Some databases have more complex requirements than do the more traditional applications. This led to the development of additional semantic data modeling concepts that were incorporated into conceptual data models such as the Entity-Relationship (ER) model.
Various semantic data models have been proposed in the literature. Many of these concepts were also developed independently in related areas of computer science, such as the knowledge representation area of artificial intelligence and the object modeling area in software engineering. This article describes features that have been proposed for semantic data models, and show how the ER model can be enhanced to include these concepts, leading to the enhanced (or extended) ER, or EER, model.
These features include the concepts of subclass and superclass and the related concepts of specialization and generalization that are directly borrowed from the Unified Modeling Language (UML) models. The article also discusses briefly the discipline of knowledge representation and how it is related to semantic data modeling. It proposes an overview and summary of the types of abstract data representation concepts: classification and instantiation, identification, specialization and generalization, and aggregation and association. This explains how EER and UML concepts are related to each of these.
Read the complete article on http://faculty.kfupm.edu.sa/ics/sukairi/ics434/course_resources/2-Advanced%20Data%20Modeling/ch4.pdf