Topic: existence of database entities

topics > computer science > database > Group: database model

database as a model of reality
database entities
entity-relationship database model
facts as relationships between entities
fundamental concepts such as type, attributes, relationships are all the same
object and value equivalence
unique names


One of Kent's themes is the importance of existence in a database model. More accurately, a database model expresses awareness of things through its data structures and identifiers. Typically existence is represented by a logical record with a unique identifier and a collection of single-valued facts. Existence may also be represented syntactically, by a predicate, by membership in a list, or implicitly. There is an ill-defined boundary between the representation of existence and relationships. (cbb 3/98)
Subtopic: existence of entity up

Quote: need database mechanism to announce the existence of an entity [»kentW1_1984]
Quote: the existence of all entities, symbols, relationships should be explicitly asserted [»kentW_1978]
Quote: objects with qualified names should be entities independent of the qualifier [»kentW_1978]

Subtopic: durable, unique up

Quote: durability (preserved under change) and distinguishability are important aspects of identity [»kentW6_1991]
Quote: database entities which exist, will have single-valued facts associated with them
Quote: the extensional set constructor is the ultimate test of identity; cardinality of the set is one [»kentW6_1991]

Subtopic: detect existence up

Quote: define function 'exist' which is turned into a predicate for testing existence [»deapAM2_1984]
Quote: system can detect existence of objects (surrogate, representative, thing) and can interrelate them [»kentW_1978]

Subtopic: list test up

Quote: list test for existence: if symbol on a list, then it exists [»kentW_1978]
Quote: some records correspond one-to-one with entities; the entity exists only if the record exists; referential integrity and primary keys [»kentW1_1985]
Quote: define existence by membership in an existence list for some type [»kentW_1978]
Quote: existence by membership in list of objects referenced by symbols [»kentW_1978]

Subtopic: syntactic test up

Quote: syntactic checks for existence: a symbol is numeric, alphabetic, fixed length [»kentW_1978]
Quote: syntactic test of existence works for numbers, but not for strings, e.g., addresses [»kentW_1978]

Subtopic: existence is subjective up

Quote: a computational system expresses awareness of things (via tokens or references), rather than the existence of things [»kentW6_1991]
Quote: there are no objective criteria for the entities identified by data analysis; boundary between entity and non-entity is highly subjective [»kentW1_1985]
Quote: can't represent a thing by its description; due to its relationships to other things [»kentW_1978]

Subtopic: existence not necessary up

Quote: distinct entities do not need to be distinguished, e.g., several vacant jobs [»kentW_1978]
Quote: lengths, colors etc. can occur in a database without existence being announced

Related Topics up

Topic: database as a model of reality (25 items)
Topic: database entities (12 items)
Topic: entities (20 items)
Topic: entity-relationship database model (22 items)
Topic: facts as relationships between entities (22 items)
Topic: fundamental concepts such as type, attributes, relationships are all the same (37 items)
Topic: object and value equivalence (60 items)
Topic: unique names
(58 items)

Updated barberCB 5/04
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