Al Khawarizmi International College, Al Ain , U.A.E

Al Khawarizmi International College,Al Ain , U.A.E

Software Development

Module Code: CST 240

Chapter 4: Software Design

Lecturer:Karamath Ateeq

Chapter 4: Software Design2

OutlineSoftware Design Approaches:• Function –Oriented design Methodology: SSADM Major Tools: DFD, ER Diagram• Object –Oriented Design Methodology: OOP-Object Modeling using UML

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Features of function-Oriented Design:

1 .A system is viewed as something that performs a set of functions. Starting from high level, each function is successively

refined into more detailed functions. Eg: create-new-library consists of the following sub functions :

( 1 )assign-membership –number( 2 )create-member-record

( 3)Print-bill2 .The system state is centralized and shared among different

functions Eg: Data such as member-records is shared among

( 1)create-new-member( 2)delete-member

( 3 )update-member-record




Object –Oriented Vs Function –Oriented Design:

•Unlike Function –Oriented Design methods ,in OOD, the basic abstractions are not real –world functions like sort, display etc but real- world entities such as employee ,picture ,machine ,radar system etc.

•In OOD, state information is not represented in a centralized shared memory but is distributed among the objects of the system.

•Function –Oriented techniques, such as SA/SD, group functions together as if they constitute a high level function . On the other hand Object –Oriented techniques group the functions together on the basis of the data they operate on


SSADM- Structured System Analysis and Design Method.

SSADM uses a combination of three techniques:

(1) Logical Data Modeling- The processing of identifying, modeling and documenting the data. The data is separated into entities and relationships between the entities.

(2) Data Flow Modeling- The processing of identifying, modeling and documenting how the data moves around the system. It examines the processes, data stores, external entities and data flows.

(3) Entity Behavior Modeling-The processing of identifying, modeling and documenting the events that affect each entity and the sequence in which these events occur.



SSADM application development projects are divided into five modules:

1. Feasibility study.

2. Requirements Analysis.

3. Requirements Specification.

4. Logical System Specification.

5. Physical Design.



Advantages of using SSADM:

Unlike rapid application development , which conducts steps in parallel , SSADM builds each step on the work that was prescribed in the previous step ,with no deviation from

the model .

It has a control over the project and has the ability to develop better quality systems .



Context Analysis Diagram• The context diagram represents the entire

system under investigation.• The components of a context diagram are

– Process : Shows the main process of the system.

– External entities : External Entity is a source or destination of the data, e.g a person, supplier, department, or another system.

– Data flows : The data flow shows the flow of data from an external entity to the process and vice-versa.



Data-flow Diagram• Data-flow diagrams illustrate how data

flows through a system and how the output is derived from the input through a sequence of functional transformations.



DFD ComponentsThe components are

• any external entity that interact with the system,

• the system processes,

• the data stored by these process,

• and the data flows in the system.



DFD Symbols

• Data flow diagrams use a number of symbols to represent systems components. Several different versions of symbols are used to construct DFD's. Two major versions are:– Yourdan /Demarco– Gane/Sarson



Yourdan /DemarcoGane/Sarson

Process

Data store

External Entity

Source/destination

dataflow

DFD Symbols



External entity• External entity is a source or destination of

a data flow which is outside the area of study.

• Represents organizations, agents, or people, outside the system under study.

• Duplicate external entity is shown as


CustomerCustomer

CustomerCustomer


Process• Processes represent the transformation of data

as it flows thorough the system.• Each process symbol has its unique identifying

number (such as 1.0,2.0, 2.1.2 and so on) • Process symbol should also be labeled with

purpose or type of process to occur. The label should be a unique and expressing a strong statement of action on an object such as update inventory, create order etc

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Process• The location specification at the bottom of

the symbol is optional. It is used strictly as documentation, to show either where the process occurs or who is responsible for it.


4.0

VERIFY ORDER

Purchase dept

IdentificationDescription of

the function

Location (opt.)


Data Store• Data Store is a repository where the data

is stored.

• It can be a data base or file on a tape or disk, or it can be a manual medium such as filing cabinet.


DescriptionID

D1 Customer data


Data Flow• Data flow show the flow of information

from an entity to a process or a process to a data store or vice-versa.

• Any one end of a data flow must be connected to a process.

CustomerCustomerCustomer - order Verify

order

1.0



Do’s and Don'tsDo’sDon’ts


DFD Levels• Level 0 DFD : The level 0 DFD shows only

the main processes of the system. Ideally 7-9 processes can be shown in Level 0 DFD. Processes are numbered as 1.0,2.0,3.0 and so forth.

• Level 1DFD : The Level 1 DFD is created to explode any one process of the level 0 DFD. Level 1 DFD, for process 1 in level 0 DFD, will be numbered as 1.1,1.2,1.3 etc.



DFD TypesThere are two types of DFDs:

• Logical DFD:

• Physical DFD:

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Logical vs Physical DFDDesign FeaturesLogical DFDPhysical DFDWhat the model depicts/shows

How the business operates

How the system will be implemented

What the process represents

Business activatesPrograms and manual procedures

What does the data store represent

Collection of data, regardless of how the data is stored.

Physical files and databases, manual files.

Types of data storesShows the permanent data collection

Master files, transaction files. Any processes that operate at two different times must be connected by a data store.



Logical DFD guidelinesData flows:• Physical DFDs corresponds to things like

business forms, documents, reports, terminal displays, spoken communication such as phone calls etc. But logical data flows are implementation independent.

• A logical DFD represents the minimum, essential data necessary needed by the process that receives the data flow.



Logical DFD GuidelinesData flows:

• Logical dataflow names should be descriptive adjectives and nouns.

• Data flow names should be singular and not plural.



Logical Process:• Logical processes depicts what work or action

has been performed on incoming data flows to produce outgoing data flows and not who or what is doing that work or activity.

• Examples:– Credit customer account– Update inventory– Verify account.

Logical DFD Guidelines



Logical Data Store:• Logical data store are very different from

the physical data store.• Physical data store corresponds to

implementations such as databases, files, file cabinets, log sheets, books etc.

• In contrast , the logical data stores represent the businesspeople, objects and events about which we need to store data.

Logical DFD Guidelines



Practical• Draw CAD and DFD for the given case study.• The operation theater of Al Noor Hospital requires a computerized system to maintain the details of the

patient who undergo operations. A patient comes to the ward with an admission note from a doctor. The patient is admitted in a ward of the hospital for an operation. Before admitting the patient the personal details of the patient is obtained and an admission file is open and an operation note is given to the patient. The information of each operation conducted in the hospital has to be maintained separately. Al Noor hospital gives special discount to some patients according to their policy. The policy should include details of discount given. On a daily basis a report of patients undergoing an operation the next day should be generated by the system. This report is given to the management. Another report should be generated for the doctor that gives details of the number of operations he has the next day. After the operation, when a patient has to be discharged a patient-discharge note is given to the patient.

• Draw a Context diagram and Data Flow diagram or the given case study.

•



Data Dictionary• A data dictionary lists all data items

appearing in the DFD model of a system.

• The data items listed include all data flows and the contents of all data stores appearing on all DFD’s in the DFD model of a system.

• The data flows on the context diagram can be used as a start of the data dictionary



A data dictionary plays a very important role in any software development process because of the following reasons:

• It provides a standard terminology for all relevant data for use by all engineers working in the same project.

• It helps the analyst to know the component elements of a data structure.

• Data dictionary also serves as basis for creating systems database.


Benefits of Data Dictionary


Components of Data Dictionary• Data Flow: Data flow is usually the first

component to be defined.• Data Store: Data’s are stored here.• Data element: The most basic piece of

data that can’t be broken into more detailed unit is called data element.

• Data structures: Combinations of data elements make up data structures i.e. a meaningful set of data elements.



Data Dictionary Types• Logical data dictionary: It needs only

data elements name like the description of the item, its number, color, size, price, quantities etc.,

• Physical data dictionary: It might include data element names along with some characteristics of those elements e.g. field size, checks/controls/validation, data store/s using those elements etc.



Data Dictionary Rules The terms used for data structures should be capital Name having multiple words are hyphenated(-) e.g

ITEM-DESC Assigned names should be straight forward and

user oriented There should be a name for each data flow, data

store, data structure, data element No two data flows should have the same name A data flow should not have more than one name

and aliases (nick names) must be discouraged



Data Flow Example


Sl noData Flow Name

TypeData structureDescription

1customer information

formCustomerCustomers personal details are obtained from this form

Note: Data Flow types can be Form, Note, Paper list, Letter etc


Data Store• When data flow elements are grouped to

form a structural record, a data store is created for each unique structured record.

• One data store may contain several data structures.



Data Store Examples


Data store No

Data Store NameData Element

D1CustomersCustomer_id, customer_name, address, phone


Data StructureData Structure Symbols

• = means “equivalent”

• + means “and”

• {} means “repeating data element”

• [|] means “either one data element or another”

• ( ) means “optional data element”



• CUSTOMER = customer_id +CUSTOMER_NAME+ADDRESS+phone

CUSTOMER_NAME= first_name + (middle_name) + last_name

ADDRESS = (street) + p.o.box+ city

Data Structure example



• PAYMENT = payment_id + payment_date+customer_id + total_amount + payment_mode + [credit_card_no | check_number] +

{ item_id + item_name +qty + unit_price +amount}


Data Structure example


Data Element• Data element is the smallest unit which

cannot be divided further.• Each data element must be defined once

in data dictionary.• Input/output format symbols:

X - May enter or display any character9 - Enter or display only numbers, - insert comma into a numeric display

- - separator



Data Element Examples


SlnoData elementTypeSizeFormatValidation

Default value

1Customer_idNumeric6999999Must be unique

Nil

2First_namecharacter25X(25)Cannot be left blank

nil

3Citycharacter20X(20)Cannot be left blank

Abu Dhabi

4Phonecharacter 1099-9999999Only numbers

nil


E-R Diagram• Entity Relationship Diagram shows the

relationship between the tables in a database.

• The relationship can be– One- to – One– One- to many– Many -to -many





Introduction to UML• UML stands for Unified Modelling

Language

• UML is emerging as a standard modelling language Object Oriented Modelling.

• It is useful for graphically depicting object-oriented analysis and design models



UML• UML allows to represent multiple views of

a system using a variety of graphical diagrams:

• Use-Case Diagram

• Class Diagram

• State Diagram

• Sequence Diagram

• Collaboration Diagram



UML• Use Case

• A use-case model consists of actors and use cases.

• It helps us to get the functional requirement of the system.

• Use case gives a complete sequence of related actions initiated by an actor to accomplish a specific goal.



UML• Class Diagram: It shows the main

concepts and techniques in object modelling.

• State Diagram: A state diagram depicts the various state transitions or changes an object can experience during its lifetime.

• Interaction between use cases is shown using two diagrams called– Sequence Diagram – Collaboration Diagram



Use-case Diagram

User

Lending service

User administration

Supplier Catalogue services

Library

LibraryStaff



Class Diagram



State Diagram

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