1. Process Models: Data Flow Diagrams
Special thanks goes to Dr. Jack T. Marchewka for many of the ideas and examples contained in these notes.

2. Process Modeling Objective:
Understand the concept of business processes
Understand and create Data Flow Diagrams.

3. DFDs Visually represent Emphasize the logic of system
data flows
processes
Emphasize the logic of system
Provide documentation for Analysis & Design

4. Data Flow Diagrams Data Flow Process File or Data Store
Source or Entity
Gane & Sarson Methodology

5. DFDs Do not show technical aspects
Show interrelations of systems & subsystems
Facilitates
developer understanding
user-developer communication
Completeness of data & process definitions

6. The Systems Concept
Output
Input
Process

7. DFDs 1
Data Flow
Input
Data Flow
Output
Process

8. Developing DFDs Context Diagram Zero Level Explosion
System Overview
Little or no detail
Zero Level Explosion
More detailed
First,Second, Third Levels
More detailed levels

9. Context DFD Basic overview of the system Contains only 1 process
given the number zero
Shows all external entities
Major data flows among entities
Generally no data stores
Assign a name to the whole system

10. Context DFD Examples Apartment Rental Receipts, Notices Lease External
Cash
Report
External
Manager
Apartment
Rental
System
Tenant
Lease,
Payments
Bank Deposit
Bank

11. Recall: on-line university registration (from Use Case examples)
The system should enable the staff of each academic department to examine the course offered by their department, add and remove course, and change the information about them (e.g., the maximum number of students). It should permit students to examine currently available courses, add and drop courses to and from their schedules, and examine the course for which they are enrolled. Department staff should be able to print a variety of reports about the courses and the students enrolled in them. They system should ensure that no student takes too many course and that students who have any unpaid fees are not permitted to register. (Assume that a fees data store is maintained by the university's financial office that the registration system accesses but does not change.)

12. Registration Context Diagram
Course
Registration
System
Course
information
Enrollment
information
Department
Staff
Students
Course
offerings
Student
schedules

13. Recall: real estate (from Use Case examples)
A Real Estate Inc. (AREI) sells houses. People who want to sell their houses sign a contract with AREI and provide information on their house. This information is kept in a database by AREI and a subset of this information is sent to the citywide multiple-listing service used by all real estate agents. AREI works with two types of potential buyers. Some buyers have an interest in one specific house. In this case, AREI prints information from its database, which the real estate agent uses to help show the house to the buyer (a process beyond the scope of the system to be modeled). Other buyers seek AREI’s advice in finding a house that meets their needs. In this case, the buyer completes a buyer information form that is entered into a buyer database, and AREI real estate agents use its information to search AREI’s database and the multiple-listing service for houses that meet their needs. The results of these searches are printed and used to help the real estate agent show houses to the buyer.

14. AREI Context Diagram AREI System Buyer information Sellers Buyers
Buyer
information
Sellers
Buyers
House
information
House
information
House
Information
House
Information
Multiple
Listing
Service

15. Level 0 DFD Detail from “exploding” the context-level DFD
Show less than 9 processes
Number each process
Show data stores (master files)
Ignore the handling of exceptions
Show all external entities

16. D1 Tenant File 1 Tenant Bank 2 Ext. Mgr 3 D1 Tenant File
Level 0 DFD: Apartment Rental
Tenant Info D1
Tenant File
Copy of lease 1
Lease
New
Tenant
Process
Tenant
Receipt
Bank
Deposit
Bank 2
Payments
Notice
Collection
Process
Cash Report
Unpaid
Charges
Tenant
Info
Ext.
Mgr 3 D1
Tenant File
Delinquent
Process
Delinquency
Report
Delinquencies

17. Level 0 DFD: Registration
Course Offering
Changes 1
Maintain
department
course
offerings
Available
course request
Available
courses
Available
courses
Course Offering
List 2
Maintain
student
enrollments
Students
Available courses
Course enrollment
Course
Offering
Updates
Course
Offerings
Student schedule
Course
enrollment
request D2
Course Offerings
Dept
Staff
Student
schedule
Course
information D3
Enrollments
Fee Payment
History
Student Enrollment
Report Request 3
Course
Enrollment
Reports D1
Fees
Enrollment
information
Student
Enrollment
Report

18. Level 0 DFD: AREI Sellers Maintain house seller information D2
Sales Contracts
House
Generate
requested
report 1 2
Sales Contract D3
Offered Houses
House information
Buyer information form D1
Multiple Listing
Services File
Sales
Contract
Buyers
House information request D4
Buyer

19. Create Child Diagrams Vertical Balancing
A child diagram cannot produce output or receive input that the parent does not produce or receive
External entities are not shown
May contain additional data stores
e.g.., transaction files
Primitive when no longer exploded

20. 2.1 Deposit Checks Deposit Receipts Bank Deposit D1 Tenant File
Level 1 DFD: Apartment Rental
2.1
Deposit Checks
Deposit Receipts
Collect
Security
Deposit
Tenant
Info
Bank Deposit D1
Tenant File
Tenant
Info
Bank Deposit
2.2
Rent Checks
Payment Receipts
Collect
Rent
Cash
Report
Unpaid
Charges

21. 2.1.1 Deposit Check 2.1.2 Update Info D1 Tenant File 2.1.3 Receipt
Level 2 DFD: Apartment Rental
2.1.1
Deposit
Check
Bank Deposit
Make
Bank
Deposit
Deposit
Info
2.1.2
Update
Info
Update
Tenant
File D1
Tenant File
2.1.3
Receipt
Create
Receipt
Tenant
Info

22. Level 1 DFD (1 of 3): Registration
Dept.
Staff
Produce
course
offering
list
Add new
Department ID D2
Course Offerings
Course to
delete
Course modifications
Course Offering
List Request
Course offering list
New Course
information
Delete
Modify
existing
courses
Course to delete
Existing Course
1.1
1.2
1.3
1.4

23. Level 1 DFD (2 of 3): Registration
Available Course
Request
Produce
course
offering
list
2.1
Available courses
Available
Courses D2
Course Offerings
Add course
to schedule
2.2
Course enrollment add
Course to add
to enrollment
Fee payment history D1
Fees
Students
Delete
course from
schedule
2.3
Course enrollment
add
Course to
delete
Course to delete D3
Enrollments
Obtain
current
schedule
2.4
Student enrollment
information
Current schedule request
Student schedule

24. Level 1 DFD (3 of 3): Registration
Dept.
Staff
Obtain
report
type D2
Course Offerings
Report
Course offering
information
Generate
requested
3.1
3.2
Request D3
Enrollments
Enrollment
Requested

25. Common Errors Forgetting data flows Arrow pointing wrong way
Connecting data stores & sources
Incorrectly labeling processes or flows
Too many processes (break it up!)
Data flows entering a process must be different when leaving!

26. Logical & Physical DFDs
focuses on modeling the business
system independent
Physical
focuses on modeling the system
system dependent

27. Logical DFDs - Current System
Good for communication & understanding
Focus on business activities
User view of the current system
Model of the business

28. Logical DFDs - New System
Look for improvements
effectiveness - i.e., doing the “right thing”
efficiency - i.e., doing the “thing right”
Transition from “Analysis” to “Design”

29. Physical DFDs Use the new logical DFD to make transition to a CBIS
Define Machine versus manual boundaries
processes = programs or manual procedures
data stores = data files or manual files
Define controls, validations, & security
Define actual file names & printouts
Master & transaction files

30. Partitioning the Physical DFD
Defining
manual procedures
automated procedures
circled using a dotted line
Batch versus On-Line Procedures

31. 2.1.1 Deposit Check 2.1.2 Update Info D1 Tenant File 2.1.3 Receipt
Bank Deposit
Make
Bank
Deposit
Deposit
Info
2.1.2
Update
Info
Update
Tenant
File D1
Tenant File
2.1.3
Receipt
Create
Receipt
Tenant
Info