Entity relationship (ER) Model is a software engineering model that was developed to represent databases.
They were first developed by Peter Chen and published in the paper “The Entity Relationship Model –
Toward a Unified View of Data” in 1976.
Methods representing ER Models
Methods or modeling languages to represent ER Models:
- Chen
- EER
- IDEF1X
- Bachman
- Martin / IE / Crow’s Foot
- Min-Max ISO
- UML
Chen
In Chen’s notation, entities are represented with rectangles, attributes with circles and relationships with diamonds. Primary keys are underlined.
Enhanced Entity-Relationship (EER) Model
The enhanced entity-relationship model (EER) or extended entity-relationship latest update was in 2019.
EER adds the following concepts to ER:
- Superclass and subclass
- Specialization and generalization
- Union
EER Subclass
Types of constraints on the “subclass” relationship:
- Total or Partial
- Overlapped or Disjoint
Total or partial: a sub-classing relationship is total if every super-class instance is associated with a sub-class entity; otherwise partial.
For example, imagine that “job” is a superclass and “specialization” is a subclass. If all employees within the company work in any specialization, it is a total relationship; if some employees do not have specialization and remain with just a superclass instance, it is a partial relationship.
Overlapped or Disjoint: If an entity from a super-set can be related to multiple sub-class sets at the same time, then it is overlapped sub-classing, otherwise disjoint.
For example, if an employee can have just a single specialization, it is disjoint. If an employee can have different specializations at the same time, it is overlapped.
Métrica v4’s EER
Métrica v4 is methodology developed and used in the public sector of Spain.
This methodology includes an EER (in Spanish modelo entidad-relación or modelo E/R) that adds slight variations to the model of the same name.
You can find more info about Métrica v4 EER on this external link.
Crow’s Foot
As of 2023, Crow’s Foot diagrams can be used in diagrams.net by going to Software > Entity Relationship Diagram.
They are very close to relational databases design, indicating tables with their primary and foreign keys.
UML
UML Class Diagram
UML Class diagrams can be used to represent database entities and their relationship.
UML Data Profile Model
The Data Model Profile is a UML extension to support the modelling of relational databases in UML.
Relationships within an E/R Model
E/R model relationship grades:
- Grade 1, reflexive or recursive
- Grade 2
- Grade 3
- Grade n
- Double
Grade 1, reflexive or recursive involves a single entity.
Grade 2 involves 2 entities.
Grade 3 involves 3 entities.
Grade n involves n entities.
Double involves two different relationships between 2 entities.
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External References
- SPARX Systems; “Database Modeling in UML“; SPARX Systems
- E/R Model Relationships