structured development

8/14/2019 Structured Development

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Structured

Systems Analysis


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Managing Requirements

Text requirements can be extractedfrom diagrams.

The diagram structure can also beused to organize text requirements.

Be sure to create traceability fromdiagrams to text requirements


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Data flow diagrams

Depict the flow of data and itstransformation. Throughdecomposition, greater detail is

revealed and documented in layers ofDFDs.

A numbering system is used to

hierarchically relate the processlayers.

Data stores are also numbered so theycan be traced to data models.

There are four diagram components:


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Processes

have at least one input and oneoutput.

The process is usually symbolized by

a "bubble" or similar figure. The process is what transforms the

data. Functional primitives are at

the lowest level of the DFDs andcan be decomposed no further. Youknow you have gone past thefunctional primitive when the result

sounds like program logic (if, then;


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Data stores

are used to represent data structuresor logical data files. They areoften represented as open-ended

shapes.


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External entities

Represent interfaces external to thesystem. These are oftenrepresented as a small shape, such

as a diamond. Eg Suppliers, Customers


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Data flows

represent the exchange of databetween processes, processes anddata stores, and processes and

external entities. The direction of the data flow defines

how data flows through the system.

Data flow direction is represented byarrows.


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dataflow diagram

one of the three major graphicalmodeling tools of structuredanalysis:

The dataflow diagram is a modelingtool that allows us topicture asystem as a network of

functional processes, connectedto one another by pipelines andholding tanks of data.


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synonyms for dataflowdiagram:

Bubble chart

DFD

Bubble diagram Process model (or business process

model)

A picture of whats going on aroundhere


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The dataflow diagram

one of the most commonly usedsystems-modeling tools, particularlyfor operational systems in which thefunctions of the system are ofparamount importance and morecomplex than the data that thesystem manipulates.

Notation had been borrowed fromearlier papers on graph theory, andit continues to be used as aconvenient notation by software

engineers concerned with directim lementation ofmodels of user


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In the above example .

all the requirements belong under theparent 1.4.3.3: The system shallprocesspayment returns and

adjustments (in a separate DFD, notshown).

The parent is compound and should be

reworded. However, if you have limited resources,

focus on the functional primitivesbecause they are critical to the

subsequent development phases.


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In backward traceability, if all thechildren are satisfied, thecompound parent will be satisfied--

if all of the parent is planned forimplementation at the same timeduring the project.

If it is not, you will have traceabilityproblems.


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Structured Analysis


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Tom deMarco


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Data Flow Modeling

This is the process ofidentifying,modeling and documenting howdata moves aroundan information

system.

Data Flow Modeling examinesprocesses (activities that transform

data from one form to another), datastores (the holding areas for data),external entities (what sends datainto a system or receives data from a

system), and data flows (routes by

Analysis of the current


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Analysis of the currentsystem

Also known as: feasibility stage.

Analyze the current situation at ahigh level.

A Data Flow Diagram (DFD) is usedto describe how the current systemworks and to visualize known

problems.
http://en.wikipedia.org/wiki/Data_Flow_Diagramhttp://en.wikipedia.org/wiki/Data_Flow_Diagram


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Investigate currentprocessing

It investigates the information flowassociated with the servicescurrently provided, and describes

them in the form of Data FlowModel.

At this point, the Data Flow

Model represents the currentservices with all theirdeficiencies.

No attempt is made to incorporate


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Appropriate ProcessName


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Data Store


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External Entity


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Process Names

CALCULATE MISSILE TRAJECTORY

PRODUCE INVENTORY REPORT VALIDATE PHONE NUMBER

ASSIGN STUDENTS TO CLASS


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Process Names ?

DO STUFF

MISCELLANEOUS FUNCTIONS

NON-MISCELLANEOUS FUNCTIONS

HANDLE INPUT

TAKE CARE OF CUSTOMERS

PROCESS DATA GENERAL EDIT


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Process Names to avoid

DO STUFF

MISCELLANEOUS FUNCTIONS

NON-MISCELLANEOUS FUNCTIONS

HANDLE INPUT

TAKE CARE OF CUSTOMERS

PROCESS DATA GENERAL EDIT


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Logical Data Modeling

This is the process ofidentifying,modeling and documenting thedata requirements of the system

being designed.

The data are separated into entities

(things about which a businessneeds to record information) andrelationships (the associations

between the entities).


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Entity RelationshipDiagram

Entity Relationship Diagram is aspecialized graphic that illustrates

the interrelationships betweenentities in a database.

i l i hi


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Entity RelationshipDiagram

| One-to-one Relationship ]

[ One-to-many Relationship

| Many-to-many Relationship
http://www.visual-paradigm.com/VPGallery/datamodeling/OneToOneRelationship.htmlhttp://www.visual-paradigm.com/VPGallery/datamodeling/OneToManyRelationship.htmlhttp://www.visual-paradigm.com/VPGallery/datamodeling/ManyToManyRelationship.htmlhttp://www.visual-paradigm.com/VPGallery/datamodeling/ManyToManyRelationship.htmlhttp://www.visual-paradigm.com/VPGallery/datamodeling/OneToManyRelationship.htmlhttp://www.visual-paradigm.com/VPGallery/datamodeling/OneToOneRelationship.html


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Flowchart vs. Data FlowDiagram (DFD)

My employer asked me to create a flowchart inthe submission of list of on-going classes(LOGC). I decided to use a data flow diagram(DFD) instead of a flowchart. When I presentedmy work, she liked my diagram but she

preferred a flowchart rather than a DFD.I thought it was just a communication problem.However, I realized that using a DFD indescribing processes was easier to

understandcompared to flowcharts.What do you think? Are flowcharts obsolete?Posted: 07/09/2008 @ 06:05 AM (PDT) TechRepublic Blog

l h diff f


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Flowchart differs from DataFlow Diagram -

Flowchart: using it when you want todescribe steps of process done insequence.

Data Flow Diagram: using it when youwant to describe the relations andprocess between data, actions.

So Flowchart and DFD have differentmeaning and used in different ways.

Posted: 07/23/2008 @ 06:39 AM (PDT)

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