(3) The Realational Database Model Flashcards
Determination
The role of a key. In the context of a database table, the statement “A determines B” indicates that knowing the value of attribute A means that the value of attribute B can be looked up.
Primary key (PK)
In the relational model, an identifier composed of one or more attributes that uniquely identifies a row. Also, a key selected as a unique entity identifier.
Composite key
A multiple-attribute key
Key
One or more attributes that determine other attributes.
Predicate logic
Used extensively in mathematics to provide a framework in which an assertion (statement of fact) can be verified as either true or false.
Foreign key (FK)
An attribute or attributes in on e table whose values must match the primary key in another table or whose values must be null.
Dependent
An attribute whose value is determined by another attribute.
Prime attribute
A key attribute; that is, an attribute that is part of a key or is the whole key.
Secondary key
A key send strictly for data retrieval purposes. For example, customers are not likely to know their customer number (primary key), but the combination of last name, first name, middle initial, and telephone number will probably match the appropriate table row.
Super key
An attribute or attributes that uniquely identify each entity in a table.
Unique index
An index in which the index key can have only one associated pointer value (row).
Linking table
In the relational model, a table that implements an M:M relationship.
Domain
In data modeling, the construct used to organize and describe an attribute’s set of possible values.
Null
The absence of an attribute value. Note that this is not a blank.
Functional dependence
Within a relation R, an attribute B is functionally dependent on an attribute A if and only if a given value of attribute A determines exactly one value of attribute B. The relationship “B is dependent on A” is equivalent to “A determines B,” and is written as A B.
