1. DFD Properties

2. Agenda  DFD Components  DFD Properties  DFD Decomposition  DFD Advantages  Example

3. DFD Components System Boundary Outside Inside Process 4 Name Name should be verb+object Data Flow name C Name Data Store employee-id Employee-Record Make EID Numbers and letter are used as short-hand references; names should be evocative or descriptive

4. DFD Properties: Logical Dependency 2 Do 3 Finish 1 Begin a b c d f e g h h depends on e and g; e depends on d and c; c depends on a and b. Thus h depends on g, e, d, c, b, and a. But h does not depend on f or i. Logically, h also depends on processes 3, 2, and 1. i

5. Decomposition 0 Top 3 HighC 2 HighB 1 HighA Process “Top” is composed of three sub- processes: HighA, HighB, and HighC. 3.1 LowA 3.2 LowB Process “HighC” is composed of two subprocesses: LowA and LowB

6. Decomposition - 2 Top LowestA11LowestA12LowestA13 LowestA21LowestA22LowestA23 MidA1MidA2 LowALowB HighAHighBHighC At each level, a process is decomposed into a set of simpler processes at the next level. Those without components are “Basic” processes. Those with components have the job of coordinating the component processes. At each level, the set of inputs and outputs for the set of components exactly equals those of the process at the next higher level. In effect, low level processes are “zoom ins” of higher level ones.

7. DFD Advantages  Logical dependencies help diagnose problems such as bad data, redundancy, bottlenecks, etc.  Flow characteristics can be used to calculate loads, volumes, rates, etc.  System boundary helps limit research efforts, avoid drifting

8. Example Customer Supplier Sales Manager Customer- info Order-info CVerification 1 3 4 6 8 7 5 2 Customer- order A B C D Product- Profiles Sales- Records Customer- Profiles Sales- Reports Product- Info SVerification Suppl- ier-info Supplier- Product No-product- reply Cust-data Negative- response Cust-data Sales-data Cust-info- request CI- reply Sales - request Cannot-sell- reply Sales - record Updated- sales - record E Distribution- List Report - request Report – Receiver- Info Sales- Report Process Names: 1. Handle Order Request 2. Inform Customer 3. Check Product Availability 4. Handle Product Information 5. Check Customer Quality 6. Create Sales Request 7. Record Sale 8. Distribute Sales Report Each Process may consist of subprocesses Diagnosis: How can a sales record exist without a sale? Rate of request can be determined. Where is bottleneck?