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

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

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

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

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

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

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

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

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

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

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

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 1.1.1 and 1.1.2 In flowcharts, numbers are used for on- and off-page connectors ACCOUNTING INFORMATION SYSTEMS BASIC CONCEPTS & CURRENT ISSUES

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

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

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

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

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

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

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

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