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Archive for March, 2011

O-O

O-O contains:

UML

Attribute

Methods

Messages

Classes

Instances

Parents contain:

Objects – These stay within a class

Attributes – The characteristics that stay within the obects

Methods – Tasks that can be applied

Instances – Examples of attributes and methods

Eg. Attribute dog

Method Eat, Sleep, Bark

Instances If the dog sees food it will eat

Modelling types

Data flow diagrams (DFD)

O-O modelling

Uses UML (a case tool), attributes, methods, messages, classes and instances.

Each object needs a parent object

DFD has different levels as follows:

  • Context level diagram
  • Level 0 DFD
  • Level 1 DFD
  • Level 2 DFD

There should be no more than four levels, (the context level diagram counts as a level even though it doesn’t have a number)

Context level diagram contains:

  • The processes of a system
  • External entities
  • Data flow in and out of the system
  • The relationship between dataflows

Level 0 DFD contains:

  • Processes of the system
  • External entities
  • Data flows
  • Data stores
  • Sub processes

Level 1 DFD contains:

  • Subprocesses of the level 0 DFD

Level 2 ERD (Entity Relationship Diagram) contains:

  • Entities
  • Relationships
  • Cardinality – The closest option to the box
  • Optionality – May have this, option furtherest away from the box

Cardinality

0 – Zero

1 – One

<-   – Many (more like an E)

Optionality

0 – Zero

1 – One

*ERD’s should have the cardinalities and optionalities written out for both directions

The context level provides each item/process, in level 0 these are numbered eg 1. 2. 3. etc

In level one each subprocess is numbered off of its original process eg. 1.1, 2.1, 3.2 etc

In level two these processes are broken down again eg 1.1.1, 2.1.3, 3.2.2

UML

Unified modelling language used mostly for o-o

Contains a super class, a class and a subclass

Visual modelling is a UML

UML diagrams use:

  • A use case diagram
  • Activity diagrams
  • Sequence diagrams
  • Class diagrams
  • State transitional diagrams

Objects are held within the classes Eg.

Class

| Object

| Object

| Object

| Object

————

The relationship is the information the objects need to know about each other, or how they relate.

SDLC Methodologies

Waterfall – Only method which doesn’t allow iteration (Going back and fixing things)

Semistructured

Structured -Need good multi-tasking skills to keep up with this one

SSADM

Prototyping

(Inbetween these two is incremental development)

RAD

O-o

SDLC

System development life cycle

There are two types of SDLC the 4 stage and the 6 stage

Note that in the six stage SDLC some of the steps fit into the four stage

4 stage

1.Plan

2.Design

3.Development

4.Implement

6 stage

1.Prelimenary investigation

1.Analysis

Design

Development

4.Implementation

4.Maintainance

A system has an SDLC which uses different methodologies such as waterfall, rad, prototype or o-o, it is made in three phases

Phase one – The initial investagation

  • Feasibility study
  • Estimate
  • Roles/ organisation chart
  • Scope
  • Recommendations

Phase two – Requirement modelling

  • Data flow diagram (DFD)
  • o-o Modelling (using the case diagram)

Phase three – Design

  • System design specification

JAD and RAD

JAD is the method used to get information to define what is needed and wanted for the system

RAD is a method where proto types are built and assessed by the client as the system is being built.

Fact finding plans

You need information to put together a plan, the following questions help put this plan together

Who, What, Where, Why, When and How

What is being done and what should or could be done?

Logic symbols

¬ = Not

Λ = And

V = Or

They are used in this in  equations

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