Developing Information Systems Chapter 11

Methodology - CASE l Methodology - way of working decided on within a company - method + techniques - follow-up by project leader l CASE computer assisted software engineering - software package based on repository - upper-case + lower case System Development Life cycles

Waterfall model project definition system study design programming Installation Post Imple- mentation Project proposal report System proposal report design specifications program specifications code system performance tests audit, feed-back Waterfall model Spiral model Whirlpool model Rugby model - intermediate reports - go/nogo intervals

Boehm’s Spiral Model prototype 1 prototype 2 operational prototype Risk Analysis Risk Analysis Risk Analysis determine objectives, alternatives constraints evaluate alternatives identify, resolve risks simulation modelsBenchmarksrequirements plan life cycle plan concept of operation Software design Design validation and verification integration tests and plan detailed design coding integration tests implementation progress through steps Plan next phases Prototype based

Whirlpool model project definition system study design programming Installation Post Imple- mentation Project proposal report Functional specifications Feasibility report design specifications program specifications code system performance tests audit, feed-back After each phase a quick review of the previous phases is made

OO-life cycle With the increasing complexity of the systems, the waterfall model suffers from two illusions:  The analyst knows everything and understands the problem completely before implementation starts  The users read the system analysis report and approve it

OMG-model (Object Management Group ) Facts:  System requirements are not fully known at the start  knowledge of the system grows during development  better develop a system incrementally  start with some core functions object modelling analysis design construction full system definition coordination and reuse

OMG Project Management  Iterative style develop a series of solutions to a problem, each of them closer to satisfying the requirements ( also called : evolutionary development )  Incremental style Builds system functionality a little at a time. The results are not entire solutions. Matthew Pittman proposes iterative analysis and design combined with incremental development Problem is managing the reuse (by design, not by accident) How can such a project be estimated, tracked, controlled

The waterfall model

Waterfall model project definition system study design programming Installation Post Imple- mentation Project proposal report System proposal report design specifications program specifications code system performance tests audit, feed-back Waterfall model Spiral model Whirlpool model Rugby model - intermediate reports - go/nogo intervals

Project definition What do we want to accomplish ? - solve a new problem - incorporate new requirements - improve existing system Is a new system the best solution ? Who will be involved ? Organizational problem

System study : functional specs Objective: What is the problem ? Responsibility: The user Execution: Top-down technique 1.Activities: just a few sentences 2.Logical operations ( processes): for each activity 3.Details and definitions: rules, actions, controls, forms 4. Detail information: object, units, begin and end, classes, names

System study : functional specs 2 The problem definition report includes: For the input: For the output: Furthermore:. form. point of time and frequency. origin. responsibility. type and layout. point of time and frequency. destination. usage. reasons for realization. financial advantages. constraints and borders of the system

System study : The feasibility study Responsibility from this phase on in the ICT-department. study of the existing system. borders of the new system. links with other systems. study of different solutions. division in subsystems. applicability of packages. estimation of personnel requirements. cost-benefit analysis The report allows the steering committee to: - fix timings - final decision

Design : general l What must be done to solve the problem?  data flow diagrams / use cases  inventory of the data elements  data dictionary  logical model of the system ( data analysis, UML)  major algorithms l compose the working groups l planning per department

Design : Detailed - interfaces with other systems - controls and checking - privacy and security aspects - hardware specifications - job flow diagrams - Physical database design - high-level program design Detailed system and design specification

Programming and Implementation l Program design  diagrams  code  tests l documentation l data conversion l procedure development l user training - Program specifications - Code - Program specifications - Code

- User documentation - Operations documentation - User documentation - Operations documentation Installation l Installation of the hardware l Install security procedures l Tests in operational environment l Training operations department l Take-over in user department and IT- department l Operational

Post-implementation AUDIT - compare actual system with projected budget and timing - evaluate actual operation cost - evaluate user satisfaction - evaluate security MAINTENANCE - establish hardware maintenance procedures - test security plan - establish change management procedures

Prototyping Alternative system analysis and building technique Advantages  better interaction with user and higher involvement  the technique invokes more requirements  additional system life cycle Disadvantages  expensive tools ( 4GL )  user must well understand the aim of the prototype  more skills required from analysts and programmers  documentation often neglected

Software packages. Where functions are common to many companies. Where in-house data processing resources are in short Advantages: > development bottleneck can be avoided > experience and knowledge are bought with the programs > vendors supply tools and assistance > mostly better documented Disadvantages: > company reorganization needed, other working methods >conversion and customization effort needed

DFD - Example Client Publisher BooksBooks clients Pending orders publisher orders AC receivable AC payable control orders Create publisher orders Assemble Client orders Deliveries against pending orders control deliveries Payment against invoice Create invoice Create Publisher order control invoice Order Valid orders assembled orders publisher orders delivery Client invoicer payment individual orders titels quantities Publisher payments invoice copy delivery Consignment note control copy

Use Case Diagrams Trading Mgr Trader Accounting system Salesperson Capture deal Limits Exceeded Capture Deal Price Deal Analyze Risk Set Limits Valuation Update Accounts Actor Use Case “uses” Example : “extends”

Class Diagram:Typical example Order dateReceived Is prepaid number:string price: Money Dispatch( ) Close( ) Customer Name Address CreditRating : string Personal Customer CreditCard# Corporate Customer contactName creditRating creditLimit Remind ( ) billForMonth Order Line Quantity:int Price:Money IsSatisfied Employee Product * 1 Multiplicity mandatory Association Generalization Class Constraint 1 (If Order.customer.creditRating is “poor” then Order.isPrepaid must be true) * Line items Role Name Multiplicity: many-valued 0..1 * Multiplicity: optional * 1 Sales rep. {creditRating() ==“poor”}