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Posts tagged ‘o-o’

History of programming languages

ENIAC Electronic Numerical Integrator And Computer (1946)

The first using of programming, although cables were connected to ports to achieve this.

UDSAC (1947)

First computer with memory

FORTRAN (1954-57)

The first language with a compiler, this cut programming time from 2 weeks to 2 hours

GOTO statements

These are bad for programming, they organise the program in a way that makes it almost impossible to debug.

Object-Orientated

The data and its processes are kept as a single unit called an object

Declarative languages

The computer is told what to do, not how to do it such as SQL

Constraint based languages

Conditions need to be met before processes will be executed

 

Programming language generations

First generation – Machine code (0’s and 1’s)

Second generation – Assembler (Mnemonic codes)

Third generation – Modern programming languages (BASIC, C and PASCAL)

Forth generation – Declaritive languages (SQL etc. code tells computer what, not how to do it)

Fifth generation – Constraint based languages (Prolog, artificial intelligent applications)

 

 

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.

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