structured system analysis and design

8/7/2019 Structured system analysis and design

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Contents

What Is Structured Analysis?

Tools Used for Structured Analysis.

Data Flow Diagram.

Data Dictionary.

Structured English.

Decision Tree.

Decision Table.


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What is structured analysis

Structured Analysis is a set of techniques andgraphical tool that allow the analyst todevelop a new kind of system specifications

that are easily understandable to the user.

Are methods for analyzing and convertingbusiness requirements into specifications and

ultimately, computer programs, hardwareconfigurations and related manualprocedures.


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The analysis consists of interpreting the

system concept into data and control

terminology.

Is part of a series of structured methods,

that "represent a collection of analysis,

design, and programming techniques that

were developed in response to the problemsfacing the software.


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Tools Used for Structured Analysis

Data Flow Diagram (DFD)

Data Dictionary.

Structured English.

Decision Tree.

Decision Table


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Data Flow Diagram (DFD)

A Data Flow Diagram (DFD) is a graphicalrepresentation designed by a system analyst and isused as a reference point by the programmer whichportrays the "flow" of data through an informationsystem.

It is a starting point of the design phase thatfunctionally decomposes the requirementsspecifications down to the lowest level of detail.

It is primarily used for the visualization of dataprocessing for the structured design of an informationsystem.

DFD consists of a series of bubbles joined by lines.The bubbles represent data transformations and the

lines represent data flows in the system.


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This is also called a bubble chart.

It has four symbols: Square (defines sources), arrow (definesdata flow), circle (defines process) and open rectangle

(defines data store).

It is the starting point in the system design that decomposes

requirements to the lowest level of detail.

It identifies major transformations that eventually become

programs in system design.

It consists of a series of bubbles joined by lines. Bubblesrepresent transformations and the lines represent the data

flows in the system.


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Advantages

Represents data flows.

May be used at high or low level of analysis. Forinstance, if the DRE is low during analysis and

design, it means you should spend timeimproving the way you conduct formal technicalreviews.

Provides good system documentation.

Process bubbles can be hierarchicallydecomposed into sub-DFDs; the inputs andoutputs must match at all levels ofdecomposition, so the design has validation.


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DataDictionary A Data Dictionary is a structured repository of data about

data.

It is a set of rigorous definitions of all DFD data elementsand data structures.

It clearly documents the list of contents of all data flows,

processes and data stores. The three classes to be definedare:

1.Data Elements: - this is the smallest unit of data. Furtherdecomposition is not possible.

2.Data Structure: - this is a group of Data Elements which

together form as a unit in a data structure.3.Data flows and Data stores: - data flows are data structures

in motion. Data Stores are data structures in store. (Datastructures in a data store - a data store is a location wheredata structures are temporarily located.)


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Structured English

It uses logical constructs to carry out

instructions for actions.

Decision are made through the use of IF,THEN, ELSE and SO statements.

It is highly correlated to the decision tree.

It would not be a misnomer to call it the

pseudo code of the program.


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Decision Tree

These clearly sketch out the logical structure

based on the stated policy.

It is easy to construct , easy to read and easyto update.

It shows only the skeletal aspects of the

policy, however in the sense that it does not

lend itself to calculations or show logic as aset of instructions for action.


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Decision Table

A decision table is a table of contingencies

for defining a problem and the actions that

need to be taken for it.

It is a single representation of therelationships between conditions and

actions; these pairs of condition sets and

actions sets are known as rules

A condition is usually given a value of 'Y' for'Yes, it is true", 'N' for 'No' and a dash for 'Do

not care' in each rule.


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Decision table wins over a decision tree thatit can clearly call out the conditions that

need to be tested.

Decision table can be used to generate code

in a procedural application language which is

optimized for performance based on the

expected likelihood of a rule being valid in

the data.


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Conclusion

DFD- The primary strength is its ability to representdataflow. However, the tool only weakly shows input and

output detail.

DataDictionary- It helps the analyst to simplify the

structure for meeting the data requirements of thesystem, but it does not provide functional details.

Structured English- It is best used when the problemrequires sequences of actions with decisions.

Decision Tree- These are used to verify logic and in

problems that involve a few complex decisions resulting ina limited no of actions.

Decision Table- Best suited for dealing with complexbranching routines such as calculating discounts or sales

commissions or inventory control procedures.


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