The enhanced entity–relationship (EER) model (or extended entity–relationship model) in computer science is a high-level or
conceptual data model incorporating extensions to the original
entity–relationship (ER) model, used in the design of
database
In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...
s.
It was developed to reflect more precisely the properties and constraints that are found in more complex databases, such as in engineering design and manufacturing (
CAD/
CAM
Cam or CAM may refer to:
Science and technology
* Cam (mechanism), a mechanical linkage which translates motion
* Camshaft, a shaft with a cam
* Camera or webcam, a device that records images or video
In computing
* Computer-aided manufacturin ...
),
telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
, complex
software systems and
geographic information systems (GIS).
Mechanics
The EER model includes all of the concepts introduced by the ER model. Additionally it includes the concepts of a
subclass and
superclass (
Is-a), along with the concepts of
specialization and
generalization
A generalization is a form of abstraction whereby common properties of specific instances are formulated as general concepts or claims. Generalizations posit the existence of a domain or set of elements, as well as one or more common characteri ...
. Furthermore, it introduces the concept of a
union type or category, which represents a collection of objects that is the union of objects of different
entity
An entity is something that Existence, exists as itself. It does not need to be of material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is Lif ...
types. The EER model also includes EER diagrams that are conceptual models that accurately represent the requirements of complex databases.
Subclass and superclass
Entity type Y is a subtype (subclass) of an entity type X if and only if every Y is necessarily an X. A subclass entity inherits all
attributes and
relationships of its superclass entity. This property is called the attribute and relationship inheritance. A subclass entity may have its specific attributes and relationships (together with all the attributes and relationships it inherits from the superclass). A common superclass example is a Vehicle superclass along with the subclasses of Car and Truck. There are a number of common attributes between a car and a truck, which would be part of the superclass, while the attributes specific to a car or a truck (such as max payload, truck type...) would make up two subclasses.
Tools
*The
MySQL Workbench offers creating, editing and exporting EER Models. Exporting to PNG and PDF allows easy sharing for presentations.
*
Skipper allows users to create, import and export from
object–relational mapping (ORM) schema definitions to editable EER models.
*SAP
PowerDesignerSAP PowerDesigner
/ref> is a complex tool for modelling and transforming different models.
See also
*Object–relational database
An object–relational database (ORD), or object–relational database management system (ORDBMS), is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inherit ...
* Slowly changing dimension
* Structured type
References
Further reading
Textbooks discussing EER and implementation using purely relational databases:
*
*
*
Booklet discussing EER and implementation using object-oriented and object–relational databases:
*
Textbook discussing implementation in relational and object–relational databases:
*
Shorter survey articles:
*
*
External links
- Slides for chapter 8 from Fundamentals of Database Systems by Elmasri and Navathe (Pearson, 2011)
- Lecture notes from the University of Toronto
- The ER Conference
Data modeling diagrams
Data modeling languages
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