Transcript CIS 301 - Expert systems

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Data Flow Diagrams class
file: dataflows.ppt
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Managerial mapping tools
• Budgets, financial reports
• Architectural and geographical
blueprints and maps
• Flowcharts
• Timelines, Gantt and Pert charts
• Mission statements
• Organizational charts
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Understanding & documenting
processes
• Entity-relationship models
– Show logical structure of data needed to
support business process
• Data flow diagrams
– Show what is done
• Flowcharts
– Show how it is done
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Information System
Analysis & Design
2 keys to Information System Development:
* Entity-Relationship Model - analysis and
design of information structure in a system.
* Data Flow Diagram - analysis and design
of the information flow (actually more of the
business processes) in a system.
Concept behind this traditional approach:
Procedure + Data Structure = Program
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E-R Diagrams
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Data Flow Diagrams (DFDs)
• DFDs are graphic representations of
systems
• DFDs map how data flows through
interconnected processes
• Although the name implies data, the
emphasis is on processes
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DFD symbols
• DFDs consist of only four symbols:
» Environmental (external) elements
» Processes
» Data Flows
» Data Storage
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DFD symbols
Environmental
(external)
elements
Processes
Data Flows
Data Storage
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Supplier
Accounting dept.
Print invoice
Compute net pay
invoice
General ledger
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Traditional Approach in DFD
Hierarchical Decomposition of Functions
- decomposing function process into
smaller ones which together
accomplish the function.
• Top Down Design
• Bottom Up Implementation
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DFD Examples
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Environmental elements
External elements are those that exist outside the
boundaries of the system.
They can be persons, organizations, or other systems.
In a way, they serve to define the system’s boundary.
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Data Flows
Data flows are any collection of logically related data
elements that travel from one process to another. They
can be of any size.
Think of a record, a note, a phone call, a letter, or a
file.
Data flows can converge or diverge, they can be one
or two way flows.
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Processes
Processes are transformations of inputs into outputs.
It is best to label each process as verb, or verb + object.
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Data Storage
Data stores hold data (while flows are about data-inmotion).
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Leveled Data Flow Diagrams
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Context level diagram
Level 0 diagram (“top level”)
Level n figures (diagrams)
pyramid, granularity.
How deep?
Structured English, pseudocode,
flowcharts?
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Steps to develop DFD (1)
Conceptualize data flows from top down–
1. Make a list of business activities and use it to
determine various:external entities, data flows, processes,
data stores.
2. Create a Context Diagram: with external
entities and data flows to and from the system
- which is the only process, labeled as #0.
The Context DFD should not have any data
stores, nor any detailed processes.
3. Draw the next level DFD - Diagram 0.
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Steps to develop DFD (2)
3. Draw the next level DFD ΠDiagram 0. It
should show major business processes and
possible data stores at this level.
4. Create a Child Diagram for each process in
Diagram 0, exploding if necessary.
5. Check for errors and designate good names.
6. Use the DFD to reason about improving the
operation by re-organizing business processes.
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Context level diagrams
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Use only a single process model
Process represents entire system
No numbers
All external entities
Show all in- and outflows of info
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“Figure “n” diagrams
• Each level “explodes” one process on
preceeding level
• Each level numbered for process it
explodes
• Include up to seven processes on
single diagram
• Stopping rule?
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Exploding…
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Diagramming guidelines
• Label each data flow: use unique names
• Keep data flow names constant across
levels
• Avoid (diagnose) read-only processes
• Write-only processes are only allowed
under one condition...
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Creating Diagram 0
1. Start with input from an external entity:
What happens to this data entering the system?
Is it stored?
Is it input for several processes?
2. Work backwards from output data flow:
Where does this data come from?
Is it calculated on demand, or was it stored in a file?
3. Examine data flow to and from a data store:
Which processes put data into the store?
Which processes use the data?
Which processes are responsible for update?
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Whither and Why DFDs?
• (Most?) Natural way to document a
system
• Simple, common communication
• Simple, common language
• Supported by- and support the creation
of CASE
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Accounts Payable Problem
Consider the following scenario.
Each month you receive bills from various vendors (e.g., phone, auto insurance,
credit cards, utilities) and periodically other billings (e.g., magazine subscriptions,
university tuition and fees). Consider all of these billings as being examples of
invoices from vendors. Like most people you don't pay your bills on the same day
that they are received but rather review each invoice and prioritize them in terms
of which you will pay first. These reviewed and prioritized invoices are then
placed in an old shoe box until you decide you had better start paying some of
them.
You remove an invoice from the shoe box and prepare a check to be mailed to the
vendor. You check the old balance in your check register and update the register
with the check information and compute a new balance. You may do this several
times a month.
At the end of the month you receive a statement from your bank that lists the
checks that have cleared your account. You (should) take your check register and
compare your list of checks and their amounts with the statement that you
received from the bank. If everything is in balance then you place an appropriate
mark in your check book else you enter a correcting entry (the bank never makes
a mistake).
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Accounts Payable (AP) DFD
Invoice
Vendor
Vendor
Invoice
1.0
Approve &
Prioritize
Bills
Check
Prioritized
Bills
Check
AP
Statement
Bank
Check Info
and New
Balance
2.0
Prepare
Check
Selected Bill
Shoe Box
Old Balance
Check Register
Context
Diagram
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Balanced Checkbook
Register
Info
3.0
Compare
Statement
Bank
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Order Entry Problem
SAM's is a mail order catalogue store. A customer fills out the sales order form that
is enclosed in the catalogue and mails it to their headquarters in the Bahamas
(postage prepaid). Upon receipt, a clerk opens the envelopes and removes the
sales order forms. The clerk gives the forms to a data entry operator, who keys the
data onto a diskette using a microcomputer. After data entry, the sales orders are
filed in a Sales Order History file. The diskette containing all of the sales order
data is then read by a minicomputer. For each ordered item, the Inventory Master
Record is retrieved from the Inventory master files and the balance on-hand is
reduced by the ordered amount. The updated Inventory Master Record is written
back to the file. The same program prints picking tickets and writes a Daily Sales
Report file onto the system disk. The picking tickets are input to the order filling
system where they are used by warehouse personnel in picking the merchandise
from the shelves for shipment to the customers. Another minicomputer program
reads the Daily Sales Report file and prepares a daily sales report that goes to the
sales manager.
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Sales Order (SO) DFD
Customer
Sales
Order
Order
Filling
Station
Daily
Sales
Report
Sales
Manager
Context Diagram
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Sales
Order
1.0
Open Mail
Sales Order Form
Process
Sales
Order
Picking
Tickets
Customer
2.0
Sales Order
Enter Order Entered
Sales Orders History File
Entered
Sales
Inventory Master Records
3.0
to be updated
Update
Inventory
Inventory
Master File
Master File Updated
Inventory Master Records
Daily
Order
Sales
Picking Filling
4.0
Tickets Station
Print Daily
Sales
Sales Report
Manager
Daily Sales Report
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Prepare Check Flowchart for
AP 2.0
Start
Remove next bill
Get balance
Balance
GT Bill
? Yes
Write Check
Update Register
Yes
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More
Bills?
No
Stop
No
Return
bill to box
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Open Mail Flowchart for SO 1.0
Start
Start
Open Mail
Open Mail
Remove Sales Order
Remove Sales Order
Place in Pile
Take
S.O. to
Operator
Yes
More
Mail?
No
Stop
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Yes
More
Mail?
Take
pile to
Operator
Stop