Database Chapter 4
Composite key
A key that consist of more than one attribute
Attributes
A named column of a relation
Base relation
A named relation corresponding to an entity in the conceptual schema, whose tuples are physically stored in the database
Tuple
A row of a relation
Domain
A set of allowable values for one or more attributes
Candidate key
A super key such that no proper subset is a superkey within the relation
Superkey
An attribute or set of attributes, that uniquely identifies a tuple within a relation
Foreign Key
An attribute, or set of attributes, within one relation that matches the candidate key of some relation
Referential integrity
If a foreign key exists in a relation, either the foreign key value must match a candidate key value of some tuple in its home relation or the foreign key value must be wholly null
Entity Integrity
In a base relation, no attribute of a primary key can be null
Intension
Internal structure of the database
Normalized relations
Relations that have no repeating groups
Null
Represents a value for an attribute that is currently unknown or is not applicable for this tuple
Relational database schema
Set of these with distinct name
Relation
Table with columns and rows
Primary key
The candidate key that is selected to identify tuples uniquely within the relation
Alternate keys
The candidate keys that are not selected to be the primary key
view
The dynamic result of one or more relational operations operating on the base relations to produce another relation
Degree
The number of attributes it contains
Cardinality
The number of tuples it contains
External
The part that can change (view)
Relational Database
a collection of normalized relations with distinct relation names
General constraints
additional rules specified by the users or database admins of a database that define or constrain some aspect of the enterprise
Relation schema
named relation defined by a set of attribute and domain name pairs
