SWE-401 - 6. Software Analysis and Design Tools

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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:
Data Flow Diagram
Data Flow Diagram (DFD) is a graphical representation of flow of data 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. It 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 -
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Software Analysis and
Design Tools
Prepared By: Ghayour Abbas

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 Entities - Entities are sources and destinations 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.
 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.

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 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.
Structure Charts
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.

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 Condition - It is represented by small diamond at base of the module. It
depicts that control module can select any of sub-routine based on some
condition.
 Jump - An arrow is shown pointing inside the module to depict that the
control will jump in the middle of the sub-module.
 Loop - A curved arrow represents loop in the module. All sub-modules
covered by loop repeat execution of module.

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 Data flow - A directed arrow with empty circle at the end represents data
flow.
 Control flow - A directed arrow with filled circle at the end represents
control flow.
HIPO Diagram
Hierarchical Input Process Output (HIPO) diagram is a combination of two
organized methods to analyze the system and provide the means of
documentation. HIPO model was developed by IBM in year 1970.
HIPO diagram represents the hierarchy of modules in the software system. Analyst
uses HIPO diagram in order to obtain high-level view of system functions. It

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decomposes functions into sub-functions in a hierarchical manner. It depicts the
functions performed by system.
HIPO diagrams are good for documentation purpose. Their graphical
representation makes it easier for designers and managers to get the pictorial idea
of the system structure.
In contrast to Input Process Output (IPO) diagram, which depicts the flow of
control and data in a module, HIPO does not provide any information about data
flow or control flow.
Example
Both parts of HIPO diagram, Hierarchical presentation, and IPO Chart are used for
structure designing of software program as well as documentation of the same.

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Structured English
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.
Different methods, which use graphs or diagrams, at times might be interpreted
in a different way 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. 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

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The code written in Structured English is more like day-to-day spoken English. It
can not 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.

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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;
print a;
}
}
Decision Tables
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

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 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
Do no action
Table : Decision Table – In-house Internet Troubleshooting
Entity-Relationship Model
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.

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ER Model is best used for the conceptual design of database. ER Model can be
represented as follows :
 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:
 one to one
 one to many
 many to one
 many to many
Data Dictionary
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

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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)

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 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

SWE-401 - 6. Software Analysis and Design Tools

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SWE-401 - 6. Software Analysis and Design Tools