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 spa ...
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 tha ...
, complex
software systems
A software system is a system of intercommunicating components based on software forming part of a computer system (a combination of hardware and software). It "consists of a number of separate programs, configuration files, which are used to s ...
and
geographic information systems
A geographic information system (GIS) is a type of database containing geographic data (that is, descriptions of phenomena for which location is relevant), combined with software tools for managing, analyzing, and visualizing those data. In a ...
(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 subclas ...
), 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 character ...
. 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 r ...
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
attributes and
relationship
Relationship most often refers to:
* Family relations and relatives: consanguinity
* Interpersonal relationship, a strong, deep, or close association or acquaintance between two or more people
* Correlation and dependence, relationships in mathem ...
s 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
MySQL Workbench is a visual database design tool that integrates SQL development, administration, database design, creation and maintenance into a single integrated development environment for the MySQL database system. It is the successor to ...
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
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 inheritan ...
*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 slowl ...
* 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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