Learning Material_System Analysis and Design

System Analysis and Design Syllabus

SYSTEM ANALYSIS AND DESIGN Module 1: Data and Information (3) Types of information: operational, tactical, strategic and statutory why do we need information systems management structure requirements of information at different levels of management functional allocation of management requirements of information for various functions qualities of information small case study.

Module 2: Systems Analysis and Design Life Cycle (3) Requirements determination requirements specifications feasibility analysis final specifications hardware and software study system design system implementation system evaluation system modification. Role of systems analyst attributes of a systems analyst tools used in system analysis

Module 3: Information gathering (3) Strategies methods case study documenting study system requirements specification from narratives of requirements to classification of requirements as strategic, tactical, operational and statutory. Example case study

Module 4: Feasibility analysis (3) Deciding project goals examining alternative solutions cost benefit analysis quantifications of costs and benefits payback period system proposal preparation for managements parts and documentation of a proposal tools for prototype creation

Module 5: Tools for systems analysts (3) Data flow diagrams case study for use of DFD, good conventions leveling of DFDs leveling rules logical and physical DFDs software tools to create DFDs

Module 6: Structured systems analysis and design (3) Procedure specifications in structured English examples and cases decision tables for complex logical specifications specification oriented design vs procedure oriented design

Module 7: Data oriented systems design (3) Entity relationship model E-R diagrams relationships cardinality and participation normalizing relations various normal forms and their need some examples of relational data base design.

Module 8: Data input methods (3) Coding techniques requirements of coding schemes error detection of codes validating input data input data controls interactive data input

Module 9: Designing outputs (2) Output devices designing output reports screen design graphical user interfaces interactive I/O on terminals.

V.Rajaraman/IISc, Bangalore V1/1-6-04/1


Module 10: Object oriented systems modeling (4) What are objects? Why objects? Objects and their properties classes inheritance polymorphism how to identify objects in an application how to model systems using objects some cases of object oriented system modeling

Module 11: Control audit and security of information systems (4) Audit and security of information systems why controls are needed objectives of control techniques used in control auditing information systems auditing around, through and with the computer testing information systems types of tests how to generate tests security of information systems disaster recovery business process continuity

Module 12: Systems analysis and design in the era of electronic commerce (3) B2B, B2C and C2C e-commerce advantages and disadvantages of e-commerce. E-commerce system architecture physical networks, logical network, World Wide Web, web-services html, XML.

Module 13: Electronic data interchange (2) EDI standards virtual private networks XML and EDI.

Module 14: Security of e-commerce transactions, firewalls (3) Encryption methods symmetric and asymmetric encryption digital signature certifying authorities for signatures legal status of e-commerce transactions

Module 15: Payment systems in e-commerce (2) Cheque payment, credit card payments, e-cash payments.

Module 16: Complete system analysis and design case studies (5) A system for journal acquisition in libraries walk through the entire life cycle



Lecture Plan

Hours Total Modules Learning Units per topic Hours

1. Data and 1. Types of information: operational, tactical, 0.5 Information strategic and statutory

2. Why do we need information systems, management structure, requirements of information at different levels of management

1 3

3. Functional allocation of management, requirements of information for various functions

1

4. Qualities of information small case study 0.5 2. Systems 5. Systems Analysis and Design life Cycle: Analysis and Requirements determination, requirements 1 Design Life specifications 3 Cycle 6. Feasibility analysis, final specifications,

hardware and software study, system design, system implementation, system evaluation, system modification.

1

7. Role of systems analyst attributes of a 1 systems analyst tools used in system analysis

3. Information 8. Information gathering, strategies, methods 1

3 gathering 9. Case study/documenting study, system

requirements specification, from narratives of requirements to classification of requirements 2 as strategic, tactical, operational and statutory. Example case study

4. Feasibility 10. How to formulate project goals and quantify 1 analysis them

3 11. Examining alternative solutions and evaluating

proposed solutions a) Technical feasibility 1 b) Operational feasibility c) Economic feasibility

12. Cost benefit analysis, Documenting feasibility 1 report

5. Tools for systems analysts

13. Developing Data Flow Diagrams (DFD) a) What are DFDs? b) Symbols used in DFD c) Rules of data flow d) Good style in drawing DFD

1.5 3

14. Describing systems with DFD & Leveling 1 DFD

15. Logical & Physical DFDs 0.5



6. Structured 16. Structured English specification 1 systems analysis 17. Decision table based specification 1 and design

4.5

18. Detecting 19. Incompleteness 20. Ambiguity 21. Contradictions 1 22. Redundancy 23. in decision table specification

24. Eliminating redundancy in specifications 1 25. Decision trees for specification 0.5

7. Data oriented 26. Entity-relationship (E-R) modeling 1 systems design 27. of data elements of an application

28. Organization of data as relations 0.5 529. Normalization of relations 1

30. Creation of logical relational database 1 31. Objectives of database management system 1

(DBMS) 32. Overview of DBMS 0.5

8. Data input 33. Data input methods, coding techniques, 1 methods requirements of coding schemes

334. Error detection of codes, validating input data 1 35. Input data controls interactive data input 1

9. Designing 36. Designing outputs, output devices, designing 1 outputs output reports

237. Screen design, graphical user interfaces, Interactive I/O on terminals.

1

10. Object 38. Object oriented systems modeling 0.5

4

oriented systems modeling

39. What are objects? Why objects? 0.5 40. Objects and their properties, classes,

inheritance, polymorphism 1

41. How to identify objects in an application, how 1 to model systems using objects

42. Some cases of object oriented system 1 modeling

11. Control-audit and

43. Control, audit and security of information system

0.5

security of 44. Why controls are needed, objectives of control, 0.5 information techniques used in control

4systems 45. Auditing information systems, auditing around, through and with the computer

1

46. Testing information systems, types of tests, 1 how to generate tests



47. Security of information systems, disaster 1 recovery, business process continuity

12. Systems 48. Systems analysis and design in the era of 0.5 analysis and electronic commerce design in the era 49. B2B, B2C and C2C e-commerce, advantages 0.5 of electronic and disadvantages of e-commerce. 4 commerce 50. E-commerce system architecture 1

51. Physical networks, logical network, world 2 wide web, web-services html, XML

13. Electronic data interchange

52. Electronic data interchange, EDI standards 1 253. Virtual private networks XML and EDI. 1

14. Security of e- 54. Security of e-commerce transactions, firewalls, commerce encryption methods, symmetric and 1.5 transactions, asymmetric encryption, 3 firewalls 55. Digital signature, certifying authorities for

signatures, legal status of e-commerce transactions

1.5

15. Payment 56. Payment systems in e-commerce, cheque systems in e- payment, credit card payments, e-cash 2 2 commerce payments. 16. Complete 57. Complete system analysis and design case system analysis studies, a system for journal acquisition in 5 5 and design case libraries, walk through the entire life cycle studies


System Analysis and Design/ Data and Information Learning Objectives

Learning Objectives

Distinction between Data and Information

Description of types of Information: Tactical, Operational, Strategic and

Statutory.

Division of Management into different hierarchical levels.

Type of Information needed at different levels of management.

Division of organizations into several functional areas and their information

Requirements

Attributes of Information.

V. Rajaraman/IISc. Bangalore //V1/June 04/1

System Analysis and Design / Data and Information Motivation

Motivation

Large number of jobs today for computer science and engineering graduates is in

creating information systems for managing organizations we thus need methods to

design complex systems.

Students should know what information is and how it is different from data.

Should know types of information needed to manage organizations.

Should know nature of organizations and their structure to design appropriate

information system.

Should know management structure and needs of each level of management.

Should know functional areas of management information needs for each area.

V. Rajaraman/IISc. Bangalore //V1/July 04/1

V.Rajaraman SAD/M1/LU1/V1/2004 1

Data and Information

Data : Raw Material

Data collection costs money

Collect only necessary and sufficient data

Data is generally used by machines

Data is useless unless it is processed to

create Information


Data and Information

Information : Processed data

Data processed by machines giving information

Information is used to run an organization efficiently

Information used by managers to initiate actions


Example of Informationneeded by a Shopkeeper

Daily sales account

List of low stock items to be re-ordered

List of overstock items

Long overdue payments

Profit and loss account

Used to streamline day to day operations called

Operational information


Example of Informationneeded by a Shopkeeper (Contd)

Slow or fast moving items

Reliable supplier of items

Sales trends

Used to improve profitability of shop called

Tactical information


Example of Informationneeded by a Shopkeeper (Contd)

Whether to stock different varieties of items

Whether to diversify

Whether to start a new branch in a different locality

Whether to start an e-shop

Information to expand business and explore new opportunities

Known as Strategic Information


Example of Information needed by a Shopkeeper (Contd)

Income tax account

Sales tax account

Used to provide information to the government

Known as Statutory Information


Types of Information

Strategic : Needed for long range planning and directions.

This is less structured.

Tactical : Needed to take short range decisions to improve

profitability and performance.


Types of Information

Operational : Needed for day to day operations

of the organization.

Eg: Daily Sales, Billing.

Statutory : Needed by law to sent to government

authorities.

Eg: Sales tax return.


Management Hierarchy and Information Needs

Volume ofInformation

Type ofInformation

TopManagers

MiddleManagers

Line managers

Strategic-Long range planning

TacticalShort range improvement

OperationalDay to day policies

Lowcondensed

Unstructured

Mediummoderatelyprocessed

Moderatelystructured

LargeDetailed Reports

Highlystructured

SAD/M1/LU2/V1/2004 1V.Rajaraman

Need forInformation Systems

Increasing size of organizations thus data volume increases

Timely processing for fast action

Better competitiveness with better information

Increasing of complexity of organizations requireinnovative processing

Distributed organizations

Same data can be processed in different ways


Management Structure

Chief Executive (Strategical)

Marketingmanager

Human Resourcemanager

Financemanager

Materialsmanager

Productionmanager

(Tactical)

Line managers(Operational)


Management Structure(Contd)

Top Management

Chief Executive known as CEO

Executive Directors for each functional areas such as

Production, Finance, HRD etc.

Take strategic decisions



Middle Management

General managers, divisional managers, Vice presidents etc

Each functional area may have 2 to 3 middle level

managers reporting to top management

Take Tactical decisions



Line Managers

Group managers, Assistant Group managers, Assistant managers

Each functional area may have several line managers reporting to

middle level managers.

Take Operational decisions

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Functional Areas

Production

Marketing

Materials Purchase, Stores

Finance Accounts

Human Resource Development (hrd)

Research And Development (R&D)



Functional Areas

All organizations need not have identical functional areas

However some are common such as

- Marketing

- Finance

- Human Resource Development (hrd)


Information for Management

Production Management

Strategic Information

Yearly and monthly production quotas and alternate

schedules

Policies on machine replacement, augmentation,

and modernization.

Identifying best product mix.


Information for ManagementProduction Management

Tactical Information

Identifying and controlling areas of high cost.

Identifying critical bottlenecks in production.

Identifying alternate production schedules based on tools,

machines etc.

Performance measures of machines to decide replacement.


Information for ManagementProduction Management

Operational Information

Monitoring up to date production information by examining

assemblies, detecting likely shortages and giving early warning.

Scheduling better production dynamically.

Preventive maintenance schedules.

Monitoring tool, machine and personnel availability



Marketing Management


Search for new markets and marketing strategies.

Analysis of competitors strategy.

Technology and demographic forecasts and

product changes.


Information for ManagementMarketing Management

Advertising techniques and analysis of their impact.

Customer preference surveys.

Correlation of prices and sales.

Sales force deployment and targets.

Exploring alternate marketing channels.

Timing of special sales campaigns.



Information for ManagementMarketing Management


Sales analysis by regions, customer class, sales person. Sales target versus achievement. Market share and trends. Seasonal variations. Effect of model changes. Performance of sales outlets Costs of campaigns and benefit.



Material Management


Developing vendors for critical items.

Determining optimal levels of inventory

Determining proportion of material needed

Reducing varieties of inventory.


Information for ManagementMaterial Management


Developing vendor performance measures.

Determining optimal reorder levels.

Determining issues of items to shops versus standard needs.

Controlling high value of inventory.

Determining impact on material cost and procurement with

design changes and new product introduction.


Information for ManagementMaterial Management


List of excess & deficient items received.

List of items rejected.

Critical items received.

Stores in transit and in inspection.

Value of inventory in hand.

Goods received, rejected and issued.



Finance Management


Methods of financing.

Pricing policies.

Tax planning.



Finance Management


Variations between budget and expenses. Large outstanding payments/Receipts. Credit and payment status. Cost increases and pricing. Impact of taxation on pricing



Finance Management


Periodic financial report. Budget status to all functional managers. Tax returns. Share transfers. Profit and loss account. Payments and receipts. Payroll, provident fund accounts.



Human Resource Management


Long range human resource requirements

at different levels.

Policies on human resource development and training

Policies on personnel welfare and facilities


Information for ManagementHuman Resource Management


Performance appraisal. Demographic make-up of personnel and its

impact on retirement. Production incentives. Morale of personnel. Absentee reduction. Leave and overtime policies. Personnel deployment policies.


Information for ManagementHuman Resource Management


Routine assessment.

Skills inventory.

Loan/advances and recoveries.

Leave record.



Research Design & development Management


Which products are to be developed?

What types of improvements are required?

What long range research is more promising?

What technical collaboration would be appropriate?





Setting intermediate goals. Checking availability of equipment & appropriate selection Determining proportions of resources to be allocated to different projects.

Deployment of personnel to projects. Information on similar and related researchprojects undertaken by other companies





Progress against goals.

Budgeted expenses versus actual expenses.

Status of outstanding orders for equipment and

components.


Qualities of Information

Quality How to ensure quality

Accurate Ensure correct input and processing rules.

Complete Include all data.

Timely Give at right time




Trustworthy Do not hide unpleasantinformation.

Relevant Understand user needs.

Brief Summarize relevant

information.




Up-to-date Include all data up topresent time.

Significance Use attractive format & graphical charts.


Varieties ofInformation Systems

Business Data processing

Operational information

Management information system

Tactical information

Decision support system(DSS)

Strategic information


Business DataProcessing System

Enter data to be processed

Edit, check input data

Control check to see if the data is correct and

reasonable

Store clean data as an organized data base in a storage


Business Data Processing

There are 2 methods of business data processing1. On-line transaction processing (OLTP)2. Batch processingOLTP is used for query processing and rapid actions to requestsExample: Finding balance in ones bank account

Booking railway ticketsBatch processing used for periodic data processing of massive dataExample: Processing university exam results at the end of

each semester Payroll computation each month


OnlineTransaction Processing

Database (or master file) available online on disk

Request in specified format accepted from requestor

Check request for validity

Retrieve record from database

Take appropriate action


Batch Processing

Collect a batch of requests

Key in

Validate

Create request file

Called transaction file

Update master file using transaction file

Create result file

Print responses for requests


OLTP Vs Batch

Response time - OLTP Fast Throughput

(No of transaction/unit time) - Batch High Enquiry systems - Online Periodic Processing - Batch

Once a day - Stores Issues Once a month - Payroll


ManagementInformation System

Analyze outputs of routine data processing using

statistical or operations research tools

Eg: -Observe periodic demands by statistical analysis &

use for tactical decisions

- Use operations research tools to decide product mix

using demand and cost data to maximize profit


Decision Support System

Unstructured and difficult to obtain precise information

Use of analytical and simulation models

Aids to conceptualise through graphs ,animation etc

Use of archival data to infer trends and rules

Some artificial intelligence tools may be used



Data mining a useful tool

What is data mining?

Data collected during routine data processing archived

over a long period-massive amount (Tera Bytes)

Some hypothetical rules guessed by experienced managers

and correlated with archival data-called data mining



Example of data mining From archival data a rule guessed by managers

that in some months there are long waiting lists for sleeperberths is verified-Data mining gives precise quantitative data

Action

Increase number of sleeper coachesor

Introduce special trains

Unexpected results of analysis of archival data morevaluable for DSS

System Analysis and Design/Systems Analysis and Design Life Cycle Learning Objectives


Learning Objectives

Nine Steps in designing Information Systems Tasks performed in each step. Nature of tasks performed by Systems Analysts. The attributes of Systems Analysts. The tools used by Systems Analysts

System Analysis and Design/System Analysis and Design Life Cycle Motivation

V. Rajaraman //V1/July 04/1

Motivation Designing Information system for an organization is very complex job.

Students should know how to logically divide a complex job into smaller

manageable steps. Each step must have a logical beginning and end and must be self contained.

Division of large jobs into logical steps will

Enable one to assess progress at the end of each step Steps may be assigned to persons with specialized competence Allocation of human and financial resources appropriate for each step can

be planned


Steps involved in Analysis and Design

Life Cycle Of Systems Analysis And Design

1. Requirements Determinations2. Requirements Specifications3. Feasibility Analysis4. Final Specifications5. Hardware Study6. System Design7. System Implementation8. System Evaluation9. System Modification



Step 1 : Requirements Determination

Arrived at by a consensus among managers

Priorities among applications determined

Pick high priority applications.



Step 2 : Requirements Specification

Known as System Requirements Specification (SRS) Understand the existing System Applications where a system is required are listed Arrive at the specifications of the users Requirements

after discussions with the user

A system may encompass several applications

V.Rajaraman SAD/M2/LU2/V1/2004 1V.Rajaraman SAD/M2/LU2/V1/2004 1

Step 3 : Feasibility Analysis


Formulate Goals of the system and quantify goals Find alternative methods of meeting the goals For each alternative assess resources needed

- Human Resources

- Time and Money

- Equipment needed

Assess cost of each alternativeFind the best alternative method subject to resource

constraints



Step 4 : Final Specifications

Specifications would state what the system wouldachieve.

Specification drawn up are improved forimplementation.

SRS written- given to user and agreementreached



Step 5 : Hardware Study

Determine Hardware and Software requiredto execute the application.

Determine Response time,Volume of data to be processed, Frequency of reports etc & then

pick the hardware.



Step 6 : System Design

Logical Design of the System Objects Identified Database Designed Program Specification drawn up Implementation Plan Drawn up Test Plan



Step 7 : System Implementation

Write Programs Create Database Document System Train Users Trial run of the system Test and Accept



Step 8 : System evaluation

Find out from Users whether the Systemmeets specified requirements.

List areas of dissatisfaction and find reasons Suggest if there has to be any improvements to

the system



Step 9 : System Modification

Fix errors Add/Delete features as required by users Tune the Syste Continuously monitor system and assess

performance


RequirementsDetermination

RequirementsSpecification

FeasibilityAnalysis

SystemImplementation

SystemDesign

SystemSpecification

Analysis

HardwareStudy

SystemEvaluation

SystemMaintenance Improved System

RevisedRequirements

Budget & schedule

PhysicalRequirements

ConfigurationData

LogicalDesign

UserRequirements

FeasibilityStudyFunctional

Specifications

Decision toDesign Information System

Revised PrioritizedRequirements Specifications

Test Plan

System Life Cycle Diagram

System


Role Of Systems Analyst Defining Requirements

- Involves Interviewing Users

Prioritizing Requirements- Obtain Users Consensus

Fact Gathering- Data, Facts, Opinions of Managers

- Lower level Users should be consulted


Role Of Systems Analyst Analysis and evaluation

- Arrive at appropriate system

Solving problems- Hazy requirements converted into specific requirements

- Suggest many alternative solutions

- Quantify cost and benefits


Role Of Systems Analyst

Drawing up specifications- Functional Specifications

- Understood by users and programmers

- Accepted by users

- Precise and detailed

- Account for possible changes



System Design

Logical design of system- Objects identification

- Normalizing database

- Test plan

Design must be modular to accommodate change



Evaluating Systems - Evaluation after use for sometime

- Plan periodicity for evaluation

- Modify as needed


Attributes Of A Systems Analyst

Knowledge Of Organisation- Knowing users jargon & practices

- Know Management functions.

Knowledge Of Computers And Software - Knowledge of system design tools

- Keep abreast of modern developments



Good Interpersonnal Relations- Need to work as team member

- Lead smaller teams

- Interface with programmers & Users

- Motivator.

Ability To Communicate- Oral Presentation

- Report Writing

- Answer queries



Analytical Mind- Problem solving attitude

- Ability to assess trade offs

- Sound commonsense

- Curiosity to learn about new organizations

Breadth Of Knowledge- Broad Liberal Knowledge

- Variety of jobs to be tackled in diverse organizations


Tools Used By Systems Analyst

Data Flow Diagram Decision Tables Modeling Language such as UML Normalization of Databases Testing tools ISO/CMM procedure manuals

System Analysis and Design/ Information gathering Learning Objectives


Learning Objectives

Strategy to gather information for computerization. Various sources of information. Methods of searching for information. Interviewing techniques to gather information from line managers to top

management.

Methods of consensus for formulating requirements. Use of document flow diagrams to depict flow of documents in an organization Specification of Operational, tactical and strategic information which will be

provided by the system

Use of dataflow diagrams to specify flow of records and how they will be processed to create reports

System Analysis and Design/Information Gathering Motivation

V. Rajaraman //V1/July 04/1

Motivation

The Information system designed for an organization must meet the requirements of the end users of the organization.

To obtain what an end user expects from the Information System the designer must gain complete knowledge of the organizations working.

It is important for the student to know the information gathering techniques so that no information is overlooked and the nature and functions of an organization

are clearly understood

The main purpose of gathering information is to determine the information requirements of an organization.

Information requirements are often not stated precisely by management. Analysts responsibility to prepare a precise Systems Requirement Specifications

understood (SRS) by users.

SRS document is a vital document before starting a project.

V. Rajaraman SAD/M3/LU1/V1/2004 1

InformationGathering Strategies

Identify Information sources

Evolve a method of obtaining information from

the identified sources.

Use Information flow model of organization.


Information Sources

Users of System

Forms and Documents used in the organization

Procedure manuals, rule books etc.

Reports used by the organization

Existing computer programs(If Any).


Information Sources

Interviews are very important

Use organization chart

Understand the importance of the people who

operate the system-Clerks,Line managers.

Gather information from Middle level persons who have lot of

experience

Gather both qualitative and quantitative

information & Observe how the organization works.


InformationGathering Methods

Searching for information

Individual Interviews

Group discussions

Several Interviews needed.


Planning an Interview

Make a list of people to be interviewed and in what order

Plan and note down a list of questions to be asked

Plan several interviews with same person-mainly to

clarify doubts

Interview groups as appropriate


Interviewing Technique

Make appointment

Allot time

Read background material

State purpose of interview

Be punctual and pay attention to what user says

Do not use computer jargon


Interviewing Technique

Obtain both quantitative and qualitative Information

Discriminate between essential and desirable requirements

State what you understand and get it confirmed

Do not prolong interview

Summarize information gathered and get it checked by the

interviewee


Use of Questionnaires

Questionnaires useful for statistical data collection

Useful when large number of persons have to respond

Make questionnaires short

Design questionnaires by enumerating objectives and

data needed to meet the objectives

Several follow-ups/personal interviews may be required to

get questionnaires back from respondents


Existing system(If any)

Systems in similar organization

Observe workflow in workplace

Case repository in own organization

InformationGathering other Methods


SystemRequirements Specification

System requirements specification specifies what

Information requirements will be provided.

It does not specify how the system will be designed

SRS is obtained after excessive discussions with the user.

Developing SRS is most important and difficult task of

a Systems analyst


System RequirementsSpecification

Analyst examines the current system if any.

Analyst finds out the shortcomings of the system as

seen by the user.

Analysts aim is to develop SRS which is understandable by the

user and which can be used for detailed design of the system.

How SRS is Developed



Complete and Unambiguous.

Specifies operational,tactical, and strategic information

requirements

Eliminates possible later disputes between users and Analyst

Uses Graphical aids understood by users who are not

computer literate and will also be useful in design.

Jargon Free.

Ideal characteristics of SRS


From WordStatement to Srs

Narratives of requirements by users too long and imprecise

Needs conversion to precise specifications

Step1: Analyse statement

Step2: Identify physical entities such as vendors,

receiving office, Inspection office etc.

Step3: Identify documents which are received/sent by

each office

Step4: Draw a physical document


Developing aDocument Flow Diagram

Example Word Statement:

Our company receives many items from several vendors each

accompanied by a delivery note. A receiving office receives the

item and checks the delivery note with corresponding order.

Any discrepancy is reported to purchase office. The items received

along with items received note (with details of items) is sent to the

inspection office.


Entities Identified - Vendors, Receiving office, Inspection office

Documents Identified - Delivery note, discrepancy note, Items

Received note.

Using these a document flow diagram is drawn

Developing aDocument Flow Diagram



Physical document flow diagram.

Logical Data flow Diagram (abbreviated as DFD)

Document flow diagram depicts various entities or offices &

documents generated/transmitted by these entities

Graphical Specification Tools


Entities represented by Rectangles, Document flow by lines,

direction is shown by arrows.

Document flow lines are labeled by name of the document

Dashed lines used to depict flow of physical items.

Document flow diagram depicts various entities and

documents generated and/or transmitted by these entities

SystemRequirements Specification


Document Flow Diagram

Vendor ReceivingOffice

Inspection office

Purchase Office

Delivery note ItemsReceived note

Discrepancynote

Delivered Items

Entities in the Document flow diagram given above are Vendor,

receiving office, Inspection office and purchase office

Documents are:Delivery note,items received note and discrepancy note

Physical flows are delivered items


Document Flow Diagram (Contd)

Vendor ReceivingOffice

Inspection office

Purchase Office

Delivery note ItemsReceived note

Delivered Items

Discrepancynote

Delivered Items


The diagram is interpreted as follows:1) Vendors deliver items to receiving office accompanied

by a delivery note2) Receiving Office sends items to inspection office along

with an items received note3) Receiving office sends discrepancy note to Purchase

officeEntities: Vendor,Receiving office,Inspection office and purchase officeDocuments : Delivery note,Items received note and discrepancy note

Document Flow Diagram (Contd)


Data Flow Diagram (Dfd)

DFD also has entities and data flows

Besides this DFD specifies processing performed by some of the

entities

Data flow diagrams specify which entities generate documents

Details of documents and their flow

Processing performed by some entities

Data stores which are referred while processing data and in

which processed data may be written or stored


Data Flow Diagram (Dfd)

VendorReceiving

Process

InspectionOffice

PurchaseOffice

Orders

Delivery note

ItemsReceivednote

Discrepancy note


Entities are, originators of data and consumers of data

Vendor, Inspection office and purchase office are entities in

the above diagram

Data flows are delivery note, items received note

and discrepancy note

A circle is used to depict a process

A pair of parallel lines depict a store

Data FlowDiagram (Dfd) Contd.


Data Flow Diagram (Contd)

VendorReceivingProcess

InspectionOffice

PurchaseOffice

Orders

Delivery note

ItemsReceivednote

Discrepancy note


1) Data in a store may be read by a process

2) Processed data may also be written in a store

3) Circles depicting process are detailed separately

using Structured English Algorithms Or decision tables

4) Data flows are expanded to detail the data elements

5) Contents of the data stores are also detailed

Data Flow Diagram (Contd)


Data Elementsin Data Flow & Store

Delivery note:

Order no,Vendor code,Vendor name and address,Item name,

Item code, Delivery date,Quantity supplied,units.

Items Received note:

Order no, Item name, Item code, Delivery date, quantity

supplied, units.


Discrepancy note:Order no,Vendor code, Vendor name and address, Item name,Item code,Order date, Delivery date, quantity supplied, units,excess/deficiency, No of days late/early.Receiving office order file:Order no, Order date, Item name, Item code,Vendor code, VendorName and address, Quantity ordered, delivery period.

Data Elementsin Data Flow & Store


Processing Rule

English statement

1. Compare order no in delivery note with that in order file. If no

match return item to vendor.

2. If order no matches then compare item codes, if no match return

item to the vendor.

3. If order number matches compare qty delivered with quantity

ordered. If excess or deficient send discrepancy note to purchase

office.


4. If order number matches compare date of delivery with

expected date. If late or early send discrepancy note to

purchase office.

In case3 and case4 send items received note to inspection

office.

The above statements are shown to the user for his approval.

Processing Rule


Operational, Tacticaland Strategic Information

For this simple examples are:Operational: Automatic checking of delivery against order and create

discrepancy note.Note discrepancy (if any) of each order.Tactical: Evolve vendor performance index based on discrepancy in

supplies and quality inspection.Strategic: Use performance index to decide proportion of order for an

item to be placed with each vendor.Develop new vendors if all existing vendors performance are poor.


Steps In System Analysisand Design

Study currentsystem

DesignLogicalsystem

New System model

User statedrequirements

Physical document flow diagram

Logical data flow diagram

Feasibility document

New logicalDFD

Data DictionaryProcessing

rules

DescriptiveStatement of Information


Modularizing Requirements Specifications

SRS Document now consists of:

Document flow diagrams (as many as needed).

Data Flow Diagrams.

Data elements of each data flow and Data Store

SRS Document


Modularizing Requirements Specifications

Processing rules carried out in each circle of DFD.

A descriptive statement of operational,tactical,strategic

information will be provided

A data dictionary which consolidates all data elements

in the document and data store.

SRS Document ( Continued)

System Analysis and Design/ Feasibility analysis Learning Objectives

Learning Objectives

How to formulate the goals to be met by the information system to be designed How to quantify the goals How to obtain alternative solutions to satisfy the goals How to assess the feasibility of implementing alternative solutions. How to compute cost vs benefits of each alternative feasible solution How to prepare a system proposal for the potential users of the system


System Analysis and Design/ Feasibility analysis Motivation

Motivation

Before a management decides to implement a computer based system they should know the goals which will be met by the system

These goals should primarily be quantitative goals so that when the system is implemented it is possible to compare quantitatively the achievements with the

original goals set.

Analysts should also be able to estimate what hardware and human resources will be needed to implement a system to meet the goals

Analyst must examine alternative methods to implement the system and their resource needs.

A cost-benefit analysis should be carried out for each alternative and given to the management

This analysis will be essential for a management to decide which solution they would like to implement

Feasibility of meeting goals with available technology and human resource and cost/benefit are important parameters for informed management decision making.

V. Rajaraman/IISc, Bangalore //V1/July 04/1


Feasibility Analysis

The following are the results of the Information gathering phase:

Deficiency of the current system are found Consensus is arrived at on requirements SRS Document is prepared


Steps In Feasibility Analysis

Evaluate feasibility of alternative solutions taking into account constraints on resources.

Rank order alternatives and discuss with user.

Prepare a system proposal for management approval


Feasibility Analysis (Contd.)

Send bill within 5 days of month end

Find out whether it is possible to meet these goals.

Determine the cost of meeting each goal

Find cost benefit if quantified


Guidelines For Searching Goals

Identify the deficiency by pinpointing-Missing Functions

-Unsatisfactory performance

-Excessive cost of operations

Set Goals to remove deficiency and provide competitive advantage


Characterstics Of a Goal

Must be quantified Realizable with the constraints of the organization and the system

Broken down into Sub-Goals Agreeable to all concerned In general goals must not only remove deficiency but also give a system which is superior to those of the competitors of the organization


Case Study-hostelInformation System

(Detailed description of case is given in module3)

DEFICIENCIES OF CURRENT SYSTEM IDENTIFIED

MISSING FUNCTIONS

1.1 Stores requirement not forecast

1.2 Purchases not consolidated

1.3 Daily rate calculation not frequently updated

1.4 Menu not planned for balanced nutrition and low cost



DEFICIENCIES (BAD PERFORMANCE) UNSATISFACTORY PERFORMANCE

2.1 Billing not accurate and prompt

2.2 Student bills not itemized

2.3 Stores issue to cooks arbitrary

2.4 Payments to vendors not prompt

2.5 Large variations in mess bills every month



DEFICIENCIES (HIGH OPERATIONAL COST)

3.1Unpaid and long outstanding bills from students

3.2 Extras and rebates not reflected in stores issues

3.3 Frequent small purchases at high cost

3.4 High transport cost due to not consolidating stores requirements



FORMULATIOIN OF GOALS

MAIN GOALS

Ml . Send bill to students within 5 days of the end of month

M2. Control inventory of items in stores & issues to cooks to bring down mess bill by 10%

M3. Balance menu to meet nutritional requirements

M4. Cost of new menu not to exceed current cost



Formulation Of Sub-goals

S1.1 Itemize bills showing extras and rebates with dates

S1.2 Ensure less than 5% variations of bills from month to month

SI.3 Bills not paid within 10 days of issue brought to the attention of chief warden

S1.4 Update daily rates every day

Main goals M1 and sub-goals S1.1,S1.2,S1.3 remove deficiencies 1.3,2.1,1.2.2,2.5,3.1



FORMULATION OF SUB-GOALS

S2.1 Ensure payment to vendors within five days of

supply of items

S2.2 Maximum 4 trips per month for purchases.

Cartage less than 1% of item cost


Case Study-hostel Information System (Contd.)

S2.3 Reduce inventory level. Level not more than 10% of requirements in a month

52.4 Issue to cooks every day not to exceed 5% of calculated values

Main goals M1& sub-goals above remove deficiencies1.1,1.2,2.3,2.4,3.2,3.3,3.4


ExaminingAlternative Solutions

HOSTEL INFORMATION SYSTEM

ALTERNATIVE SOLUTIONS

A: Improve manual system

B: Use PC based periodic update system

C: An on-line system with server and several clients


Solution A:Manual System (Contd.)

Calculate standard quantities needed and use for vendor order

Track student payments to find overdue payments

Solution does not ensure reduction in bill variations and prompt payment to vendors

Solution not scalable to large student population


Solution B

Use a single PC to

Prepare students bills-itemize bills

Prepare number of members who will eat for next two days

Alert warden when bill not paid within 10 days of issue

Vendor order generation

Inventory control of store

Menu planning


Solution B (Contd.)

PC configuration needed based on data base sizes PC with 20 MB disk, 1.2 MB floppy sufficient However minimum configuration available today(2004) is PC with 128 MB main memory, 40 GB disk 1.2MB floppy & CD R/W costs Rs. 25,000.Systems software(Windows XP+MSOffice+anti-virus) will cost around Rs.25,000.

Total cost=Rs 50,000 Need PC+ printer+uninterrupted power supply cost Rs. 70,000


Solution C

Use a server which is accessed by 3 clients one each in the mess, the stores and the accounts sections; perform on-line transaction processing.

Advantage: Up to the minute status can be found

Number of transactions small and does not justify 4 computers

Solution unnecessarily expensive and rejected 0


Evaluating Alternative Solutions

Determine Technical feasibility of each solution,in other words is technology mature to implement a solution

Determine Operational feasibility of each solution.In other words,for a given organizational structure will the solution fit in.Will it provide right information at the right time to users


EvaluatingAlternative Solutions (Contd.)

Determine Economic feasibility of each solution.In other words, are finances available to implement system?Will it be cost effective?Will the money spent be recovered by savings or by better services to users


Technical AndOperational Feasibility

Solution B is selected for further consideration

It is technically feasible as PC of necessary configuration is easily available.

It is also operationally feasible as clerks in hostel office can be easily trained to use a PC. The necessary problems will be written by system analyst/ programmer hired for this purpose.


Cost-benefit Analysis

Needed to find economic feasibility of proposed solution Objective to find whether returns by implementing a system

justify the cost Found by listing all costs direct and indirect


Cost-benefit Analysis (Contd.)

Direct cost- Cost of computer, software, space, human resource,material, travel, training etc.

Indirect cost- Time spent by persons and data gathering Benefit- Tangible- measurable

Intangible - better management- better user satisfaction


Benefits

Direct - Savings due to reduced inventory, early collection of outstanding payments, reduced wastage,faster production, increased production

Indirect Increased work done with same human resource

Intangible - better service to customers

- superior product quality

- accurate,reliable,timely and up-to-date

strategic,tactical and operational information to

management


Cost Benefits Analysis

CASE STUDY OF HOSTEL INFORMATION SYSTEM

COST : PC,UPS,Printer+Systems analyst+programmer

Capital 70,000 +60,000 =1,30,000

Cost(Recurring) : Stationery, maintenance,floppy etc.

Rs. 2000 per month


Cost Benefits Analysis (Contd.)

Benefits : - Inventory reduction 5% of mess bill of 400 students

Daily rate=Rs 45Savings= 45*0.05*30*400=Rs 27,000- Transport cost saving=Rs 800 per month- Savings due to early payment=material cost*1.2%=37.5*400*30*0.012=Rs 5400 - Savings due to early collection =40*1350*0.01=Rs 540


Cost Benefits Analysis

Direct saving=33740

Indirect benefit : student satisfaction due to itemized bill,

predictable daily rate,better menu

Net Direct Saving per month= 33740-2000

=R31740

Total capital cost=l,30,000


Pay Back Period

SIMPLE: Cost 1,30,000

Saving 31,740 per month

Cost recovered in 130000/31740 = 4.1 months

Using interest on capital:

Monthly interest=0.015* 1,30,000

=Rs 1950 per month

Saving per month=31740-1950=29790

Cost recovered in 130000/29790 = 4.4 months


Present Value Method

Accounts for the fact that a benefit accruing n months later will be lower today as the money if available today would have earned interest

If r = Interest rate in % per month.

n = number of months

x = benefit

Present value of benefit accruing n months later is:

Present value = x/(1+r)n

System Analysis and Design/ Tools for systems analysts Learning Objectives

Learning Objectives

What are Data Flow Diagrams (DFDs)? Why they are useful? How are they developed? How to level DFDs? Good style conventions in developing DFDs Difference between Logical and Physical DFDs Tools available to draw DFDs


System Analysis and Design/ Tools for systems analysts Motivation

Motivation

WHY DFD ?

Provides an overview of

-What data a system processes

-What transformations are performed

-What data are stored

-What results are produced and where they flow

Graphical nature makes it a good communication tool between

-User and analyst

-Analyst and System designer

Structure of DFD allows starting from a broad overview and expand it to a hierarchy of

detailed diagrams



Data Flow Diagrams

WHAT ARE DATA FLOW DIAGRAMS?

DFDs models the system by depicting

External entities from which the data flows and where

results terminate

Processes which transform data flows

Data stores from which the data are read or into

which data are written by the processes.


Symbols Used In Dfd

1.STORES

Stores demandnote

Delivery slip

Issue Advice

PROCESS

A circle represents a process Straight lines with incoming arrows are input data flows Straight lines with outgoing arrows are output data flows Processes are given serial numbers for easy reference Labels are assigned to Data flow.These aid documentation


Symbols Used In Dfd

EXTERNAL ENTITIES

VENDOR CustomerInvoice

Order

Bill

A Rectangle represents an external entity They either supply data or receive data They do not process data


Symbols Used In Dfd

DATA STORES

Inventory Writing Reading

A Data Store is a repository of data

Data can be written into the data storeThis is depicted by an incoming arrow

Data can be read from a data storeThis is depicted by an outgoing arrow

External entity cannot read or write to the data store

Two data stores cannot be connected by a data flow


Rules Of Data Flow

Data can flow from-external entity to process-process to external entity-process to store and back-process to process

Data cannot flow from-external entity to external entity-external entity to store-store to external entity-store to store


Data Flow Diagrams

An alternate notation is often used

3StoreIssue

Label

Name

A Process

NameLabel

DS1 InventoryA Data store


Good Style In Drawing DFD

Use meaningful names for data flows, processes and data stores.

Use top down development starting from context diagram and successively leveling DFD

Only previously stored data can be read

A process can only transfer input to output. It cannot create new data

Data stores cannot create new data


SAD/M5/LU2/V1/2004V.Rajaraman 1

Describing A System With A DFD

An entire system is represented by one DFD which gives thesystems overview

It is called a context diagram

It gives little detail & is also known as the top level DFD Context diagram of mess management is shown in the nexttransparency



Context Diagram OfMess Management System

MessManagement

System

Students

Mess manager Chief warden

Mess secretary

VendorsRequisitionsPayments

Daily rate

Menu

Overdue Payments

Item neededEach day

PerishableItems

BillsPayments

Extras Note

Supplies

Overdue Bills

Observe this diagram gives very little detail



Levelling DFD

A context diagram gives an overview

It should be split into major processes which give greater detail.

Each major process is further split to give more detail.

This process of giving more detail at a finer level is called levelling of DFD



Why Level DFD?

If a DFD is too detailed it will have too many data flows and will be large and difficult to understand

Start from a broad overview. Expand to details - Idea similar to using procedures and linking these with a main program

Each DFD must deal with one aspect of a big system



Expanded Dfd For Hostel Mess Management

1Billing system

StudentsMess

Secretary Chief Warden

Mess manager

Payments Update dailyrate Unpaid bills

Itemized billsat end of month

Extras/RebatesExpenses

No of meals(today +3)

Items used each day

Student billingInformation + bills

Going to next process (Continued in next slide)



Expanded DFD ForHostel Mess Management

3Perishableordering

2Stores issue

and Controlsystem

MessSecretary

MessManagerVendors

Orders(perishable) Vendor data(perishable)

Vegetables and perishablerequisition

Vendor dataStores

inventoryOrder data

Items usedtoday

Items to be issued(today +2)Vendor supplies

Order non-perishable

Menu(today +2)

Perishable order

Continued Low stock (today+2)



ExpandedDFD-billing System

Items rate data

1.4Find no

Of meals to cook

1.1CalculateDaily rate

1.2CalculateStudents

bills1.3

Reconcilepayments

Chiefwarden

MessManager

MessSecretary

Payments

Unpaid bills

Students dataDaily rate average(upto date)

Expenses data

Students data

No of meals(today + 2)

Students data

Itemizedbills

Bills

Extras/Rebates

Observe numbering of processes



Levelling Rules

If process p is expanded, the process at the next level are labeled as p.1,p.2 etc.

All data flow entering or leaving p must also enter or leave its expanded version.

Expanded DFD may have data stores

No external entity can appear in expanded DFD

Keep the number of processes at each level less than 7.



IllegalConstructs In DFD

No loops are allowed in DFD

A process cannot be a pure decision

CompareActual rate > Standard rate

Actual rate



IllegalConstructs In DFD

Get studentsextra/rebates

record

Calculate Bill

Extra/rebate store

Record

Ask for next record

Not correct as loop is formed



Levelling Examples

2Stores issue

and control system

Mess secretary

Vendor

Mess manager

Menu for(Today +2)

Vendor supplies

Vendor

Low message stock

Items issued

Items to be used on (today +2)

Low stock item(today +2) No of meals to

be cooked (today +2)

Stores inventory

Order for items

Order

Stores issue control system process



Levelling Examples

2.1Inventory update

And low stock warning

2.2Create orderfor vendor

2.4Check Itemavailability

2.3Calculate Items

needed

Mess manager

Mess secretary

Vendor

Items used today

Low stockitem

Stores inventory Order Vendor data

Items neededFrom 2.3

Vendor supplies

Order to vendor

Menu(today +2)

Items needed Low stock items(today+2)

Stores inventory

No of meals to (today +2)



Levelling ExamplesTop

Level process Ext BExt A

1 2 4

3

Ext BExt A

F1

1.1 1.2 1.4

1.3

2.1 2.2 2.3

F1

Ext A

Process 1 Process 2

F4

Ext B 4.3 4.1 4.23.1 3.2 3.4

3.3F4


Logical And Physical DFD

DFDS considered so far are called logical DFDs

A physical DFD is similar to a document flow diagram.

It specifies who does the operations specified by the logical

DFD Physical DFD may depict physical movements of the goods Physical DFDs can be drawn during fact gathering phase of a life cycle


Physical DFD For Encashing Cheque

Customer

ClerkVerify A/CSignatureUpdateBalance

CashierVerify Token

Take Signature

Cash

Cheque Cheque withToken numberToken

Token

Entry inDay Book

Store chequesBad Cheque

Customer Accounts


Logical DFD For Cheque Encashment

RetrieveCustomer

Record

CheckBalance,

Issuetoken

StoreToken no& cheques

Search& match

token

UpdateDaily

cash bookCustomer

Day bookCashToken Slip

Cheque withtoken

ChequeCheque with

Token

Cheque Customer accounts

Cheque storeWith token no.

Token SlipOr cheque

System Analysis and Design/ Structured systems analysis and design Learning Objectives

Learning Objectives

In this module we will learn

How to use structured English to precisely specify processes The terminology used in structured English Terminology of decision tables and how it is used to specify complex logic

How to detect errors in decision table specifications Terminology and use of decision trees Comparison of structured English, decision tables and decision trees


System Analysis and Design/ Structured systems analysis and design Motivation

Motivation

Before designing a system an analyst must clearly understand the logic to be followed by each process block in a DFD

An analysts understanding must be cross checked with the user of the information system.

A notation is thus needed to specify process block in detail which can be understood by a user.

Notation used must be appropriate for the type of the application to be modeled. Different notations are needed to represent repetition structures,complex decision

situation and situations where sequencing of testing of conditions is important

For complex logical procedures a notation is needed which can also be used to detect logical errors in the specifications.

A tabular structure for representing logic can be used as a communication tool and can be automatically converted to a program.



Process Specification

Once a DFD is obtained the next step is to precisely specify the process.

Structured English, Decision tables and Decision Trees are used to describe process.

Decision tables are used when the process is logically complex involving large number of conditions and alternate solutions

Decision Trees are used when conditions to be tested must follow a strict time sequence.


Structured English

Structured English is similar to a programming language such

as Pascal

It does not have strict syntax rules as programming language

Intention is to give precise description of a process

The structured English description should be understandable

to the user


Structured Englishif customer pays advance

then Give 5% Discountelse

if purchase amount >=10,000then

if the customer is a regular customerthen Give 5% Discount

No Discountelseend if

else No Discount end if

end if


DecisionTable-example

Same structured English procedure given as decision table

CONDITIONS RULE1 RULE2 RULE3 RULE4Advance payment made Y N N NPurchase amt >=10,000 - Y Y N

Regular Customer? - Y N -

ACTIONS

Give 5% DiscountGive No Discount

X X - -- - X X


DecisionTable-explanation

Conditions are questions to be asked

Y is yes,N is no & - is irrelevant

A X against the action says the action must be taken

A - against the action says the action need not be taken

Rule 2 in decision table DISCOUNT states:

if no advance payment and purchase amount >=10000and regular customer then give 5% discount


Structured English

Imperative sentences- Actions to be performed should be

precise and quantified

Good Example: Give discount of 20%

Bad Example: Give substantial discount


Structure English (Contd.)

Operators -Arithmetic : +, -, /, *

Relational : >, >=,


DecisionTree-example

The structured English procedure given in 6.1.3 is expressed as a Decision tree below

Give 5% Discount

C1

C2

C3Y

Y

Y

N

N

N

Give 5% Discount

No Discount

No Discount

C1: Advance payment madeC2: Purchase amount >=10,000C3: Regular Customer

Y = YesN = No


StructuredEnglish-decision Structures

If conditionthen

{ Group of statements }else

{ Group of statements }end if

Example: if(balance in account >= min.balance)then honor requestelse reject request

end if


StructuredEnglish-case Statement

Case (variable)Variable = P: { statements for alternative P} Variable = Q: { statements for alternative Q}Variable = R: { statements for alternative R}None of the above: { statements for default case}

end case

Example : Case(product code)product code =1 : discount= 5%product code =2 : discount =7%None of the above : discount=0

end case


STRUCTUREDENGLISH-REPETITION STRUCTURE

for index = initial to final do{ statements in loop }

end for

Example : Total =0for subject =1 to subject =5 do

total marks=total marks +marks(subject)write roll no,total marks

end for


STRUCTUREDENGLISH-WHILE LOOP

while condition do{ statements in loop }

end while

Example : while there are student records left to doread student record

compute total marksfind class

write total marks, class, roll noend while


Example

Update inventory file

for each item accepted record do{ search inventory file using item code

if successfulthen { update retrieved inventory record;

write updated record in inventory file using accepted record}

else { create new record in inventory file;enter accepted record in inventory file}

end ifend for


Decision Table-motivation

A procedural language tells how data is processed

Structured English is procedural

Most managers and users are not concerned how data is processed-

they want to know what rules are used to process data.

Specification of what a system does is non-procedural.

Decision Tables are non-procedural specification of rules used in

processing data


Advantages Of Decision Table

Easy to understand by non-computer literate users and managers

Good documentation of rules used in data processing.

Simple representation of complex decision rules .


Advantages OF Decision Table (Contd.)

Tabular representation allows systematic validation of specification detection of redundancy,incompleteness & inconsistency of rules

Algorithms exist to automatically convert decision tables to equivalent computer programs.

Allows systematic creation of test data


Method Of ObtainingDecision Table From

Word Statement Of RulesEXAMPLE

A bank uses the following rules to classify new accounts If depositor's age is 21 or above and if the deposit is Rs 100 or more, classify the account type as A If the depositor is under 21 and the depositis Rs 100 or more, classify it as type B If the depositor is 21 or over anddeposit is below Rs 100 classify it as C If the depositor is under 21 anddeposit is below Rs 100 do-not open account

Identify Conditions: Age >= 21 ClDeposits >= Rs 100: C2

Identify Actions : Classify account as A, B or C Do not open account


Decision TableFrom Word Statement

CODITIONS Rule 1 Rule 2 Rule 3 Rule 4C1 : Age >= 21 Y N Y N

C2: Deposit >=100 Y Y N N

ACTIONS

A1: Classify as A X - - -

A2: Classify as B - X - -

A3: Classify as C - - X -

A4: Do not openAccount - - - X

Condition Stub

Action Stub


Decision TableNotation Explained

ACTION ENTRIES

CONDITION ENTRIESCONDITION STUB

ACTIONSTUB

RULE

4 Quadrants-demarcated by two double linesCONDITION STUB LISTS ALL CONDITIONS TO BE CHECKEDACTION STUB LISTS ALL ACTIONS TO BE CARRIED OUTLIMITED ENTRY DECISION TABLE:ENTRIES ARE Y or N or -.Y-YES,N-NO,-IRRELEVANT(DONT CARE)X against action states it is to be carried out.-against action states it is to be ignored.Entries on a vertical column specifies a rule


Decision Table Notation -Contd

ORDER OF LISTING CONDITIONS IRRELEVANTi.e. CONDITIONS MAY BE CHECKED IN ANY ORDER

ORDER OF LISTING ACTIONS IMPORTANT

ACTIONS LISTED FIRST CARRIED OUT FIRST

SEQUENTIAL EXECUTION OF ACTIONS

RULES MAY BE LISTED IN ANY ORDER


InterpretingDecision Table-else Rule

C1: Is applicant sponsoredC2: Does he have min

qualificationC3: Is fee paid?

X - -

Y Y

Y N

A1: Admit letterA2: Provisional Admit

letterA3: Regret letter

Y Y

- X -

- - X

R1 R2

ELSE


Interpreting Decision Table-else Rule (Contd.)

Interpretation R1: If applicant sponsored and he has minimum qualificationsand his fee is paid Send Admit letter

R2: If applicant sponsored and has minimum qualifications and his fee not paid send provisional admit letter

ELSE: In all cases send regret letter.The else rule makes a decision table complete


Decision Table For Shipping Rules

C1: Qty ordered


Extended Entry Decision Table

Condition Entries not necessarily Y or N Action entries not necessarily X or - Extended Entry Decision Tables(EEDT) more concise EEDT can always be expanded to LEDT

C1 : Product code 1 1 1 1 1 2

C2 : Customer code A B A B C -

C3 : Order amount 500 - -

Discount = 5% 7.5% 7.5% 10% 6% 5%

R1 R2 R3 R4 R5 R6Example


Mixed Entry Decision Table

Can mix up Yes, No answers with codes

Rl R2 R3 R4 R5 R6

Cl : Product code = 1? Y Y Y Y NC2: Customer code = A B A B C -C3: Order amount < 500? Y Y N N - -

Discount = 5% 7 5% 7 5% 10% 6% 5%

Choice of LEDT, EEDT, MEDT depends on ease of communication with user,software available to translate DTs to programs, ease of checking etc.


Linked Decision Table

Salary point=6 N eConduct OK? Y lDiligence OK? Y sEfficiency OK? Y e

Go to table 2 X -No promotion - X

Decision table 1

Salary point>2 N N N Y 1 yr as class 1 Y N - -

officer Departmental test Y - N -Passed?

Decision table 2

Advance to next salary pointNo promotionGo to Table3

X - - -- X X -

- - - X


Linked Decision Table

Decision table3

1.Observe that one can branch between tables

2. Whenever complex rules are given it is a good idea to break them up into manageable parts

Complete departmentalCourse1 yr since last increment

Yelse

Y

Advance to next salarypointNo promotion

X -

- X

14


Logical Correctness Of Decision Table

Consider decision table DTI:

Rl R2Cl: x>60 Y .C2:x


Logical Correctness Of Decision Table (Contd.)

A decision table with 1 condition should have 2 elementary rules Each elementary rule must be distinct Each elementary rule must have distinct action If a decision table with k conditions does not have 2k rules specified

it is said to be incompleteFor example : DT2 does not have the elementary rule C1:N,


Logical CorrectnessOf Decision Table (Contd.)

C2:N.

It is thus incomplete.

If the decision table has the same elementary rule occurring more than once it is said to have multiplicity of specifications

For Example:In DT2 The rule C1:Y,C2:Y occurs twice.Thus it has multiplicity of specification



If action specified for multiple identical rules are different then it is called ambiguous specifications

DT2 has an ambiguity.Rules R11 and R21 are identical but have different actions

Ambiguity may be apparent or real



If an apparently ambiguous specification is real then it is a contradiction

For example : If C1:(X > 60) = Y and C2:(X > 40) = Y then X = 70 will satisfy both inequalities.

As two actions are specified for (Cl = Y, C2 = Y) and they are different the rule is really ambiguous and is called Contradictory Specification.



If all 2k elementary rules are not present in a k condition decision table is said to be incomplete.

DT2 (PPT 6.3.1) is incomplete as rule C1:N, C2:N is missing

Rule C1=N, C2:=N is logically possible as C1=N is X= 40. A value of X = 50 will make C1=N,C2=N



Thus DT2 has a real incomplete specification

A decision table which has no real ambiguities or real

incompleteness is said to be logically correct

A decision table with logical errors should be corrected


Use Of Karnaugh Maps

KARNAUGH map abbreviated K-map is a 2 dimensional diagram with one square per elementary rule

The k-map of DT2 is

? Al

A2 A1,A2

If more than one action is in one square it is an ambiguous rule

If a square is empty it signifies incomplete specification

C2C1

N

Y

N Y


Use Of Karnaugh Maps

Structured English procedure:

If carbon content50

then if tensile strength>30000then steel is grade 10else steel is grade 9

end ifelse steel is grade 8end if

else steel is grade 7end if


Use OfKarnaugh Maps

Decision table-Grading steel

C1:Carbon content 50C3 tensile strength>30000

Y Y Y N Y N N NY Y N N N Y Y NY N N N Y Y N Y

Grade 10 9 8 7 ? ? ? ?


KarnaughMaps Grading Steel

7 ? 9 8

? ? 10 ?

C3C1 C2

N

Y

NN NY YY YN

The 3 conditions are independent The decision table is thus incomplete Observe that in the Structured English specifications

the incompleteness is not obvious


Decision Table-Arrears Management

R1 R2 R3 R4 R5 R6

C1:Payment in current month Y N N - - ->min.specified paymentC2:Payment in current month>0 - Y Y - N NC3:Any payment in last 3 months - - - N Y YC4: Actual arrears > 3(min.Specified payment per month) - Y N Y N Y

A1 : Send letter A X - - - - -A2 : Send letter B - X - - - -A3 : Send letter C - - X - - -A4 : Send letter D - - - X - X A5 : Send letter E - - - - X -

1


Karnaugh Map

? A3 A1 A1*

A4 A2A4+ A1A4+ A1A4*

A4 A2 A1 A1A4*

A5 A3 A1 A1A5*

NN NY YY YNNN

NY

YY

YN

C3C4C1C2

K Map for decision table


Karnaugh Map

C1 : x>m C2:x>0 C3:y>0 C4:z>3m m>0

C3,C4 independent of C1,C2 C1,C2 dependent

C1: Y C2: Y x>m, x>0 possible

C1: Y C2: N x>m, x


Karnaugh Map

C1: N C2: N x


Correct Decision Table

If users say that for rules C1C2C3C4:NYNY AND NYNY(marked with + in k-map) the action is A4 and forC1C2C3C4:NNNN also it is A4, the corrected map is

NN NY YY YN

A4 A3 A1

A4 A4 A4A4 A2 A1A5 A3 A1

NN

NY

YY

YN

C3C4

Date post:	29-Sep-2015
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