Database Chapter 4
Relational database
A collection of normalized relations with distinct relation names
Attribute
A named column of a relation
Tuple
A row of a relation
Relational database schema
A set of relation schemas, each with a distinct name
Superkey
An attribute or set of attributes, that uniquely identifies a tuple within a relation
Relation
File
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
Relation
Physically represented as a table (with columns and rows), based on the mathematical concept of a relation
Tuples
Records
Normalized Relation
Relations that have no repeating groups
Primary key
The candidate key that is selected to identify tuples within the relation
View
The dynamic result of one or more relational operations operating on the base relations to produce another relation. Note: It is a virtual relation that does not necessarily exist in the database but can be produced upon request by a particular user, at the time of request.
Cartesian product
The set of all ordered pairs such that the first element is a member of D1 and the second element is a member of D2
Domain
The set of allowable values for one or more attributes
Intension
The structure of a relation, together with a specification of the domains and any other restrictions on possible values
Extension (or State of a Relation)
This is what tuples are called, which changes over time
Composite key
A key that consists of more than one attribute
Base relation
A named relation corresponding to an entity in the conceptual schema, whose tuples are physically stored in the database
Relational schema
A named relation defined by a set of attributes and domain name pairs
Virtual/derived relation
A relation that does not necessarily exist in its own right, but may be dynamically derived from one or more base relations. ---> view
Candidate key
A superkey such that no proper subset is a superkey within the relation
General constraints
Additional rules specified by the users or database administrators or a database that define or constrain some aspect of the enterprise
Foreign key
An attribute or set of attributes within one relation that matches the candidate key of some (possibly the same) relation
Relational keys
Attributes that uniquely identifies each tuple in a relation
Integrity rules
Constraints or restrictions that apply to all instances of the database
Domain constraints
Constraints that form restrictions on the set of values allowed for the attributes of relations
Each __________ has a name and is made up of named _____________ (columns) of data each ________ (row) contains one value per attribute
Each *relation* has a name and is made up of named *attributes* (columns) of data each *tuple* (row) contains one value per attribute
Fields
Fields
The degree of an unary relation/one-tuple, binary, ternary, n-ary?
Has one attribute; two attributes; three attributes; any number of attributes
Entity integrity
In a base relation, no attribute of a primary key can be null
Null
Represents a value for an attribute that is currently unknown or is not applicable for this tuple
Degree
The number of attributes it contains
Cardinality
The number of tuples it contains
