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 stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases s ...
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
Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...
),
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
, 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
In knowledge representation, object-oriented programming and design (see object-oriented program architecture), is-a (is_a or is a) is a subsumption relationship between abstractions (e.g. types, classes), wherein one class ''A'' is a subclass ...
), along with the concepts of
specialization
Specialization or Specialized may refer to:
Academia
* Academic specialization, may be a course of study or major at an academic institution or may refer to the field in which a specialist practices
* Specialty (medicine), a branch of medical ...
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 characte ...
. Furthermore, it introduces the concept of a
union
Union commonly refers to:
* Trade union, an organization of workers
* Union (set theory), in mathematics, a fundamental operation on sets
Union may also refer to:
Arts and entertainment
Music
* Union (band), an American rock group
** ''Un ...
type or category, which is used to represent a collection of objects that is the union of objects of different
entity
An entity is something that exists as itself, as a subject or as an object, actually or potentially, concretely or abstractly, physically or not. It need not be of material existence. In particular, abstractions and legal fictions are usually ...
types. 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
attribute
Attribute may refer to:
* Attribute (philosophy), an extrinsic property of an object
* Attribute (research), a characteristic of an object
* Grammatical modifier, in natural languages
* Attribute (computing), a specification that defines a prope ...
s and
relationships of its superclass entity. This property is called the attribute and relationship inheritance. A subclass entity may have its own 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 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
*Slowly changing dimension
A slowly changing dimension (SCD) in data management and data warehousing is a dimension which contains relatively static data which can change slowly but unpredictably, rather than according to a regular schedule. Some examples of typical slowly ...
* 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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