Managing Information Systems (Data Flow

Diagrams) Enterprise & Project Management

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Please note that these slides are not intended as a substitute

to reading the recommended text for this course.

Explain the purpose of DFDs

Construct DFDs

Discuss the Advantages of DFDs

Debate some of the issues in relation to DFDs

Objectives

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A data flow diagram (DFD) is a graphical tool that allows system analysts (and system users) to depict the flow of data in an information system.

The DFD is one of the methods that system analysts use to collect information necessary to determine information system requirements.

What is a Data Flow Diagram?

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A Data Flow Diagram is intended to serve as a communication tool among

– systems analysts

– end users

– database designers

– system programmers

– other members of the project team

What is a Data Flow Diagram?

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Context Diagram

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Context diagram of a food ordering system

DFD have multiple layers / levels

– Level 0 – high level major processes, data flows, and data stores

– Subsequent levels (1,2,3…) – provide detail

Developing DFDs

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Level-0 Diagram

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Level-0 DFD of a food-ordering

system

E-Commerce Application: Process Modeling using DFD

7 Level-0 data flow diagram for the a Web store

Symbol Signifies

A data flow

External entity symbol

Process symbol

Data store symbol

DFD Symbols

Customer

2 Sales Desk

Enter new customer order

M2 Mailing List

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Data flow: arrows depicting movement of data

External entity: is a source or destination of a data flow which is outside / interface with the system.

Process: work or actions performed on data (inside the system)

Data store: data at rest (inside the system)

Definitions and Symbols

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1. Create a rough draft

2. Identify key data flows

3. Identify processes and data stores

4. Check for completeness

5. Establish level of detail

6. Review with users

Six steps in Constructing of a Level 1 DFD

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Note that a DFD is NOT time-sensitive, and that it is NOT a flowchart. It simply defines the functions of the system.

Four advantages over narrative explanations of data movement

– Easy to draw and amend

– Understanding of the interrelationships of systems and subsystems

– Communicating current system knowledge to users

– Analysis of the proposed system

However, there is a tendency to get ‘lost in the detail’ and confuse users.

Pros and Cons of Building a DFD

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DFD should allow:

– User manager to confirm the boundaries and scope are correct.

– System analyst to understand the present system and identify alternative solutions. Also provides evidence of what and how it is done.

– Project manger to assign team member to the task of building / implementing the solution

Different perspectives

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