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Posts tagged ‘Class’

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


0 – Zero

1 – One

<-   – Many (more like an E)


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


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.


| Object

| Object

| Object

| Object


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

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