Topic: entity-relationship database model

topics > computer science > database > Group: database model

relationship information

data-driven design
database as a model of reality
database entities
database keys and indexing
database schema
existence of database entities
flow diagrams and flow charts
fundamental concepts such as type, attributes, relationships are all the same
kinds of relationships between data
object-oriented design
Petri net
uniform data model


Data often represents entities and relationships. This division is the basis for the entity-relationship model. Attribute-value pairs represent entities. Arrows represent one-one and one-many relations. Relationships may themselves have attributes.

While the relational data model has replaced the network and hierarchical models, the entity-relationship model continues to be important. Entity-relationship diagrams provide a helpful overview of data. Universal modeling language (UML) is helpful for object-oriented design.

Is the division real? While entities and relationships have obvious relevance, they are not clearly demarcated. The division depends on perception and anticipated meanings. The relational model ignores the distinction. In the relational model, data is tabular and relationships between tables are ad hoc. (cbb 8/06)

Subtopic: real entities up

Quote: in conceptual modeling, objects correspond one for one with real entities [»borgA1_1985]
Quote: the real world consists of entities and relationships; basis for entity-relationship model [»chenPP3_1976]
Quote: database entities correspond to real entities [»kentW_1978]

Subtopic: model world as relationships between entities up

Quote: in enterprise schema need to select the important relationship sets and the arity of the mappings [»chenPP_1977]
Quote: to describe data, must represent multiple relationships between objects
Quote: uniqueness of an object depends only on its external relations; exactly the opposite of a value [»maclBJ12_1982]

Subtopic: E-R diagram up

Quote: in an entity-relationship diagram use circles for values and arrows for attributes [»chenPP_1977b]
Quote: diagram a logical data base with boxes for records, arrows for relationships, and sub-boxes for aggregate parts [»martJ_1975, OK]
Quote: identify entities and relationships, draw E-R diagram, identify values and attributes, translate into data-structure and records [»chenPP_1977b]
Quote: entity-relationship describes structure but not operators nor integrity constraints [»coddEF_1990]

Subtopic: attributes up

Quote: observed or measured information about an entity or relationship is expressed as a set of attribute-value pairs [»chenPP3_1976]

Subtopic: RM/T up

Quote: RM/T uses characteristic and associative types to define cartesian aggregations, unconditional generalizations, and alternative generalizations [»coddEF12_1979]
Quote: in RM/T, characteristic entity types describe entities of some other type; subordinate role
Quote: in RM/T, associative entity types interrelate entities of other types; superordinate role
Quote: in RM/T, kernel entity types or sub-types are neither characteristic nor associative types
Quote: RM/T inner kernel entity types are not subtypes of any other type; independently defined [»coddEF12_1979]
Quote: RM/T has nonentity associations for relations which are not themselves objects; a single n-ary relation without characteristic entities [»coddEF12_1979]
Quote: entities of a subtype of an entity type are necessarily entities of the parent type

Subtopic: relations vs. entity-relationship up

Quote: one person's entity is another person's relationship while relations represent both in the same way
Quote: relational model treats entities and relations the same; unlike earlier models [»coddEF6_1970]
Quote: foreign keys blur the distinction between entities and relations

Subtopic: limits of diagrams up

Quote: when graphical tools become popular, a new programming paradigm makes them obsolete; e.g., flowcharts and structured programming; UML may indicate a paradigm shift

Related Topics up

Group: relationship information   (5 topics, 69 quotes)

Topic: data-driven design (41 items)
Topic: database as a model of reality (25 items)
Topic: database entities (12 items)
Topic: database keys and indexing (18 items)
Topic: database schema (29 items)
Topic: entities (20 items)
Topic: existence of database entities (19 items)
Topic: flow diagrams and flow charts (21 items)
Topic: fundamental concepts such as type, attributes, relationships are all the same (37 items)
Topic: kinds of relationships between data (16 items)
Topic: object-oriented design (30 items)
Topic: Petri net (44 items)
Topic: uniform data model
(19 items)

Updated barberCB 5/04
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