Structuring User Requirements

IS 592Dr. Dania BilalSpring 2005

Recap of Systems Analysis Phase

Determining user requirements Structuring user requirements Selecting the best system design

strategy

Structuring User Requirements

Data Flow Diagrams (DFDs) Analysis tool to structure user

requirements in a system Graphically represents data movement

or flow in an information system and relationships among data flow

DFDs

Show the processes that transform or change data

Focus on movement of data between processes ->DFDs are called process models Process modeling shows data flow through

the system based on an organization’s rules, decisions, and policies

DFDs

Increase software development productivity by avoiding mistakes in representing user requirements

Saving money in software cost

Based on user requirements gathered during planning stage

Evolve from the more general to the more specific

DFDs

DFDs of current system Used to understand current system

DFDs of new logical system Used to show data flow, structure, and

functional requirements of new system

DFDs Symbols

Flow of data is represented by Data flow Data Store Process Source (external entities)

DFDs Symbols

Data Flow Data in motion from one place in a

system to another Example: user query in a database

DFDs Symbols

Data store Physical location or various locations of

data in an information system Example: a data store in a circulation

system contains data about students, faculty, staff, community users, etc.

DFDs Symbols

Process Actions performed on data for

transformation, storage, and distribution May represent data in

File folder, computer-based file, notebook

DFDs Symbols

Source/sink Depicts the origin and/or destination of

data Referred to a external entity

Another organization or unit that sends and receives information from the system

A person who interacts with the system, inside or outside

Another information system that exchanges information with the system under analysis

DFDs Symbols

Source/sink Defines the system boundaries Data originates outside a system from

one or more sources, and the system produces information to one or more sinks

DFD Mechanics

How the four symbols are represented? Data flow: drawn as an arrow Data store: drawn as a rectangular Process: drawn as a circle Source/sink: drawn as a square

DFD Definitions Level-0 diagram

Represents a system’s major processes, data flow, and data stores at the highest level of detail

Context diagram Shows major flow between entities and

the system (too general) Level-N diagram

A DFD that results from a decomposed Level-0 diagram

Types of DFDs

Current logical Depicts current system

New logical Has additional functions Inefficient data flows are reorganized

New physical Depicts physical implementation of the

new system

DFDs

Examples Visit

http://www.umsl.edu/~sauter/analysis/dfd/dfd.htm

For additional information or clarification Visit

http://management.wcupa.edu/mis451/chapter08.ppt#256,1,Slide 1