CS 634 Information Systems Dr Deepak B Phatak Subrao Nilekani Chair Professor Kanwal Rekhi Building, Department of CSE IIT Bombay Session 8, Software Engineering,

CS 634 Information Systems

Dr Deepak B PhatakSubrao Nilekani Chair Professor

Kanwal Rekhi Building, Department of CSEIIT Bombay

Session 8, Software Engineering, SRS

IIT BOMBAY

cs634-Session 8, Software Engineering, SRS Dr. Deepak B Phatak 2

IIT BOMBAY

SESSION OVERVIEW

• Principles of Software Engineering• Software Engineering Activities• Process Maturity Measures• Review of ER Model• Functional Model

• Data Flow Model

• User Interface Issues• Software Requirement Specifications (SRS)


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ROLE OF SOFTWARE

• Business Functionality Depends Mainly On Software

• Good Systems S/W Is The Basis• OS, Programming Languages (3GL)

• Tools To Build S/W Keep Evolving• 4GL (SQL), RAD Tools

• Typical Life Cycle: 10 -15 Years


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Software Characteristics

• Software is Developed or Engineered• Not Manufactured

• Software Does Not “Wear Out”• May Become Un-Maintainable• Hardware Does wear out

• Most Software is Custom-Built• Limited Role for Packaged Products Which Need

Customization and Integration With Other Apps.


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SOFTWARE ENGINEERING

• Application of a systematic, disciplined, quantifiable approach to the development, operation and maintenance of software; i.e., The application of engineering to software• IEEE Definition 1993


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SOFTWARE ENGINEERING

• Engineering is the analysis, design, construction, verification and management of technical (or) social entities

• To engineer S/W, we must define A development process


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Building Information Systems

• Functional Specifications• System Engineering

• Feasibility Study• Allocation To H/W, S/W, People

• System Analysis• System Design• Coding, Testing, Integration• Acceptance and Deployment


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Software Process Models

• Linear Sequential Model• The Waterfall Model • User Knows Inadequacies Too Late

• Prototyping Model• Model Business, Data, and Processes• Generate Application• Test and Turnover


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Software Process Models

• Rapid Application Development • Evolutionary Models

• The Incremental Model• Sequential + Prototyping

• The Spiral Model

• Concurrent Development Model• Formal Methods Model


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UMBRELLA ACTIVITIES

• Project Tracking And Control• Formal Technical Reviews• S/w Quality Assurance• Configuration Management• Document Production• Reusability Management• Measurement, Risk management


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Software Project Management

• Basic Project Management• Software Teams

• Coordination & Communication

• Process and Project Metrics• Based on Lines of Code (LoC)• Function Point Oriented

• Project Scheduling and Tracking


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Software Engineering

• A Quality Focus• Process• Methods• Tools


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SEI MODEL

• Software Engineering Institute• At Carnegie Mellon University

• Capability Maturity Model• Five Levels of Maturity to Measure

Effectiveness of an Organization in its Software Development Practices (CMM levels)


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CMM LEVEL 1 (Initial)

• Process is Ad Hoc (Even Chaotic)• Very Few Processes Are Defined• Success Depends Entirely On Individual Efforts


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CMM LEVEL 2 (Repeatable)

• Basic Management Processes Are Established

• Cost Schedule And Functionality Is Tracked

• Discipline To Successfully Repeat Projects With Similar Applications


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CMM LEVEL 3 (Defined)

• Software process for both management and engineering activities is standardized, documented, and integrated across the organization

• All projects use the documented approved version


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CMM LEVEL 4 (Managed)

• Detailed measures of process and product quality are collected

• Process and products quantitatively understood and controlled using detailed measures


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CMM LEVEL 5 (Optimizing)

• Quantitative feedback exists from process for continuous process improvement

• Testing innovative ideas and technologies


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Classical Analysis Modeling

• Data Object Description• Entity Relationship Diagram

• Relational Model

• Process Specification• Data Flow Diagram

• Control Specifications• State Transition Diagram


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SYSTEM ANALYSIS

• Represent Information Domain Of The Problem• Which Data, How Manipulated• Five Ws and One H

• Understand S/W Requirements• Specify S/W Functions, Interfaces, Constraints


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sroll

ENTITY MODEL

Student

sname

shostel sroom scpi

scourses

shobbies


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ccode

Course Entity

Course

cname cstudents

cfaculty

ccredits


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TABLE REPRESENTATION

sroll sname shostel

99011012 Vijay Ambre 02

sroom

01D15034 Shaukat Ali 08

scpi

218 8.497.94218


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TABLE REPRESENTATION

ccode cname ccredit

CS634 Information Systems 06

CS101 Computer Programming 06


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RELATIONSHIPS

Student

Registers For

Course

sroll

ccode

Grade


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The REG Table

TABLE FOR RELATIONSHIPS

sroll ccode grade

99011012 CS402 AB


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ER MODEL

• Captures Static Characteristics• Associations May Be

• One To One (Shown By A Dot)• One To Many, Many To One

• Easy To Map The Structure To Files Or Data Base Schema

This Model Does Not Cover Dynamic Features, Workflow, Interfaces, etc.


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DATA DICTIONARY (Entity Sets)

• A Repository Of All Information About Entities And Associations

• For An Entity• Name, Brief Description• Approximate Number in The Set• Frequency of Changes• Any Other Information


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DATA DICTIONARY (Attributes)

• For Each Attribute• Name, Brief Description• Data Type and Field Width• Valid Values (Domain)• Typical Values


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FLOW MODELING (DFD)

• As information flows through A system, it is transformed

• A transformation represents part of a system function

• Such flow and the attendant transformation can be captured using a model for data flow

• Represented using data flow diagrams


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Example of a Data Flow

Participant

Enrollment-master

Reg-form

Acct-masterRoll-list

Pnext

ErrorListValidate

Registration

Faculty


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Example of a Data Flow

Participant

Enrollment-master

Reg-form

Acct-masterRoll-list

Pnext

ErrorListValidate

Registration

ValidationInformation

DF1

Faculty


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DFD SYMBOLS

External Entity

Data Flow

Donor

Acct-statement

ProcessCheckExpense

Data-StorePledge-Info


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DFD SYMBOLS

• External Entity: Source Or Consumer Of Information

• Arrow: Represents Flow of Data• Process: Describes Transformation

• Ultimately, Represents the Algorithm or Program That Gets/Puts Data From/To Arrows and Contains Processing Specifications

• Store: Stores Data


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DFD Data Dictionary

• Each Symbol Must Have An Associated Label

• Data Dictionary Entries Must Define That Label in Terms Of its Meta-Data

• Process Narrative (PSPEC) Must be Included


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Example Entries

• Reg-Form• Roll Number, Name, Course, Audit/Credit, Time-

table slot, …

• Validation-Information• Input to Store: Roll-number• Return From Store

• Name, CPI, fees-payment status, …


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CONTEXT DIAGRAM

• Called level 0 DFD, or the fundamental system model

• Single bubble with incoming and outgoing arrows mainly showing the entities involved

• Functional partitioning further done to derive several level 1 DFDs


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Context Diagram Example

CDEEPSYSTEM

Participant-Info

Course-Info

Faculty-Info

Remote-Centre-Info

Participant-Grades

Course Contents

Annual Revenue


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REFINEMENT

• Expansion Of a Level 1 DFD To Add Detailed Processes

• Flow Continuity Necessary• Expansion Must Have Same I/O


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USER INTERFACE

• Modeling Interactive Screens• Capture And Validate Input• Query Retrieval

• Modeling Reports• Contents and Format• On Screen, On Printer

• Special Interfaces


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USER INTERFACE

• Screen And Forms Layouts• Source And Target Stores• Operational Considerations

• Ease Of Use (User Friendliness)• Keystroke Minimization


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SRS Document (Draft Contents)

• Introduction• Functional Specifications• Data Models and Data Dictionary

• ER Model• Data Flow Model

• User Interface Requirements• Interfaces to Other Systems• Procedures and Workflow• Acceptance Criteria• Appendices

Documents

CS 634 Information Systems Dr Deepak B Phatak Subrao Nilekani Chair Professor Kanwal Rekhi Building, Department of CSE IIT Bombay Session 8, Software Engineering,