| 
|
Topic: database entities
topics >
computer science >
database >
database as a model of reality
Topic:
entities
Topic:
entity-relationship database model
Topic:
existence of database entities
Topic:
fact-based analysis for database design
Topic:
hypertext nodes
Topic:
objects as a set of attributes
Summary
A database entity is a node or record that contains attributes and links to other nodes. Kent proposes pseudo-records which include actual entities instead of links.In Jackson System Design, an entity is defined by the processes it participates in.
An entity should be distinguished from its name. This is important when a proper name is missing, when an entity has multiple names, or when an entity is renamed. An entity should also be distinguished from its reference. (cbb 4/94)
Subtopic: uniqueness vs. value
Quote: a thing object is a node on a graph; its label may be changed, deleted, or duplicated [»kentW_1978] Quote: information objects have an identity independent of their structure or attributes [»borgA10_1986] Quote: attributes of an object are annotations to the nodes of the directed graph representing the system [»handP_1981] Quote: DELTA is made of objects represented by entities; entities are the nodes of a directed graph [»handP_1981]
Subtopic: entity as data records
Quote: uniqueness of an object depends only on its external relations; exactly the opposite of a value [»maclBJ12_1982] Quote: in conceptual modeling, an object is not the same as a unique name; allows missing proper names, modified names, and multiple names [»borgA1_1985] Quote: the data model of a library may use separate objects for two different books, or two copies of the same book, or a single copy at different times [»holtAW_1979]
Subtopic: entity as actions
Quote: most data models use data records for real entities and assume that other things are not real entities [»kentW1_1985] Quote: database entities which exist, will have single-valued facts associated with them Quote: in a pseudo-record, actual entities (e.g., employees) sit in fields of the record [»kentW1_1984]
Quote: JSD defines an entity in terms of its actions and relevant events; e.g., a BOOK is ACQUIRED, CLASSIFIED, LENT, etc. [»cameJR2_1986] Quote: JSD defines 'entity' as a process that describes constraints on the orderings of events
[»cameJR2_1986]
Topic: database as a model of reality (25 items)
Topic: entities (20 items)
Topic: entity-relationship database model (22 items)
Topic: existence of database entities (19 items)
Topic: fact-based analysis for database design (15 items)
Topic: hypertext nodes (19 items)
Topic: objects as a set of attributes
(39 items)