Just as the tool map schema supports simple class models, class inheritance models, and class/interface models, there are three types of mapping that closely correspond to these models:
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Direct mapping
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Mapping including generalized classes in map
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Mapping including realized classes in map
The type of mapping that is used has no impact on the cardinalities of mapping. All three types of mapping can be used in one-to-one, one-to-many, many-to-one, and many-to-many mapping cases.
Direct Mapping
The simplest mapping type is direct mapping. In direct mapping, only map properties for the map class being mapped are used. Any generalized or realized map classes for the map class are not used in the mapping.
For example, if direct mapping is used for map class E, shown in the following diagram,
then only property PE will be mappable. Properties on generalized map classes A, B,
C, and D will not be included in the mapping.
Direct mapping is useful in two cases:
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When the model is a simple class model with no inheritance or interfaces
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When the properties for a generalized map class or a map interface always map the same regardless of the specialized class (for generalized classes) or the realizing map class (for map interfaces). For example in the previous UML diagram, if property PD on map class D always maps to PropD on interface ISmartPlantC, then the mapping for map class D can be defined to be direct.
Mapping Including Generalized Map Classes
When the tool map schema is used to represent a class inheritance model, the mapping type is usually mapping including generalized map classes. With this mapping type, the definition of the map property mapping for a map class will include properties from direct and indirect generalizations of the map class. For the previous example, the mapping of map class E includes the map properties from generalized map classes A, B, C, and D as shown in the following diagram:
A characteristic of mapping using generalized map classes is that a property on a generalized class might map differently depending on the specialized class being mapped. For example, map property PD on map class D maps to property PropD for specialized map class E in the previous diagram, but the same property for specialized map class F maps to property PF in the following diagram.
Mapping Using Realized Map Classes
Just as mapping using generalized map classes is intended for use with class inheritance models, mapping using realized map classes is intended for use with class/interface models. With mapping using realized map classes, mapping for a map class includes mapping the map properties for each map interface realized by that map class. For example, if map class E realizes map interfaces IA, IB, IC, ID, and IE, then mapping E will include mapping the properties for IA, IB, IC, ID, and IE as shown below.
Like mapping using generalized map classes, mapping involving realized map classes can result in a map property for a map interface being mapped differently depending on the realizing map class.