IST366: Lecture 1.

Relational Data Structure

Relation A relation is a table with columns and rows.

Attribute An attribute is a named column of a relation.

Domain A domain is a set of allowable values for one or more attributes.

Tuple A tuple is a row of a relation.

Degree The degree of a relation is the number of attributes it contains.

Cardinality A cardinality of a relation is the number of tuples it contains.

Relational database A collection of normalized relations with distinct relation names.

Alternative terminology for relational model
Formal term Alternative 1 Alternative 2

Realtion Table File

Tuple Row Record

Attribute Column Field

Alternative terminology for relational model
Formal term	Alternative 1	Alternative 2
Realtion	Table	File
Tuple	Row	Record
Attribute	Column	Field

Relation schema A named relation defined by a set of attributes and domain name pairs.
Example: Let A₁, A₂, ..., A_n be attributes with domains D₁, D₂, ..., D_n. Then the set S = {A₁:D₁, A₂:D₂, ..., A_n:D_n} is a relation schema. A relation R defined by the relational schema S is a set of mappings from the attribute names to their corresponding domains. Thus, the relation R is a set on n-tuples:
(A₁:d₁, A₂:d₂, ..., A_n:d_n) such that d_i belongs to D_i

Relation database schema Aset of relation schemas, each with a distinct name.

Properties of a relation:

the relation has a name that is distinct from all other relation names in the relational schema;
each cell of the relation contains exactly one atomic (single) value;
each attribute has a distinct name;
the values of an attribute are all from the same domain;
each tuple is distinct; there are no duplicate tuples;
the order of attributres has no significance;
the order of tuples has no significance, theoretically. (However, in practice, the order may affect the efficiency of accessing tuples.)

Relational Keys

Supekey An attribute, or a set of attributes, that uniquely identifies a tuple within a relation.

Candidate key A superkey such that there is no proper subset is a superkey in the relation.
A candidate key, K, for a relation R has two properties:

uniqueness - in each tuple in R, the values of K uniquely identify that tuple;

irreducibility - no proper subset of K has the uniqueness property.

Primary key The candidate key that is selected to identify tuples uniquely within the relation.

Foreign key An attribute, or set of attributes, within one relation that matches the candidate key of some (possibly the same) relation.

Relational Integrity

Every dat amodel has a set of integrity rules, which ensures that the data is accurate. Since every attribute has an associated domain, there are constraints (called domain constraints) that form restrictions on the set of values allowed for the attributes of relations.

In addition, there are two important integrity rules, which are constraint sor restrictions that apply to all instances of the database. The two principal rules fo the relational model are known as entity integrity and referrential integrity.

Null represents a value for an attribute that is currently unknown or is not appllicable for this tuple.

Entity integrity in a base relation, noattribute of a primary key can be Null.

Referrential 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.

Enterprise constraints Additional rules specified by the users or database administrators of a database.