The Unified Modeling Language (UML) defines an Abstraction as a Relationship that relates two Elements or sets of Elements that represent the same concept at different levels of abstraction or from different viewpoints.
Semantically, an Abstraction is a Dependency that relates two NamedElements or sets of NamedElements that represent the same concept at different levels of abstraction or from different viewpoints. The relationship may be defined as a mapping between the suppliers and the clients. Depending on the specific stereotype of Abstraction, the mapping may be formal or informal, and it may be unidirectional or bidirectional. Abstraction has predefined stereotypes (such as Derive, Refine, and Trace) that are defined in UML’s Standard Profile. If an Abstraction has more than one client, the supplier maps into the set of clients as a group. For example, an analysis-level Class might be split into several design-level Classes. The situation is similar if there is more than one supplier.