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== Definition ==

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

{{quotation|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).

{{quotation|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 ==

Class diagrams are made with quite a complex "language".
Here are some elements (I know I have to go over this - [[User:Daniel K. Schneider|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
<table border="1">
<tr><th>Multiplicities</th><th>Explanation 
The notation n . . m indicates n to m instances.
</th></tr>
<tr>
<td>0..1</td>
<td>zero or one instance.</td>
</tr>
<tr>
<td>0..*  or  *</td>
<td>no limit on the number of instances (including none).</td>
</tr>
<tr>
<td>1</td>
<td>exactly one instance</td>
</tr>
<tr>
<td>1..*</td>
<td>at least one instance</td>
</tr>
</table>

; More
* There is more (sorry)...

== Examples ==

=== IMS Learning Design ===

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

[[Image:imsld_infov1p03.gif|frame|none|UML diagram of IMS Learning Design]]

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

[[Image:ims-ld-annotated-uml.png|frame|none|UML diagram of IMS Learning Design annotated with UML relationships]]

Here is second try. Annotation is in red (blue boxes wouldn't show well enough when I pasted this into a word processor)
[[Image:ims-ld-annotated-uml2.png|frame|none|UML diagram of IMS Learning Design annotated with UML relationships]]

== References ==

=== On line tutorials ===

* IMS Learning Design Information Model, Version 1.0 Final Specification, [http://www.imsglobal.org/learningdesign/ldv1p0/imsld_infov1p0.html HTML], retrieved 16:45, 5 June 2007 (MEST).

* Randy Miller, [http://bdn.borland.com/article/0,1410,31863,00.html Practical UML: A Hands-On Introduction for Developers], Borland Developer network. (Short and excellent general UML tutorial).

* Donald Bell, [http://www-128.ibm.com/developerworks/rational/library/769.html 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 ===

* 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 [[User:Daniel K. Schneider|Daniel K. Schneider]] bought, better than the first edition).

[[Category: Educational modeling languages]]
[[Category: Design methodologies]]
[[Category: UML]]

UML class diagram - Revision history

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