1. Chapter 6 Data flow diagramming ACCOUNTING INFORMATION SYSTEMS
McGraw-Hill/Irwin
Accounting Information Systems
© 2008 The McGraw-Hill Companies, Inc. All rights reserved.
Chapter 6
Data flow diagramming
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

2. Outline Objectives DFD symbols DFD design conventions
Comparison with flowcharts
Database design
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

3. Objectives
When you finish studying this chapter, you should be able to:
Explain the symbols and design considerations associated with DFDs
Compare and contrast flowcharts and DFDs with regard to purpose, content, structure and use in AIS
Discuss ways DFDs are used in AIS work
Construct a leveled set of DFDs
Design normalized database tables from a DFD
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

4. DFD symbols
Processes are labeled with verb phrases, like “prepare sales invoice”
External entities are labeled with noun phrases, like “vendor”
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

5. Data flows are labeled with noun phrases like “remittance advice”
DFD symbols
Data flows are labeled with noun phrases like “remittance advice”
Data stores are labeled with noun phrases, like “accounts payable master file”
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

6. DFD design conventions
All processes should have unique names
The inputs to a process should differ from the outputs to a process
Any single DFD should not have more than about seven processes
No process can have only outputs
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

7. DFD design conventions
No process can have only inputs
A process has a verb phrase label
Data must be moved by a process from one data store to another data store
Data cannot move directly from an external entity to a data store
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

8. DFD design conventions
Data must be moved by a process to an external entity from a data store
A data store has a noun phrase label
Data of any concern to the system cannot move directly between external entities
An external entity has a noun phrase label
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

9. DFD design conventions
A data flow has only one direction between symbols
A data flow cannot go directly back to the same process it leaves
A data flow can go directly into a data store
A data flow has a noun phrase label
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

10. Comparison with flowcharts
Symbols
DFDs have four: circles, rectangles, lines and parallel lines
Flowcharts have many, including rectangles, diamonds and triangles
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

11. Comparison with flowcharts
Organization
DFDs are in leveled sets, each depicting more detail than the previous level
Flowcharts are organized in columns which depict areas of responsibility, such as departments
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

12. Comparison with flowcharts
Numbers
In DFDs, processes are numbered based on their level. Process 1.0 can lead to Processes 1.1 and 1.2; Process 1.1 can lead to Processes and 1.1.2
In flowcharts, numbers are used for on- and off-page connectors
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

13. Comparison with flowcharts
Focus
DFDs focus on data and how it moves between elements of an information system
Flowcharts are concerned with data, but also with documents and processing tools
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

14. Comparison with flowcharts
Use of lines
In a data flow diagram, lines represent data. They are labeled with noun phrases
In a flowchart, lines represent movement between processes, areas of responsibility and the like. They are not labeled
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

15. Database design Fundamental design element: the table
Rows are “records”
Columns are “fields”
A record usually comprises many fields
A field captures a single information item, like a date, last name or invoice number
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

16. Database design
Keys
Each record is uniquely identified by its primary key.
Student ID number
Textbook ISBN
If a single field alone won’t suffice, a table can have a compound primary key.
Last name and first name
Department, course code and section
A foreign key is a primary key that appears in another table.
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

17. Database design Other design elements
Queries: sets of instructions for retrieving data, performing calculations and other tasks
Display all sales invoice numbers from January 1 to January 15
Calculate the total amount due from customers whose last names start with “C”
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

18. Database design Other design elements
Forms: used for entering and looking up data
Order forms on the Internet
Looking up class schedules on your school’s information system
Reports: used to display data
Do not store derivable data in a table.
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

19. Database design Data normalization
The set of rules used to ensure that databases are as efficient and effective as possible
Minimize database size, optimize table design and access data more quickly and efficiently
Six normal forms exist; the first three are usually enough for business applications
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES

20. Database design Data normalization
1st normal form (1NF): eliminate repeating groups
2nd normal form (2NF): eliminate repeating groups AND eliminate redundant data
3rd normal form (3NF); eliminate repeating groups, redundant data AND columns not dependent on primary key
ACCOUNTING INFORMATION SYSTEMS
BASIC CONCEPTS & CURRENT ISSUES