Data Modelling

 

PAMS BUISNESS

Outline

Outline:

  Data model   Decision tables





  Checking the logical design   Test Strategy





Purpose: As we Model the logical system to meet the requirements, we have several techniques to use.

         



Several modelling tools that can be used:



Use case model



Data flow diagrams



Data model



Decision tables

Data Model: Put requirements gathered needed for the system, put these into a

  Case Model



Need to analyse requirements from fact finding

  eg interviews



Need to model the data stores outline what does in them Whats in a DATA STORE:

  Anything we need ti know (must be relevant) o  Things the processes work on Books o  Dinner orders o  o  Railway ticket requests



1

 

  Info needed by processes: Title, author, desc, price etc o  Order number, table number, menu items etc o  o  Passenger name, start station, dest



These are all requirements from analysis

Data Modelling Overview:

  Data modelling gives us shape of what goes in Data Stores o  Data stores in a computer system are the tables of its database

o

Questions to Ask when modelling the Data:

  What things is the system dealing with? What do we know about the things? o  o

  How are the things linked together?

o

What things is the system dealing with?

The things the system deals with are the things that are relevant:

  Books, Modules, Status o  Ticket requests, tickets, passengers Vehicles, drivers, service records o 

o

They become the entities in a data model and the tables in a Database:

  Books, Modules, Status Request, Ticket, Passenger o  Vehicle, Driver, Service o 

o

What do we know about the things?

Characteristics or details we record

  Title, author, module name, module code o  Ticket number, date travel, request date, address o  Vehicle number, make, driver name, service date

o

2

 

Characteristics we call attributes, they become fields or columns in a Database table

  Title, Author, ModuleName, ModuleCode TicketNo, TravelDate, RequestDate, Address o  o  VehicleNo, Make, Driver, ServiceDate

o

How are the things linked together?

  How do they relate? Books link modules o  o  Books link to status o  Vehicles link to drivers Vehicle link to services o  o  Passengers link to requests o  Tickets link to requests The links are called Relationships o  o  Help the system to find the right info in right Database

o

Data Model for System: Consists or ERD

BOOK

MODULE

STATUS

.. and the Tables to be used in the database

  Table names and attributes o  Book (BookNo, Title, Author, Description, Price)

o

3

 

Data model summary:

  Data model is part of the logical for system Shows things that are relevant r elevant to the system, called entities o  o  Shows what details are needed about the things, called attributes o

Structures English:

  o  o  o  o

One way of describing steps in carrying out a process Can be used as part of Use Case Description Describes the logic of a business process Looks similar to pseudocode… 

  Pseudocode describes the logic in a piece of code

o

  Clear and unambiguous

o

Structured English – BASICS:

  Threes rules o  Use the four constructs   Sequence   Selection   Iteration   Case Indent to make it clear which statements go together o  o  Limit the vocabulary   Standard words and commands   Names of entities and attributes from data model

o













Structured English – SUMMARY

  Describes logic of business process Simple language constructs o  o  Clear and Unambiguous

o

Decision Tables:

  o  o  o  o

Shows what actions should be taken in different combinations of circumstances Clear and unambiguous way of specifying what to do Can be used as part of use case description Not always a lways needed Very useful when complex decisions need to be made and acted on

4

 

Decision tables – BASICS

  Conditions One-or-other questions o  o  EG YES / NO o  Rules Combinations of answers to Questions o  o  Actions o  What will happen each case Decisions o  Which actions apply to which rules ie in which circumstances o 

o

Decision tables – BUILDING To build Decisions Table:

  ID Conditions   Write most important one first ID possible actions o    Write most frequent one first o  Work out the rules ie combinations of conditions   Combinations of Y/N   2 conditions give 4 rules, 3 conditions give 8 rules etc o  Record which actions are relevant to each rule   Put an X in that box of the decision table Check you have all the rules o    Combinations of Y/N o













Decision tables –  EXAMPLE To calculate ticket fares Conditions: Concession (child, senior), return ticket Actions: No discount, 10% discount, 50% discount

Concession Return No Discount 10% Discount 50% Discount

Y N

N Y

Y Y

X X

X

5

N N X

 

Decision tables – SUMMARY

  Decision table summaries what happens in combinations of circumstances Shows o  o  Conditions o  Actions Rules o  o 

o

Decisions

Checking the logical model:

  We have now put together the logical model Use Case Model for Process outline o  o  Data flow diagrams for process breakdown o  Data model for data requirements Structures English for process logic o  o  Decision table for combinations of circumstances

o

How to check the logical model:

  Go back to people you talked to when doing the detailed fact finding

o

  o  o  o  o 

o

Bring requirements specification along Go through all the diagrams and models with them Check understanding Get any corrections Revise diagrams and models

  This can take time but worth it Any mistakes found at this stage can be easily corrected o  o  Anything found later is harder to correct

o

Designing the test strategy: stra tegy can be designed   One logical model approved, test strategy Users may be involved for testing o  System testing o  o  User acceptance testing

o

6

 

  Agree with users o  Who will write cases o  Who will write test scripts scri pts / expected results Who will carry out tests o  Who will analyse test results o  o  Joint effort between devs and users

o

Inputs to test strategy:

  Test Strategy based on: o  Requirements o  Use case model Data flow Diagrams o  Data Model o  o  Structured English Decision Tables o  o  End-to-end operation o  A System can process info from initial input to final output o  Eg input a book and follow it through it purchase

o

Unit Testing:

  o  o  o  o 

o

Unit testing part of System Construction Tests program code and access Database Unit tests plans typically written when program logic being developed Task for developers Users do not get involved

Test Strategy Summary:

  Test strategy and test cases written based on logical system design Tests are carried out after system has been developed o  o  Testing is Team Effort with Developers D evelopers and Users o

7