Elements are related to each other in many ways. Each model element essentially has e.g. at least one owner relationship. Most relationships are shown as edges (lines). Relationships express assignments, inheritances, dependencies, flows, compositions etc.
Relationships can be represented in diagrams by edges (lines), neighboring relationships or nesting. Relationships also require information about type, read direction and navigation direction.
Relationships are always shown in columns and rows in tables according to assignment.
As with the directory tree, the owner relationships are shown with dotted lines in the model tree.
Relationships are an important means of communication in modeling languages. They link one or more elements to each other in a relationship. It is also important to set the semantic for relationships.
Non-directional relationships normally express binary associations (connections) which the direction is not set for.
Directional relationships consist of at least one source and one target. Directional relationships are normally shown as an arrow and the arrowhead points to the target.
Important directional relationships include e.g. inheritance (generalization, specialization), realization, dependency, as well as aggregation/composition.
Taken from a strictly object-oriented view, bi-directional relationships must be regarded as two inverse uni-directional relationships otherwise, e.g. the principle of encapsulating the object involved in a relationship won't be upheld.
Entity relationship modeling only accepts bi-directional relationships.
This semantic difference must be taken into consideration when creating and reading models.
Navigation and read direction are independent of one another.
The navigation direction explicitly specifies whether an object can access another object. If no navigation direction is given, access is open. Relationships can be navigated from either one side only or both sides.
Read direction is only used for understanding association names which are selected depending on the reason for modeling.
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