[attachment=11404]
Application System Modeling Data Modeling through ER Model
Context Level Diagram
Data Flow Diagram
1. It is a graphical tool for designing systems ,input ,process and output.
2. It represents flow of data through system.
3. It shows the processes ,data stores ,sources & destination entities .
4. The transformation of data from input to output through process is described logically.
5. The top level diagram is called context diagram. It contains single process .It gives a broad overview of the system under study.
6. There are two types of DFD.
a) Logical DFD
b) Physical DFD
Symbols used in DFD
 Steps to draw DFD
Developing DFD follows a top down process.
 An initial overview model (context level )is exploded into more detailed ,lower level diagrams. Each process is broken down into yet more detailed DFD. This is carried out repeatedly until sufficient detail is described.
 Steps.
1. Identify the sources i.e. entities which originate data and sinks which receive final output.
2. Identify the process as the activities of the system.
3. Join the process and sources/sinks via data flow.
4. The names of data stores ,sources & destinations are written in capital letters. Process & data flow names have the first letter of each word capitalized
5. Sources cannot leak data directly to a data store.
6. A data store cannot can not pass data directly to a destination.
7. Data cannot flow directly from one data store to another.
Physical DFD
1. The DFD that shows how things happen and which are the actual physical component involved. Specify where, how and by whom the processes are performed.
2. Shows the system’s entities & data flows into and out from each entity .
3. Process names include a noun may be the name of the processor i.e. person ,dept ,comp-sys etc.
4. Data stores identify their computer and manual implementation. (e.g. clerks notebook etc.)
5. Data flow names include the implementation facts as media ,timing, name etc Logical DFD
1. The DFD that a clear idea of what the system has to achieve without getting into details like “who is going to do it”. Specify what tasks/process the systems are doing.
2. Shows a system processes and data flows into and out of the processes .
3. Process name describe the work done. Process is labeled with verb that describes the activities being performed E.g. Order Processing
4. Physical location of data stores is irrelevant.
5. Data flow names describe the data they contain.
 Process modeling through Data Flow Diagrams (Logical / Physical)
Case study
Draw a PDFD and LDFD for order processing system
The activities include
1.Customer sends in order .
2.Orders are received by order processing clerk.
3.Order processing clerk verifies the order for the material before sending for further processing or rejecting it.
4.Rejected order will be sent to customer others will be entered into the computer file.
5.Order is processed and an invoice is prepared
 Process modeling through Data Flow Diagrams (Logical / Physical) (cont.)
 Context Level Diagram for Fixed Deposit System
First Level Diagram For FDS
 Case Study 1
 ABC Hotels Pvt. Ltd. Wants to develop a front-end office Management system having following functions:
1. Enquiry and Advance Booking
2. Services Management
3. Check –Out and Billing Process
4. A/c. Receivables
5. Generating Reports