Sdp Ch3 Lect2 2q5854

Sofware Design DFD

Software Design • Software design is an iterative process through which requirements are translated into a “blueprint” for constructing the software.

Data flow diagram • Data flow diagram is not a flowchart • DFD is a graphical representation of “Flow ” of data through an information system • It views a system as a function that transform the input in to desired output. • Flowchart shows flow of control • Data flow diagram show flow of data. • Processes in DFD can operate in parallel • DFDs processes can change timely, flowcharts are constant.

Creating a DFD • Steps – Create a list of activities – Create context level DFD (identifies external entities and processes) – Construct Level 0 DFD (identifies manageable subprocess) – Construct Level 1-n DFD (identifies actual data flow and data stores)

Symbols for DFD

• A few simple guidelines for derivation of a data flow diagram: (1) the level 0 data flow diagram should depict the software/system as a single bubble; (2) primary input and output should be carefully noted; (3) refinement should begin by isolating candidate processes, data objects, and data stores to be represented at the next level; (4) all arrows and bubbles should be labeled with meaningful names; (5) information flow continuity must be maintained from level to level, and (6) one bubble at a time should be refined. There is a natural tendency to overcomplicate the data flow diagram. This occurs when you attempt to show too much detail too early.

Context level DFD ( Level 0) for Safe home

Level 1 DFD

DFD level 2

• The refinement of DFDs continues until each bubble performs a simple function. That is, until the process represented by the bubble performs a function that would be easily implemented as a program component.

Examples for DFD construction • Tic Tac toe game

Level 0 (Context DFD)

Level 1 DFD

Supermarket example • A supermarket needs to develop the following software to encourage regular customers. For this, the customer needs to supply his/her residence address, telephone number, and the driving license number. Each customer who s for this scheme is assigned a unique customer number (CN) by the computer. A customer can present his CN to the check out staff when he makes any purchase. In this case, the value of his purchase is credited against his CN. At the end of each year, the supermarket intends to award surprise gifts to 10 customers who make the highest total purchase over the year. Also, it intends to award a 22 caret gold coin to every customer whose purchase exceeded Rs.10,000. The entries against the CN are the reset on the day of every year after the prize winners’ lists are generated.

Level 0

Level 1

Level 2

System Architecture for ATM

Next letcure • Use case • Activity

Use case Diagram