SSADTools

&technique S

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PRESENTED BY

Management Information System

MIS is a system consisting of people, machines, procedures, databases and data models, as its elements.

The system gathers data from the internal and external sources of a organization, processes it and supplies information.

HISTORY OF SSAD

SSAD was introduced in 1981 as the standard method of analysis and design developed by CCTA (Central Computing and Telecommunications Agency) for UK Government projects

SSAD was made mandatory for all new information system developments in 1983

After a series of successful pilot implementation,the full implementation of SSAD commencedin 1991

HISTORY

Structured Systems Analysis and Design (SSAD) is an integrated set of standards and guides for the analysis and design of computer systems

It is an integrated set of standards and guidelines consisting of : Structural standards, which define the structure of a development project in the form of explicitly defined tasks, with clearly defined interfaces between them, and also the tangibleproducts

Structured Systems Analysis and Design

Improves productivity Improves flexibility Improves quality by reducing error rates Delivers the system to users on time Prevents IT developers’ bureaucracy Delivers systems that meets user's needs

Benefits Of SSAD

Disadvantages Of SSAD

The size of SSAD is a big hindrance to using it in all circumstances

There is a large investment in cost and time involved in training people to use the technique to come to terms with

There are lot of standards for the preparation and presentation of documents

Data Flow DiagramData DictionaryDecision TreeStructured EnglishDecision Table

Tools of SSAD

Data Flow Diagram Data Flow Diagram is a graphical

representation of the logical flow of the data.

It helps in expressing the system’s requirements in simple and understandable form

It is also known as a bubble chart.

Its aim is to clarify the system requirements and identify major transformations that will become programs in system design

It decomposes the requirement specifications down to the lowest level of details

DFD contains 4 graphic symbols for

Source/destination

Data flow

Process

Data store

Source/destination

Sign: Square.

Symbol:

Meaning: source/destination

Description: It represents source/destination

of system data.

Sign: Arrow

Symbol:

Meaning: Data Flow

Description : It identifies the data flow; it is a pipeline through which the data flows.

Data Flow

Sign: circle/ bubble

Symbol:

Meaning: Process

Description: It represents a process that transforms incoming data flow into outgoing flow.

Process

Sign: Rectangle

Symbol:

Meaning: Data store

Description:It represents data store.

Data store

Processes should be named and numbered

The direction of flow is from top to bottom from left to right

The name of the data stores, sources and destination is in capital letter.

Process and data flows name have the first letter capital

When a process is explored / divided in lower level they are number properly

Rules for constructing /drawing DFD

In case of payroll system to prepare salary statement for each employee data flow can be represented as-

Employee Data

Accounts Dept

Payroll processing

Salary statement

Employee file

Employee

Though DFD is very effective when required design is not clear and the user requires only graphic representation but more than 10-12 processes will make system complex and difficult to understand.

ADVANTAGE & DISADVANTAGE

Data Dictionary

A data dictionary is a structured repository of data. It is a set of rigorous definitions of all DFD data elements and data structure

It supports documentation in a better way

It serves as a common database for programmer and can be also used for control purposes

THERE ARE THREE CLASSES OF ITEMS TO BE DEFINED:

1. Data element - the smallest unit of data that provides for no further decomposition.

2. Data structure - a group of data elements handled as a unit

3. Data flows/stores - data flows are nothing but data structures in motion, whereas data stores are data structures at rest.

Rules for constructing Data Dictionary

The terms used to describe data structures are always in capital letters

Assigned names should be straightforward and user oriented

There should be names for every data flow, data store, data structure and data element

Consistency checks should be performed

Identification numbers of the process and their names should be mentioned in the data dictionary

STRUCTURED ENGLISH

Structured English aims at getting the benefits of both the programming logic and natural language

It uses logical construction and imperative sentences designed to carry out instructions for action

Decision are made through IF-THEN-ELSE statements

Its sentences should be precise, concise and clear in word and meaning

Example of Structured English

A bank will grant loan under the following conditions :

If a customer has an account with the bank and had no loan outstanding, loan will be granted

If a customer has an account with the bank but some amount is outstanding from previous loans then loan will be granted if special approval is given

Reject all loan applications in all other cases

IF customer has a Bank Account THEN IF Customer has no dues from previous account THEN Allow loan facility ELSE IF Management Approval is obtained THEN Allow loan facility ELSE Reject

DECISION TREE

Clear graphic representation of the logic, which looks like the branches of a tree, called decision tree

Easy to construct, read and update

Turns a decision table into a diagram & is read from left to right

Can be used to verify logic in problem that involves

few complex decisions.

Example: Computer dealer gets a trade discount of 35% if the order size is 6 or more PCs, whereas for orders from educational institutions and individuals, 15% discount is allowed on order of 6-19 PCs, 20% on orders for 20-49 PCs; 30% on orders for 50 PCs or more

Dealer 6 or more 35%

Less than 6 NIL DISCOUNT POLICY

Educational Institution or individual 50 or more 30%

20 – 49 20% 6-19 15% Less than 6 NIL

Decision tree

DECISION TABLE A matrix of rows and columns that shows

conditions and actions

Decision rules state the procedure to be followed when certain conditions exist.

Decision table are best-suited for dealing with complex branching routines, e.g., inventory control

A condition is usually given a value of 'Y' for 'Yes,

if is true", 'N' for 'No' and a dash for 'Do not care' in each rule.

Decision table consists of four sections. A condition stub at the upper left, a condition entry at the upper right, an action stub at the lower left, and an action entry at the lower right

Questions are listed in the condition stub and the action stub outlines the action to be taken to meet each condition

Condition entry part contains the answers to questions asked in the condition stub and the action entry part indicates the appropriate action

Condition Stub Condition Entry

Action Stub Action Entry

In constricting a decision table, the following rules are observed:

A decision should be given a name to be written at the top left of the table

The logic should be independent of the sequence in which the condition rules were written but the action takes place in the order in which the events occur

Consistent and standardized language should be used

Duplication of the terms should be avoided to the maximum extent

TECHNIQUES OF STRUCTURAL SYSTEM ANALYSIS AND DESIGN

Data Flow Modeling (DFM)

Logical Data Structure (LDS)

Entity Life History (ELH)

DATA FLOW MODELING

Pictorial representations of systems have long been acknowledged as being more effective than narrative Conventional flowcharts have been used for many years, with considerable advantages over narrativeHere are some examples: System flowchart (for high-level system description) Clerical procedure flowchart (for low-level description) Computer run chart

Disadvantages

They confuse the logical aspects of the system (what is done) with the specific physical implementation (how it is done)

They do not allow any easy transition from high-level broad description to detailed low-level description

They are "procedure orientated", placing the greatest emphasis on procedures in the system, rather than on data which appears only occasionally on the flow chart

LOGICAL DATA STRUCTURE:

The pictorial representation of entities and the relationships between them is called an Entity model

A current system Logical Data Structure (LDS) is a form of Entity model which represents entities and their relationships in the current system environment

EntitiesFor those unfamiliar with the term

"entity" its nearest equivalent in more familiar terminology is "file"

A working definition, suitable at this stage, is "something about which an organization keeps data"

An entity may be physical, e.g. Person, Building, Machine etc, or conceptual, e.g. Cost centre, project, etc.

ENTITY LIFE HISTORY Entity Life Histories (Elhs) look at a system from a third viewpoint, providing a means of representing how entities change within a system with the passage of time

Elhs start with the creation of an entity, record the sequence of changes which take place during its life within the system and end with its removal from the system

ELHS & PROCESSES

Elhs are used to help define : the logic associated with update

processes an examination of processes

provides a starting point to describe ELH concepts and terminology

ELHS are concerned with update processes only

Facilitate more focus on reducing maintenances and time effort in system development Integrate change when needed Widely useful in industry - proven techniques Part of career growth in IT - lots of interesting and well-paying jobs! Shows a steep increase in demand for systems analysis skills

CONCLUSION