SDLC Phase II: Structuring SDLC Phase II: Structuring System RequirementsSystem Requirements

IS 582IS 582

Dr. Dania BilalDr. Dania Bilal

Spring 2008Spring 2008

Last Week: SDLC Phase II Last Week: SDLC Phase II

Determining user requirementsDetermining user requirementsStructuring RFP based on gathered specifications Structuring RFP based on gathered specifications of user needsof user needs

– Wrote specifications for certain functionsWrote specifications for certain functions– Presented written specifications in classPresented written specifications in class

This Week: SDLC Phase II This Week: SDLC Phase II continuedcontinued

Structuring system requirementsStructuring system requirements

Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)– Analysis tool to structure user requirements in Analysis tool to structure user requirements in

a systema system– Graphically represents data movement or flow Graphically represents data movement or flow

in an information system and relationships in an information system and relationships among data flowamong data flow

DFDsDFDs

Show the processes that transform or Show the processes that transform or change datachange data

Focus on movement of data between Focus on movement of data between processes processes

DFDs are called process modelsDFDs are called process models

– Process modeling shows data flow through the Process modeling shows data flow through the system based on an organization’s rules, system based on an organization’s rules, decisions, and policiesdecisions, and policies

DFDsDFDs

Increase software development Increase software development productivity byproductivity by– avoiding mistakes in representing user requirementsavoiding mistakes in representing user requirements

Saving money in software costSaving money in software cost

Based on user requirements gathered Based on user requirements gathered during planning stageduring planning stage

Evolve from the more general to the more Evolve from the more general to the more specificspecific

DFDsDFDs

DFDs of current systemDFDs of current system– Used to understand current systemUsed to understand current system

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

functional requirements of new systemfunctional requirements of new system

DFDs SymbolsDFDs Symbols

Flow of data is represented byFlow of data is represented by– Data flowData flow– Data StoreData Store– ProcessProcess– Source (external entities)Source (external entities)

DFDs SymbolsDFDs Symbols

Data FlowData Flow– Data in motion from one place in a system to Data in motion from one place in a system to

anotheranother

ExamplesExamples– user query in a databaseuser query in a database– Other examples???Other examples???

DFDs SymbolsDFDs Symbols

Data storeData store– Physical location or various locations of data Physical location or various locations of data

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

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

DFDs SymbolsDFDs Symbols

ProcessProcess– Actions performed on data for transformation, Actions performed on data for transformation,

storage, and distributionstorage, and distribution– May represent data in May represent data in

File folder, notebookFile folder, notebook

DFDs SymbolsDFDs Symbols

Source/sinkSource/sink– Depicts the origin and/or destination of dataDepicts the origin and/or destination of data– Refers to a external entityRefers to a external entity

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

A person who interacts with the system, inside or outsideA person who interacts with the system, inside or outside

Another information system that exchanges information Another information system that exchanges information with the system under analysiswith the system under analysis

DFDs SymbolsDFDs Symbols

Source/sinkSource/sink– Defines the system boundariesDefines the system boundaries– Data originates outside a system from one or Data originates outside a system from one or

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

DFD MechanicsDFD Mechanics

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

DFD DefinitionsDFD Definitions

Level - 0 diagramLevel - 0 diagram– Represents a system’s major processes, data flow, Represents a system’s major processes, data flow,

and data stores at the and data stores at the highest level of detailhighest level of detail

Context diagramContext diagram– Shows Shows majormajor flow between entities and the system flow between entities and the system

(too general)(too general)

Level N diagramLevel N diagram– A DFD that results from a decomposed Level-0 A DFD that results from a decomposed Level-0

diagramdiagram

Types of DFDsTypes of DFDs

Current logicalCurrent logical– Depicts current systemDepicts current system

New logicalNew logical– Has additional functionsHas additional functions– Inefficient data flows are reorganizedInefficient data flows are reorganized

DFDsDFDs

New physicalNew physical– Depicts physical implementation of the new Depicts physical implementation of the new

systemsystem

ExamplesExamples– Visit Visit

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

Group or Individual Class ActivityGroup or Individual Class Activity

Do a Level 0 DFD for an automation Do a Level 0 DFD for an automation function that is of interest to you using function that is of interest to you using adequate symbols. You may use a adequate symbols. You may use a drawing software to perform this activity.drawing software to perform this activity.

Do a Level N DFD based on Level 0 Do a Level N DFD based on Level 0 diagramdiagram