UML class diagram

Definition[edit | edit source]

UML Class diagrams are one kind of official diagram types of the Unified modeling language (UML). They describe the structure of a system.

“If someone were to come up to you in a dark alley and sy, "Psst, wanna see a UML diagram?" that diagram would probably be a class diagram.”(Fowler, 1993:35).

“A class diagram describes the types of objects in the system and the various kinds of static relationships taht exist amoung them. Class diagrams also show the properties and oprations of a class and the constraints that apply to the way objects are connected. The UML uses the term feature as a general term that covers properties and oprations of a class.” (Fowler, 1993:35).

Architecture[edit | edit source]

Class diagrams are made with quite a complex "language". Here are some elements (I know I have to go over this - Daniel K. Schneider 16:45, 5 June 2007 (MEST))

Classes

• Classes are represented with boxes
• Represented by: a rectangle with one, two or three "fields": classname, properties (attributes) and operations.
• Properties are structural elements of class. Now it get's a little bit complicated. You can describe a property either with an attribute (i.e. within the class box) or with an association (see below).

Association

• A relationship between two classes or properties
• Represented by: a solid line, or if directional with an arrow directed from the source object to the target object, or if bidirectional with an arrow on both ends.

Aggregation

• A part-of relationship
• Represented by: a solid line, with an emtpy lozange at aggregation end and arror at member end
• Example: a learning object is part of an environment

Generalization

• A is-a relationship
• Represented by: A solid line with a triangular arrow from specialized class to class
• Example: Learner is a role

Composition

• Like aggregation but you can add more constraints.
• An instance of a class can be potentially a component of several classes, but can only be owned by one.
• Represented by: a solid line, with an filled lozange at aggregation end and arror at member end

Multiplicity

• of an association end is the number of possible instances of the class associated with a single instance of the other end.
• Represented on both ends by the following syntax

More

• There is more (sorry)...

Examples[edit | edit source]

IMS Learning Design[edit | edit source]

Here is the official UML Diagram that summarizes the IMS Learning Design educational modeling language:

Here is an annotated version. Blue boxes (roughly) give an idea of the relationships involved.

Here is second try. Annotation is in red (blue boxes wouldn't show well enough when I pasted this into a word processor)

References[edit | edit source]

On line tutorials[edit | edit source]

• IMS Learning Design Information Model, Version 1.0 Final Specification, HTML, retrieved 16:45, 5 June 2007 (MEST).

• Randy Miller, Practical UML: A Hands-On Introduction for Developers, Borland Developer network. (Short and excellent general UML tutorial).

• Donald Bell, UML basics: An introduction to the Unified Modeling Language, IBM Developper Works / Rational Rose. (IBM has a lot of UML and use case tutorials, needs some searching skills)

Books[edit | edit source]

• Fowler Martin (1993). UML Distilled: A Brief Guide to the Standard Object Modeling Language, Third Edition. Addison-Wesley Professional. ISBN 0321193687 (good for quick reference and good enough if you just want to understand how to read UML diagrams).

• Pilone, Dan and Neil Pitman (2005). UML 2.0 in a Nutshell, O'Reilly Media, ISBN 0596007957 (this is the best book Daniel K. Schneider bought, better than the first edition).