Date post: | 28-Dec-2015 |
Category: |
Documents |
Upload: | rosemary-scott |
View: | 217 times |
Download: | 0 times |
During systems development both processes and data must be modeled◦ Data modeling describes data used by system◦ Process modeling describes processes carried out by
system Level of detail
◦ Varies between highest summary and lowest detail◦ Structured tools enable level of detail to be varied
Restrict a single DFD to no more than six to eight processes
Use another tool to document the lowest level of detail but use no more than a single page.
B-3
Graphic representation of a system that uses a small number of symbol shapes to illustrate how data flows through interconnected processes ◦ Most natural way to document processes◦ Emphasis on processes rather than data
B-4
Customer
Sales1Order
Rejected Order
Dispatch Note
2 Warehouse
Dispatch Goods
3 Accounts
Maintain Credit Ratings
D1 Credit Rating
Check Credit Rating
A Complete DFD
Data Flow Diagrams (DFDs) show:
•The processes within the system
•The datastores (files) supporting its operation
•The information flows within it
•The system boundary
•Interactions with external entities
DFDs consist of four symbols1) Environmental elements called terminators / external
entity Person Organization Another system
2) Processes which transform inputs to outputs Labeled with verb and object Also labeled with system or computer program name
B-8
DFD symbols [cont.]◦ Data flows which consist of logically related data elements
that travel from one point or process to another. In other words, data in motion. Structures Diverge Converge
◦ Data stores which are data repositories. In other words, data at rest.
B-9
Customer
Sales
Check Credit Rating
D1 Credit Rating
A Data Flow
An External Entity
A Process
A Data Store
3
DFD Symbols
Sales
Check Credit Rating
3
Unique Number Where it’s done
What’s done
Output DataInput Data
The Process Symbol
Accounts
Maintain Credit Rating
3
Sales
Check Credit Rating
1
M = Manual data Store
D = Computer File
D1 Credit Rating
Writing/Updating
Reading
The data store symbol
Sales
Check Credit Rating
3
D1 Credit Rating
The Data Flow Symbol
Customer Balance
Use Meaningful names
Self Evident Data Flows need
not be named
The External Entity Symbol
Customer
System Boundary
A Source and/or sink of data outside the system boundry
DFD dikelompokkan menjadi 2:◦ Logical DFD
Fokus pada bisnis dan bagaimana bisnis berjalan How the system will be constructed
◦ Physical DFD How the system will be implemented Include hardware, software, files, people yang
terlibat dalam sistem
2 Dispatch Goods
2
1
Process
2.1
Dispatch
Note
Validated
Order
Levelling – to avoid complex DFDs, processes can be grouped into higher level processes
Customer
Sales1Order
Rejected Order
Dispatch Note
2 Warehouse
Dispatch Goods
3 Accounts
Maintain Credit Ratings
D1 Credit Rating
Check Credit Rating
A Complete DFD
Customer
D1 Credit Rating
A Duplicated External Entity
Duplicated Data Store
Customer
Repeated Symbols – to avoid crossing lines, data
stores and external entities can be repeated:
Level 1
Level 2
E F D
Elementary
Functional
Description
Get cust dets
If order>cred
refer
Else
raise order
…..
DFD Levels
A wines and spirits wholesaler stocks a range of approximately 400 different lines and delivers by van on regular weekly runs to customers who are mainly off-licenses and clubs. The majority of orders are received by telephone and any one customer may place several orders during the week which must be accumulated and delivered in one consignment. When a customer telephones he expects to be advised on the availability of an item requested and, if not in stock, the alternatives that are available. At present, sales order forms are filled in by the telephone salesmen and sent to the warehouse where they are used for the despatch of the items. Hand-written despatch notes are used as the basis of the invoices which are typed and sent by post sometime later.
Prepare a dataflow diagram (DFD) which represents the above system.
Sample
Developing Dataflow Diagrams
1. Identify external entities
2. Draw context diagram
3. Who/Where does what
4. Identify datastores
5. Draw diagram
External Entities
1. Customer
Context Diagram
customer company
order
invoice
advice
des. note + goods
What Where/who
Receive orders Sales
Accumulate orders Sales
Advise availability Sales
Complete Sales Order Form Sales
Despatch Items Warehouse
Write despatch notes Warehouse
Type Invoices Warehouse
Send Invoices Warehouse
Datastore
Stock file
customer
customer
Stock file
Accumulate orders
Advise availability
Complete forms
1 Sales
Sales Order Forms
2
Produce despatch notes
Produce Invoices
InvoiceDespatch note + goods
Warehouse
Draw DFD
OrderAdvice
M1