SSADM Steps

Structure SystemsStructure Systems Analysis & Design

Prof P KarthikeyanAssistant Professor Senior

Analysis & DesignAssistant Professor. Senior

What is SSA & SD ?What is SSA & SD ?Composite of two separate but related p ptechniques.First is Structured System Analysis,First is Structured System Analysis,which is concerned with the modeling ofproblem-related features of a system,p ob e e ated eatu es o a syste ,making use of a set of descriptive formsthat can also be used for architecturala ca a so be used o a c ec u adesignThe second is Structured Design whichThe second is Structured Design whichin turn is oriented towards the solution-related aspects

Structured Systems Analysis and Structured Design

The Structured Systems Analysis - SSA techniques are centered on the use of the Data-Flow Diagram, or DFD, while the Structure Design – SD process makes use of the Structure Chart.

I Representation forms for SSA/SDI. Representation forms for SSA/SD1. Representations for structured systems analysis2. Representations used for structured design p gII. The SSA/SD Process1. Structure system analysis2. Transaction Analysis3. Transform Analysis4. Completing the design Process

I. Representation forms for SSA/SDRepresentations for structured systems analysis

The Structured Systems Analysis techniques are

centered on the use of the Data Flow Diagram, or

DFD.

DFDs provide a problem-oriented and functional

viewpoint that does not involve making any

assumptions about ‘hierarchy’.

The techniques of Structured Systems Analysis guide

the designer in building a model of the problem bythe designer in building a model of the problem by

using DFDs, elaborating this where necessary by

The functional viewpoint provided through the use of

DFDs can be augmented by means of more detailed

descriptions in the form of ‘process specifications’ or

‘P-Specs’(mini specs).

A P Spec is a textual description of the primitiveA P-Spec is a textual description of the primitive

process that is represented by a bubble in a DFD, and

so can be regarded as a subsidiary functional

viewpoint.

A typical P-Spec will summarize the process in terms

of its title a description of the input/output data flowof its title, a description of the input/output data flow

relating to the process, and the procedural tasks that it

performs couched in terms of the basic concepts of

Representations for structured systems analysis

. P-Spec number corresponds to

3.2.1 Cash Withdrawal

P Spec number corresponds to bubble id-number P-Spec title

/* customer selected ‘withdraw cash’ option */1. Prompt customer to select from ‘receipt’

option.2. If ‘receipt required’ selected 2.1.set ‘provide receipt’ flag

3. ……4….

Numbered steps (for easier reference)

Data dictionary:used to record the information content of data flowsused to record the information content of data flows.

This typically included descriptions of all of the data

forms that are mentioned in the DFDs, P-Specs and

any other forms of description that might be used.

The initial description provided by the data dictionary

h ld b hi hl b t t d h ld t fshould be highly abstract, and should not focus upon

physical format.

More recent developments in design practice

encourage the analyst to develop a set of ERDs as aencourage the analyst to develop a set of ERDs as a

means of modeling the relationships between the data

ConventionsFor clarity the use of the following operators is helpful:For clarity the use of the following operators is helpful:= means ‘is’ or ‘is equivalent to’.+ means AND+ means AND[] means either/OR, so that one of the enclosed options

will be selected{} means the components inside the braces are iterated( ) means that the component is optional( ) p pExamplesCustomer-id = bank code + sort code + account

numberAccount summary = account number + (withdrawal

amount) + {transaction log entries} + [withdraw |withdraw receipt | accnt summary ]

Representations used for structured design

I i ith th i t f f th tIn comparison with the variety of forms that can

be used for

the task of analyzing the structure of a problem,

the Structured Design activities mostly make use

of only one significant form of diagrammaticaly g g

notation.

As might be expected, the view point adopted is a

constructional one, and it is provided by the, p y

Structure Chart.

It is chiefly concerned with describing theIt is chiefly concerned with describing the

functions of the subprograms that make up a

program, together with the run-time invocation

hierarchy that links themhierarchy that links them.

It is therefore the task of the Structured Design

part of the method to bridge the gap between the

very different viewpoint and forms that are usedvery different viewpoint and forms that are used

for structured systems analysis and for

structured design, and the next section

provides an outline of the way in which this is

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Simple example of Structure Chart

SSA/SD ProcessBasic 5 steps:p

1. Construct an initial DFD to provide a top-leveldescription of the problem (the context diagram).

2. Elaborate this into a layered hierarchy of DFDs,supported by a data dictionary.

3 Use transaction analysis to divide the DFD into3. Use transaction analysis to divide the DFD intotractable units

4. Perform a Transform Analysis on the DFD created foreach transaction, in order to produce a StructureChart for the transaction.

5 Merge the resulting structure charts to create the5. Merge the resulting structure charts to create thebasic implementation plans, and refine them toinclude any necessary error-handling, initialization ,

d th tiand other exceptions.

Transformation Diagram for Structured Systems Analysis and Structured Designy g

Requirement Document

1. Construct initial DFD

Transformation of viewpoint (Creation

of model)

Data Flow Diagram

2. Refine DFD and

dRefinement of

viewpoint

Data Flow

expand viewpoint

Diagrams

3. Refinement ofTransaction Analysis

Refinement of viewpoint

4

Data Flow DiagramsOptionally add

central transform Transformation of4.

Transform Analysis

transform Transformation of viewpoint (add decisions about

invocation)

Structure Chart

5. Merge and Refine

Refinement of viewpoint

Structure Chart

Requirements document

1. Construct initial DFD – Transformation of viewpoint(creation of

model)

Data flow diagram

2. Refine DFD and Expand – Elaboration of view point

Data flow diagram

3. Transaction Analysis – Elaboration of view pointOptionally add central transform

Data flow diagrams

4. Transform Analysis – Transformation of view point( add

d i i b t i ti )decisions about invocation)

Structure charts

5 M d fi5. Merge and refine

Structure Chart

Step 1 and 2 : Structured System Analysis

• Level 0 = context diagram.

• Level 1 = top level DFD.

• Level 2 = explosion of level 1 DFD bubbles• Level 2 = explosion of level 1 DFD bubbles.

• Level 3 = use this level as appropriate.

Step 3: The transaction analysis step and has five basic components:basic components:

• The event in the systems environment that causes the transaction to occur;;

• The stimulus that is applied to the system to inform it about the event;

• The activity that is performed by the system as a result of the stimulus;Th th t thi t i t f t t• The response that this generates in terms of output from the system;

• The effect that this has upon the environment;• The effect that this has upon the environment;

Step 4: Identify the central transform in the DFD:

You do not have to redraw the DFDs but if you add a

“boss” bubble redraw showing where the boss fits.

Which will allow you to develop a hierarchical structure y p

chart. Develop structure charts for all of your level 1-2

DFDDFDs.

Step 5: Merge the Structure Charts

The objective of this step is to produce a single structure chart

Constructing SSA & SD for SafeHome security Co s uc g SS & S o Sa e o e secu ysystem

Context Diagram : Single BubbleCo e ag a S g e ubb e

Step 3: Transform Analysis

Step 4: Identify the central transform in the DFD:

Step 4: Identify the central transform in the DFD:

Step 4: Identify the central transform in the DFD:

Step 4: Identify the central transform in the DFD:

Step 4: Identify the central transform in the DFD:

Step 5: M th St t Ch tMerge the Structure Charts