Requirement Analysis Tools in Software Engineering (Part 01)

  

Requirement Analysis Tools

Traditional structured methods (P+D)

• Entity relationship diagrams (ERD)
• Data Flow Diagrams (DFDs)
• Entity State Transition diagrams

Object Oriented methods (O-O)

• Use Case Diagrams
•  Class Diagrams
• Sequence Diagrams
• State Transition Diagrams

Entity Relationship Diagrams

Data Flow Diagrams

Context Diagram

A First Level DFD

Process specification

Internal Specification

• Pseudo code specification
• Decision Tables

External specification

• Pre-condition-Post condition

Process specification - Pseudo code

Verify customer ID  (DFD process 1.0)

Upon insertion of the customer’s ATM card

  check the ATM-card-no against the lost-stolen-list

If the entered ATM-card-no is on the lost-stolen-list  Then

      Retain card and suspend processing

If the entered ATM-card-no is not on the lost-stolen-list Then

    Repeat

        Prompt customer for his PIN

        Compare the entered PIN to the PIN listed in the Bank’s database for this customer

    Until

        the customer has entered his correct PIN  or

        fails to correctly enter his PIN after 3 attempts

If a valid PIN has been entered  Then

       Continue processing

Else

       Suspend processing

      Return ATM card

 

Process specification - Decision Table

Calculate new balances (DFD Process 4.1)

Process specification - An External specification

pre-condition – what must be true for the function to execute correctly

post-condition -  What is guaranteed to be true after the function executes

Example : A merge function may be specified as follows

     merge(item1:array,item2 : array) : newArray

Pre

    SizeOf (item1)>0, SizeOf(item2)>0,  (both arrays have at least one element)

    item1[i] <item1[i+1],  1<i<noOfitems1  (in order)

    item2[i] <item2[i+1],  1<i<noOfitems2  (in order)

Post

     SizeOf(newArray)=SizeOf(item1) + SizeOf(item2)

     newArray[i] < newArray[i+1],  1<i<SizeOf(newArray)

These are all testable

 

Data   Specification

All dataflows in DFDs   should be specified using a combination of elementary dataflows or previously defined dataflows.

The following symbols can be used in dataflow specifications

    and                             +

    or                              [  ]

   repeat                       {   }

   optional                    (    )

   comment                  *    *

 

Data specification

Examples:

Acct-designation   =  1{alphanumeric-character}15

Acct-number         =  8{numeric-character}8

Amount                 =  rupees+cents

Acct-selection       =  [savings/checking/loan-acct/credit-card]

                                  (acct-designation)

Cust-acct-list        = 1{acct-designation+acct-number}8

Balance-display    =  * display of current balance to customer*

 

Requirement Specification practice– Good

Use a form based approach

  *  Describe each function in separate form

 

Function                    :   obtain balance

Description               :   on request, returns the balance for a  

                                       customer account

Inputs                        :   Account number, PIN

Source                        :   Keypad

Outputs                      :   Account balance

Destination                :   Screen display

Requires                    :   Customer has inserted card and entered PIN

Pre-condition             :   Card is from member bank

Post-condition           :    Balance is displayed

Side effects                :    None