Principles Of Conceptual Database Design Flashcards
(29 cards)
Model
A representation of reality that retains only selected details.
Map
To associate elements in one sphere with elements in an other sphere.
Object-Oriented-Model
A model representing real world entities as objects rather than records.
Semantic model
A model that captures the meanings of real world entities and relationships.
Object Set
A set of things of the same kind.
Object Instance
A particular member of an object set.
Lexical Object Set
An object set consisting of instances that can be printed.
Abstract object set
An object set consisting of instances that cannot be printed.
Surrogate key
A unique computer system identifier for an abstract object instance. it has no meaning outside the computer system.
Specialization
An object set is a subset of another object set.
Generalization
An object set that is a superset of(or contains) another object set.
Relationship
A linking between instances of two object sets.
Aggregate Object Set
A relationship viewed as an object set.
Cardinality
The maximum number of instances of one object set related to a single instance of the other object set.
A Functional Relationship
A relationship having a maximum cardinality o one in at least one direction.
One to One
Relationship cardinalities of one in both directions.
One to Many
Relationship cardinalities of one in one direction and many in the other.
Many to Many
Relationship cardinalities of many in both directions.
Attribute
Functional relationship from an object set to another set.
Null attribute value
An attribute value that does not exist for a specific object instance.
Key
A value that can always be used to uniquely identify an object instance.
External Key
A set of lexical attributes whose values always identify a single object instance.
Identifier
An external key
Inherit
The property of a specialization set that causes it to have all the attributes of its generalization set.
