Class Diagram#

Class diagrams clearly map out the structure of a particular system by modelling its classes, attributes, operations, and relationships between objects [Lucidchart, 2017].

Class diagrams are particularly useful when using Object Orientated Programming.

The standard class diagram is composed of three sections:

  • Upper section: Contains the name of the class. This section is always required.

  • Middle section: Contains the attributes of the class. Use this section to describe the qualities of the class.

  • Bottom section: Includes class operations (methods). Displayed in list format, each operation takes up its own line.

[Lucidchart, 2019]

Class Diagram Symbols#

class symbols

Checking the Class Diagram

When marking a Class Diagram the following questions are asked:

  • Are all the code’s classes represented?

  • Does the diagram’s attributes match the variables in the class’ __init__ method?

  • Does the diagram’s methods match the class’ methods?

Summary#

class diagram summary poster

Unit 1 subject matter covered:

  • Symbolise algorithms and interrelationships with sketches and diagrams [QCAA, 2017]

Unit 2 subject matter covered:

  • Symbolise well-ordered and unambiguous algorithms using pseudocode for procedural code that processes data for insertion into a database or manipulates or displays retrieved data

  • Symbolise well-ordered and unambiguous algorithms using pseudocode for user interaction, data validation and data presentation [QCAA, 2017]

Unit 3 subject matter covered:

  • Generate a conceptual model of a possible solution by applying systems thinking that identifies system boundaries, properties, inputs and outputs, user interface, system controls

  • Recognise and describe program components such as objects, event handlers and multimedia assets [QCAA, 2017]

Unit 4 subject matter covered:

  • Symbolise and explain how application sub-systems, e.g. front end, back end, work together to constitute a solution [QCAA, 2017]