4.7.5 Develop UML class diagram for your UML model

From Geostandards

Exercise: Develop a first cut UML class diagram for your domain model. Use Enterpise Architect as the modeling environment. 

The previous exercises have provided a general understanding of the scope, requirements and all ready existing harmonization efforts. In this exercise you will make a UML class diagram that gives a first impression how the specific domain is structured in geographic features, that are characterized by attributes, that are constrained by datatypes and codelists.

Step 1) Do a quick brainstorm on classes that are potentially relevant for your specific domain

Step 2) Assign candidate classes. Analyze the result of step 1). Basic questions are:

• Which elements are synonymous?
• Which elements are more like objects?
• Which elements can be grouped in classes?
• Which elements are usable classes?

For the class question. One should all ways evaluate if the potential class provides independent objects that are relevant to the domain you are modeling. Do objects (instances) of the class really have an independent information content? Since we are modeling in the geo-information domain the boundary of objects is an important aspect of information content. Which objects do we want to distinguish in the simulated reality? Do these objects have different characteristics (attributes)?

• Is there a grouping of classes? Which classes can be grouped into more general classes. Assign super classes and sub classes.

Step 4) Use Enterprise Architect to design a general UML diagram from the candidate classes that are chosen in step 3. Try to incorporate several super classes (GeoObject is a suggestion) and specialize subclasses.

Step 5) Assign basic definitions for the defined classes.

Step 6) Evaluate if there are relations (associations, aggregations, compositions) between classes (instances of classes). For instance between Building and Owner, Municipality and Province etc. Name the specific roles the classes can have in these associations.

Step 7) Specify for each class the attributes that belong to the class. When identifying candidate attributes try to evaluate if this information really is part of the ‘responsibility’ of the instances. Should instances be able to provide this kind of information? Or are there other classes that are more appropriate?

Step 8) For the attributes assign datatypes or enumerations. Examples are CharacterString, Integer, GM_Surface, Date, etc.

Step 9) Assign multiplicity to attributes and roles. Which attributes are mandatory (1), which are optional (0..). Which have a multiple cardinality. (x..n)?

Step 10) Evaluate if there are any constraints on model elements. Evaluate if there are dependencies between attributes or attribute values. Dependencies between roles of classes. Formulate the dependencies. Assign constraints with notes to the model elements.

Step 11) You have constructed a UML class diagram for the specified domain. Explain the class diagram to a fellow course participant. Explain the scope and modeling decisions. Discuss issues and discuss open issues in particular. Try to get useful feedback that can be use for improving the class diagram.
Remark:
In the practice of modeling a next step would be to present the results to the stakeholders. Feedback from that session will then lead to subsequent re-modeling. A process of several iterations will generally lead to a consensus on the class model.

Step 12) End. Congratulations. You have constructed a class diagram and presented it to your fellow course participant. You can use the received feedback and your improved vision on the domain to improve and or augment the class diagram. But for now this exercise has ended and hopefully provided you with a valuable experience designing an UML class diagram.

Example: Below a UML class diagram of the Land use model is presented that might be the result of a similar exercise.

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