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For instance, a person entity can be linked to a car without one of them being considered as weak entity. In entity relationship diagrams (ER diagrams) , a weak entity set is indicated by a bold (or double-lined) rectangle (the entity) connected by a bold (or double-lined) type arrow to a bold (or double-lined) diamond (the relationship).
A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can exist between entities (instances of those entity types). In software engineering , an ER model is commonly formed to represent things a business needs to remember in order to perform business processes .
An associative entity is a term used in relational and entity–relationship theory. A relational database requires the implementation of a base relation (or base table) to resolve many-to-many relationships. A base relation representing this kind of entity is called, informally, an associative table. An associative entity (using Chen notation)
Each instance of the category entity is simultaneously an instance of the generic entity. Non-specific relationships A relationship in which an instance of either entity can be related to any number of instances of the other. View levels Three levels of view are defined in IDEF1X: entity relationship (ER), key-based (KB), and fully attributed (FA).
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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 databases.
In systems analysis, a one-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model). For example, take a car and an owner of the car. The car can only be owned by one owner at a time or not owned at all, and an owner could own zero, one, or multiple cars.