elements of a module are related to each other.

It represents how tightly bound the internal elements of the module are to one another.

The classification of cohesion are given beloved:

Coincidental cohesion

It is the lowest cohesion. A module is said to have coincidental cohesion, if it performs a set of tasks

that relate to each other very loosely. Means the module contains a random collection of functions.

For example, in a transaction processing system (TPS), the get-input, print-error, and summarize-

members functions are grouped into one module. The grouping does not have any relevance to the

structure of the problem.

Logical cohesion

A module is said to be logically cohesive, if all elements of the module perform similar operations.

An example of logical cohesion is the case where a set of print functions generating different output

reports are arranged into a single module.

Temporal cohesion

When a module contains functions that are related by the fact that all the functions must be executed

in the same time span, the module is said to temporal cohesion.

The set of functions for start-up, shutdown of some process, etc. exhibit temporal cohesion.

Procedural cohesion

A module is said to possess procedural cohesion, if the set of functions of the module are all part of a

procedure (algorithm) in which certain sequence of steps have to be carried out for achieving an

objective, e.g. the algorithm for decoding a message.

Communicational cohesion

A module is said to have communicational cohesion, if all functions of the module refer to or update

the same data structure, e.g. the set of functions defined on an array or a stack.

Sequential cohesion

A module is said to possess sequential cohesion, if the elements of a module form the parts of

sequence, where the output from one element of the sequence is input to the next.

For example, in a TPS, the get-input, validate-input, sort-input functions are grouped into one module.



Functional cohesion

It is the strongest cohesion.

Functional cohesion is said to exist, if all the elements of a module are related to perform a single task.

All the elements are achieving a single goal of a module.

For example, sort the array are examples of these module.

COUPLING

Coupling between two modules is a measure of the degree of interdependence or interaction between

the two modules.

It refers to the strengths of relationship between modules in a system. It indicates how closely two

modules interact and how they are independent.

As modules become more independent the coupling increases and loose coupling minimize

interdependency that is better for any system development.

If two modules interchange large amount of data then they are highly interdependent.

High coupling between modules make the system difficult to understand and increase the

development efforts. So low coupling is the best.

The classification of cohesion are given beloved:

Data coupling

Two modules are data coupled, if they communicate through a parameter. An example is an

elementary data item passed as a parameter between two modules, e.g. an integer, a float, a

character, etc.

It is lowest coupling and best for the software development.

Stamp coupling

Two modules are stamp coupled, if they communicate using a composite data item such as a record in

PASCAL or a structure in C.

Control coupling

Control coupling exists between two modules, if data from one module is used to direct the order of

instructions execution in another.

An example of control coupling is a flag set in one module and tested in another module.

Common coupling

Two modules are common coupled, if they share data through some global data items.

Content coupling

Content coupling exists between two modules, if they share code. That is a jump from one module into

the code of another module can occur. e.g. a branch from one module into another module.



DATA MODELING CONCEPTS

ER diagram represent a set of real-world entities and the logical relationships among them. This

diagram depicts entities, the relationships between them, and the attributes pictorially in order to

provide a high-level description of conceptual data models.

Once an ER diagram is created, the information represented by it is stored in the database. The

information depicted in an ER diagram is independent of the type of database and can later be used to

create database of any kind such as relational database, network database, or hierarchical database.

ER diagram includes data objects and entities, data attributes, relationships, cardinality and modality.

Data object

A data object is a real world entity or things.

Data object is a representation of composite information used by software.

Composite information refers to different features or attributes of a data object and this object can be

in any of the following forms: External entity, Event or Place etc.

An entity is the data that stores information about the system in a database. Examples of an entity is

student, department etc.

Data attributes

Data attributes describe the properties or characteristics of a data object.

Attributes that identify entities are known as key attributes. On the other hand, attributes that

describe an entity are known as non-key attributes.

Data attribute is used to perform the following functions: Naming an instance of data object,

Description of the instance, making reference to another instance in another table.

For example, attributes of 'account' entity are 'number', 'balance', and so on.

Similarly, attributes of 'user' entity are 'name', 'address', and 'age'.



Entities are represented by rectangles, attributes are represented by ellipses, and relationships are

represented by diamond symbols. A key attribute is also depicted by an ellipse but with a line below it.

Relationships

Entities are linked to each other in different ways. This link or connection of data objects or entities

with each other is known as relationship. Note that there should be at least two entities to establish a

relationship between them.

Once the entities are identified, the development team checks whether a relationship exists between

them. Relationship is represented using diamond shape symbol with joined relationship name.

Cardinality

Cardinality specifies the number of occurrences (instances) of one data object or entity that relates to

the number of occurrence of another data object or entity. It also specifies the number of entities that

are included in a relationship.

Different cardinalities are explained below:

One-to-one (1:1): Indicates that one instance of an entity is related only to one instance of another

entity. For example, in a bank, each user is related to only one account number.

One-to-many (1: M): Indicates that one instance of an entity is related to several instances of

another entity. For example, one user can have many accounts in different banks.

Many-to-many (M: M): Indicates that many instances of entities are related to several instances of

another entity. For example, many users can have their accounts in many banks.

Modality

Modality describes the possibility whether a relationship between two or more entities and data

objects is required. The modality of a relationship is 0 if the relationship is optional. However, the

modality is 1 if an occurrence of the relationship is essential.

For example, Customer entity is related to order entity. Here, cardinality for 'customer' entity indicates

that the customer places an order whereas modality for 'customer' entity indicates that it is necessary

for a customer to place an order.

Cardinality for 'order' indicates that a single user can place many orders whereas modality for 'order'

entity indicates that a user can arrive without any 'order'.



DATA FLOW DIAGRAM (DFD)

The DFD (also known as a bubble chart) is a hierarchical graphical model of a system that shows the

different processing activities or functions that the system performs and the data interchange among

these functions.

Each function is considered as a processing station (or process) that consumes some input data and

produces some output data. The system is represented in terms of the input data to the system,

various processing carried out on these data, and the output data generated by the system.

PRIMITIVE SYMBOLS OF DFD

A DFD model uses a very limited number of primitive symbols as shown in figure to represent the

functions performed by a system and the data flow among these functions.

External entity: The external entities are those physical entities external to the software system which

interact with the system by inputting data to the system or by consuming the data produce by the

system. External entity is represented by a rectangle. For example librarian, library member.

Function: A function is represented using a circle. This symbol is called a process or a bubble.

Data flow: A directed arc or an arrow is used as a data flow symbol. A data flow represents the data

flow occurring between two processes or between an external entity and a process in the direction of

the data flow arrow.

Data store: A data store is represented using two parallel lines. It represents a logical file. It represents

data structure or a physical file on disk. Each data store is connected to a process. The direction of the

data flow arrows shows whether data is being read from or written into a data store.

Output: The output symbol is as shown in figure. The output symbol is used when a hard copy is

produced.

DEVELOP DFD MODEL OF SYSTEM

A DFD model of a system graphically depicts the transformation of the data input to the system to the

final result through a hierarchy of levels.

The top level DFD is called the level 0 DFD or the context diagram.

A DFD starts with the most abstract definition of the system (lowest level) and at each higher level

DFD, more details are successively introduced.

To develop a higher-level DFD model, processes are decomposed into their sub-processes and the data

flow among these sub-processes is identified.

External entity Process Output

Data flow

Data store



To develop the data flow model of a system, first the most abstract representation of the problem is to

be worked out. The most abstract representation of the problem is also called the context diagram.

After, developing the context diagram, the higher-level DFDs have to be developed.

Context Diagram (Level 0)

The context diagram is the most abstract data flow representation of a system. It represents the entire

system as a single bubble. This bubble is labeled according to the main function of the system.

The various external entities with which the system interacts and the data flow occurring between the

system and the external entities are also represented. The data input to the system and the data

output from the system are represented as incoming and outgoing arrows. These data flow arrows

should be annotated with the corresponding data names.

The context diagram is also called as the level 0 DFD.

Level 1



Include all entities and data stores that are directly connected by data flow to the one process you are

breaking down.

Show all other data stores that are shared by the processes in this breakdown.

Decomposition at further level 1 DFD have processes with label 1.0, 2.0, 3.0,… and so on.

Shortcoming (Disadvantage) of DFD Model

DFDs for large system can be become complex, difficult to understand and time consuming. Data flow can become confusing to programmer if it is not well defined. DFD does not specify exactly in which order processes are executed. There are multiple possible ways

to execute processes. So several alternate presentations can be possible. In DFD which inputs are consumed and which outputs are produced are not specified. DFD does not provide clear view about decomposition of any process to its sub-process.

SCENARIO BASED MODELING

UNIFIED MODELING LANGUAGE (UML)

UML, as the name implies, is a modeling language.

It provides a set of notations (e.g. rectangles, lines, ellipses) to create a visual model of the system.

UML has its own syntax (symbols and sentence formation rules) and semantics (meanings of symbols

and sentences).

WRITING USE CASES

While developing software, it is essential for the development team to consider user satisfaction as a

top priority to make the software successful. For this, the development team needs to understand how

users will interact with the system.

This information helps the team to carefully identify each user requirements and then create a

meaningful and relevant analysis model and design model. For this, the software engineer creates

scenarios in the form of use-cases to describe the system from the users' view.

Use cases describe the tasks in which the users will use the software under a specific set of conditions.

Each use-case provides one or more scenarios in order to understand how a system should interact

with another system. Use cases do not provide descriptions about the implementation of software.

Use-cases are represented with the help of a use-case diagram, which indicate the relationships among

actors and use cases within a system.

A use-case diagram describes what exists outside the system (actors) and what should be performed

by the system (use-cases). The notations used to represent a use-case diagram are listed in Table.

Name Description

Actor Actors are different kinds of users who use the system in various ways. For example,

one actor can be a library user whereas another user can be part of the library staff.

Use-case Describes a specific instance of a system function.

Communication link Indicates the interaction between the actor and the system.

Use link Indicates that one of the use-case uses the behavior described by another use-case.



Customer (actor) uses bank ATM to check balances of his/her bank accounts, deposit funds, withdraw

cash and transfer funds (use cases). ATM Technician provides maintenance and repairs. All these use

cases also involve Bank actor whether it is related to customer transactions or to the ATM servicing.

Generalization

Use case generalization can be used when one use case that is similar to another, but does something

slightly differently or something more.

The child use case inherits the behavior and meaning of the parent use case.

The notation for generalization is as shown in figure.

Includes

The includes relationship involves one use case including the behavior of another use case.

The includes relationship occurs when a part of behavior that is similar across a number of use cases.

Pay membership

fee

Pay through

library pay card

Pay through

credit card

http://www.uml-diagrams.org/use-case-actor.html

http://www.uml-diagrams.org/use-case.html



The factoring of such behavior will help in not repeating the specification and implementation across

different use cases.

It is represented using a predefined stereotype <<include>>.

ACTIVITY DIAGRAM

An activity diagram illustrates the dynamic nature of a system by modeling the flow of control from

activity to activity. An activity represents an operation on some class in the system that results in a

change in the state of the system.

Typically, activity diagrams are used to model workflow or business processes and internal operation.

Basic Activity Diagram Symbols and Notations

Action states

Action states represent the actions of objects. You can draw an action state using a rectangle with

rounded corners.

Action Flow

Action flow arrows illustrate the relationships among action states.

Initial State

A filled circle followed by an arrow represents the initial action state.

Final State

An arrow pointing to a filled circle nested inside another circle represents the final action state.

Withdraw

cash

Customer

Authentication

Deposit

Funds

<<include>>

<<include>>



Branching

A diamond represents a decision with alternate paths. The outgoing alternates should be labeled with

a condition or guard expression. You can also label one of the paths "else."

For example, activity diagram of ATM machine

Synchronization

A synchronization bar helps illustrate parallel transitions. Synchronization is also called forking and

joining.

Swimlanes

Swimlanes group related activities into one column

.



ARCHITECTURAL DESIGN DECISIONS

Design and implementation

Software design and implementation is the stage in the software engineering process at which an

executable software system is developed.

Software design is a creative activity in which you identify software components and their

relationships, based on a customer’s requirements.

Implementation is the process of realizing the design as a program.

Software Architecture

The design process for identifying the sub-systems making up a system and the framework for sub-

system control and communication is architectural design.

The output of this design process is a description of the software architecture.

Architectural design decisions

Architectural design is a creative process so the process differs depending on the type of system being

developed.

However, a number of common decisions span all design processes and these decisions affect the non-

functional characteristics of the system.

Is there a generic application architecture that can be used?

How will the system be distributed?

What architectural styles are appropriate?

What approach will be used to structure the system?

How will the system be decomposed into modules?

How should the architecture be documented?

ARCHITECTURAL VIEWS

What views or look are useful when designing and documenting a system’s architecture?

What notations should be used for describing architectural models?

Each architectural model only shows one view or look of the system.

It might show how a system is decomposed into modules, how the run-time processes interact or the

different ways in which system components are distributed across a network.

For both design and documentation, you usually need to present multiple views of the software

architecture.

4 + 1 view model of software architecture

1. A logical view, which shows the key concepts of the system as objects and classes.

2. A process view, which shows how, at run-time, the system, is composed of interacting processes.

3. A development view, which shows how the software is decomposed for development. Means it shows

the breakdown of software into modules.

4. A physical view, which shows the system hardware and how software components are distributed

across the processors in the system.



ARCHITECTURAL PATTERNS

Patterns are a means of representing, sharing and reusing knowledge.

An architectural pattern is a stylized description of good design practice, which has been tried and

tested in different environments.

Patterns should include information about when they are and when they are not useful.

MVC (Model-View-Controller) Pattern

The system is structured into three logical components that interact with each other. The Model

component manages the system data and associated operations on that data. The View component

manages how the data is presented to the user. The Controller component manages user interaction

(e.g., key presses, mouse clicks, etc.) and passes these interactions to the View and the Model.

Used when there are multiple ways to view and interact with data.

Allows the data to change independently of its representation and vice versa.

Layered architecture Pattern

Organizes the system into layers with related functionality associated with each layer. A layer provides services to the layer above it so the lowest-level layers represent core services that are likely to be used throughout the system.



Client-server

In client–server architecture, the functionality of the system is organized into services, with each

service delivered from a separate server. Clients are users of these services and access servers to make

use of them.

Used when data in a shared database has to be accessed from a range of locations. Because servers

can be replicated, may also be used when the load on a system is variable.

The principal advantage of this model is that servers can be distributed across a network. General

functionality (e.g., a printing service) can be available to all clients and does not need to be

implemented by all services.

APPLICATION ARCHITECTURES

Software application architecture is the process of defining a structured solution that meets all the

technical and operational requirements.

Application architecture is the organizational design of an entire software application including all sub

component and external applications.

Application architecture helps us to understand the operations of the system.

It describes the layout of application’s deployment.

Use of application architectures

As a starting point for architectural design.

As a way of organizing the work of the development team.

As a means of assessing components for reuse.

As a vocabulary for talking about application types.

requirements gathering and analysis - …€¦ · requirements gathering and analysis ... in the...

Documents