Generalization Sets

In SysML, Generalization means Inheritance. A «block» may generalize another «block», or in other words, one «block» may be a superclass of another. We say that a subclass «block» inherits from a superclass «block». SysML allows for multiple generalization (i.e., multiple inheritance) in which one «block» inherits the properties from multiple «block» elements. Conversely, multiple «block» elements may inherit from a single «block». Subclass «block» elements which inherit from a superclass «block» may be organized into groups, called Generalization Sets. Each Generalization Set possesses a Name, a Coverage property, and an Overlap property.

The Coverage property of a Generalization Set is either Complete or Incomplete. In other words, the elements of the Generalization Set represent all possible subclasses (i.e., complete) or only a portion of the possible subclasses (i.e., incomplete). A complete Generalization Set could include all elements of the periodic table and an incomplete Generalization Set could include only the Alkali Metals.

The Overlap property of a Generalization Set is either Disjoint or Overlapping. A Disjoint Generalization Set infers that the elements of the set are mutually exclusive. An Overlapping Generalization Set infers that the elements are not mutually exclusive. An example of a Disjoint Generalization Set is {circle, square}. An example of an Overlapping Generalization Set is {square, rectangle}.

Generalization Set example

Not all tools display the Generalization Set name and value of Coverage and Overlap on the Block Definition Diagram. For those that do, the Generalization Set Name with Coverage and Overlap values are displayed next to the Generalization connector (e.g., Cylinder Type, {Incomplete, Disjoint} or Combustion Engine Type, {Complete, Disjoint}).

Reference:

Friedenthal, S., Moore, A., & Steiner, R. (2012) A Practical Guide to SysML. Waltham, MA: Morgan Kaufmann. pg. 141