| Term | Definition |
|---|
| Entity Type | A collection of persons, places, events, or things of interest represented by a rectangle in an ERD. |
| Attribute | A property of an entity type or relationship. Each attribute has a data type that defines the kind of values and permissible operations on the attribute. |
| Relationship | A named association among entity types. Represents a two-way or bidirectional association among entities. Most involve two distinct entity types. |
| Cardinality | A constraint on the number of entities that participate in a relationship. In an ERD, the minimum and maximums are specified for both directions of a relationship. |
| Existence Dependency | An entity that cannot exist unless another related entity exists. A mandatory relationship creates an existence dependency. |
| Mandatory Relationship | Represented by a cardinality of one or more. |
| Optional Relationship | Represented by a minimum cardinality of zero. |
| Single Valued/Functional | Represented by a maximum cardinality of one. |
| 1-1 | Maximum Cardinality equals one in both directions. |
| Weak Entity | An entity type that borrows all or part of its primary key from another entity type. Identifying relationships indicate the entity types that supply components of the borrowed primary key. |
| Identification Dependency | Occures because some entities are closely associated with other entities. |
| Self-Referencing Relationship | A relationship involving the same entity type. Self referencing relationships represent associations among members of the same set. |
| Associative Entity Type | A weak entity that depends on two or more entity types for its primary key. An associative entity type with more than two identifying relationships is known as an M-way associative type. |
| Ternary Relationship | An M-way relationship involving three entity types. |
| Relationship Equivalence | A M-N relationship can be replaced by an associative entity type and two identifying 1-M relationships. In most cases the choice between a M-N relationship and the associative entity type is personal preference. |
| Generalization Hierarchy | A collection of entity types arranged in a hierarchical structure to show similarity in attributes. Each subtype or child entity type contains a subset of entities of its supertype or parent entity type. |
| Inheritance | A data modeling feature taht supports sharing of attributes between a supertype and a subtype. Subtypes inherit attributes from their supertype. |
| Primary Key Rule | All entity types have a primary key (direct, borrowed, or inherited). |
| Naming Rule | All entity types, relationships, and attributes are named. |
| Cardinality Rule | Cardinality is given for both entity types in a relationship. |
| Entity Participation Rule | All entity types except those in a generalization hierarchy participate in at least one relationship. |
| Generalization Hierarchy Participation Rule | Each generalization hierarchy participates in at least one relationship with an entity type not in the generalization hierarchy. |
| Entity Name Rule | Entity type names are unique. |
| Attribute Name Rule | Attribute names are unique within the entity types and relationships. |
| Inherited Attribute Name Rule | Attribute names in a subtype do not match inherited (direct or indirect) attribute names. |
| Relationship/Entity Type Connection Rule | All relationships connect two entity types (not necessarily distinct). |
| Relationship/Relationship Connection Rule | Relationships are not connected to other relationships. |
| Weak Entity Rule | Weak entities have at least one identifying relationship. |
| Identifying Relationship Rule | For eac identifying relationship, at least one participating entity type must be weak. |
| Identification Dependency Cardinality Rule | For each identifying relationship, the minimum and maximum cardinality must be 1 in the direction from the child (weak entity) to the parent entity type. |
| Redundant Foreign Key Rule | Redundant foreign keys are not used. |
Combine with other sets
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