1Lecture 8

Introduction to Systems Introduction to Systems AnalysisAnalysis

ObjectivesObjectives– Explain how systems analysis relates to business Explain how systems analysis relates to business

needs, problems, and opportunitiesneeds, problems, and opportunities– List and describe the types of system requirements List and describe the types of system requirements

that must be identified during systems analysisthat must be identified during systems analysis– Describe the symbols used in data flow diagrams Describe the symbols used in data flow diagrams

and explain the rules for their useand explain the rules for their use– Explain the sequence of data flow diagrams, from Explain the sequence of data flow diagrams, from

general to specific, and what each data flow general to specific, and what each data flow containscontains

– Draw a complete set of data flow diagrams for an Draw a complete set of data flow diagrams for an information systeminformation system

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Objectives of Systems AnalysisObjectives of Systems Analysis– Learn how the current system worksLearn how the current system works– Determine and document fully how Determine and document fully how

the system could work betterthe system could work better– Develop a logical model of the new Develop a logical model of the new

systemsystem– Make recommendations to Make recommendations to

managementmanagement

IntroductionIntroduction

3Lecture 8

Overview of the Systems Overview of the Systems AnalysisAnalysis

Systems analysis phase tasksSystems analysis phase tasks– Gather and record facts about the current Gather and record facts about the current

system and what is required to support system and what is required to support business needsbusiness needs

Three-step approach to decision-makingThree-step approach to decision-making– Determine the factsDetermine the facts– Analyze the factsAnalyze the facts– Make a decisionMake a decision

Two steps in the systems analysis phaseTwo steps in the systems analysis phase– Requirements determination (fact-finding)Requirements determination (fact-finding)– Requirements analysisRequirements analysis

4Lecture 8

The Challenge of Systems The Challenge of Systems AnalysisAnalysis

Requirements determination questionsRequirements determination questions– Who does it?Who does it?– What is done?What is done?– Where is it done?Where is it done?– When is it doneWhen is it done– How is it doneHow is it done

Another important questionAnother important question– Why? Why?

5Lecture 8

Fact-finding TechniquesFact-finding Techniques InterviewingInterviewing Documentation reviewDocumentation review ObservationObservation QuestionnairesQuestionnaires SamplingSampling ResearchResearch

6Lecture 8

The Challenge of Systems The Challenge of Systems AnalysisAnalysis

Requirements analysis questionsRequirements analysis questions– Who Who shouldshould do it? do it?– What What shouldshould be done? be done?– Where Where shouldshould it be done? it be done?– When When shouldshould it be done? it be done?– How How shouldshould it be done? it be done?

7Lecture 8

Systems RequirementsSystems Requirements Characteristics or features that must Characteristics or features that must

be included to satisfy business be included to satisfy business requirementsrequirements– Outputs Outputs – InputsInputs– ProcessesProcesses– TimingTiming– ControlsControls– Volumes. sizes, and frequenciesVolumes. sizes, and frequencies

8Lecture 8

Structured AnalysisStructured Analysis Examines inputs, outputs, and Examines inputs, outputs, and

processesprocesses Uses three main toolsUses three main tools

– Data flow diagrams (DFDs)Data flow diagrams (DFDs)– Data dictionaryData dictionary– Process descriptionsProcess descriptions

Tools can be applied using computer-Tools can be applied using computer-aided software engineering (CASE) aided software engineering (CASE) toolstools

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Data Flow DiagramsData Flow Diagrams Data flow diagrams (DFDs) are Data flow diagrams (DFDs) are

graphical aids that describe an graphical aids that describe an information systeminformation system

DFDs represent a logical model DFDs represent a logical model that shows that shows whatwhat a system does, a system does, not not howhow it does it it does it

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Data Flow DiagramsData Flow Diagrams Data flow diagram symbolsData flow diagram symbols

– Four basic symbolsFour basic symbols ProcessProcess Data flowData flow Data storeData store External entityExternal entity

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Data Flow DiagramsData Flow Diagrams– Process symbolProcess symbol

Symbol is a rectangle with rounded cornersSymbol is a rectangle with rounded corners Documented with process descriptionsDocumented with process descriptions Receive input data and produces outputReceive input data and produces output Output has a different form, or content, or Output has a different form, or content, or

bothboth Details are shown in a process description Details are shown in a process description In DFDs the process symbol appears as a In DFDs the process symbol appears as a

black box, underlying details not shownblack box, underlying details not shown

13Lecture 8

Data Flow DiagramsData Flow Diagrams– Data flow symbolData flow symbol

Symbol is a line with an arrowhead showing Symbol is a line with an arrowhead showing directiondirection

A path for data to move from one part of A path for data to move from one part of the system to anotherthe system to another

Might represent one or many pieces of dataMight represent one or many pieces of data At least one data flow must enter and exit At least one data flow must enter and exit

each processeach process

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15Lecture 8

Data Flow DiagramsData Flow Diagrams– Data flow symbolData flow symbol

Incorrect process and data flow Incorrect process and data flow combinations cause problemscombinations cause problems Spontaneous generation Spontaneous generation

(miracle)(miracle) Black holeBlack hole Gray hole Gray hole

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17Lecture 8

Data Flow DiagramsData Flow Diagrams– Data store symbolData store symbol

Symbol is a rectangle open on the right Symbol is a rectangle open on the right sideside

Data store also is called a data repositoryData store also is called a data repository Represents data that is retained for later Represents data that is retained for later

processingprocessing Must be connected to a process with a Must be connected to a process with a

data flowdata flow Must have at least one outgoing and Must have at least one outgoing and

incoming data flowincoming data flow

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Data Flow DiagramsData Flow Diagrams– External entity symbolExternal entity symbol

Symbol is a square, usually shadedSymbol is a square, usually shaded Represents a person, organization, or Represents a person, organization, or

other system that provides data or other system that provides data or receives output from the systemreceives output from the system

External entities are called terminatorsExternal entities are called terminatorsSource (supplies data to the Source (supplies data to the system)system)Sink (receives data from the Sink (receives data from the system)system)

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Data Flow DiagramsData Flow Diagrams Context diagramsContext diagrams

– Top-level view that shows the overall Top-level view that shows the overall boundaries of the systemboundaries of the system

– Represent the results of fact-findingRepresent the results of fact-finding– One process symbol, numbered 0 One process symbol, numbered 0

(zero) is drawn in the center(zero) is drawn in the center– Data flows connect the process to the Data flows connect the process to the

entitiesentities– Abbreviated symbols can be used to Abbreviated symbols can be used to

identify entitiesidentify entities

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Data Flow DiagramsData Flow Diagrams Conventions for data flow diagramsConventions for data flow diagrams

– Each context diagram must fit on one Each context diagram must fit on one pagepage

– Process name in the context diagram Process name in the context diagram should be the name of the information should be the name of the information systemsystem

– Use unique names within each set of Use unique names within each set of symbolssymbols

– Do not cross linesDo not cross lines– Use abbreviated identificationsUse abbreviated identifications– Use a unique reference number for each Use a unique reference number for each

process symbolprocess symbol

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Data Flow DiagramsData Flow Diagrams Lower-level diagramsLower-level diagrams

– Usually necessary to show more detailUsually necessary to show more detail– Design must considerDesign must consider

LevelingLeveling BalancingBalancing Data storesData stores

29Lecture 8

Data Flow DiagramsData Flow Diagrams– LevelingLeveling

Process of drawing increasingly detailed diagramsProcess of drawing increasingly detailed diagrams Also called exploding, partitioning, or decomposingAlso called exploding, partitioning, or decomposing

– BalancingBalancing Maintains consistency among an entire set of DFDsMaintains consistency among an entire set of DFDs Parent’s input and output data flows are preserved Parent’s input and output data flows are preserved

on the childon the child– Data storesData stores

Might not appear on higher-level DFDsMight not appear on higher-level DFDs Are shown on the the highest-level DFD that has Are shown on the the highest-level DFD that has

two or more processes using that data storetwo or more processes using that data store

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