Database Systems - Chapter 3

Primary key

Attribute or combination of attributes that uniquely identifies any given row

determination

State in which knowing the value of one attribute makes it possible to determine the value of another

functional dependence

Value of one or more attributes determines the value of one or more other attributes.

determinat

Attribute whose value determines another

dependent

Attribute whose value is determined by the other attribute

full functional dependence

Entire collection of attributes in the determinant is necessary for the relationship

composite key

Key that is composed of more than one attribute

entity integrity

Condition in which each row in the table has its own unique identity

null

Absence of any data value that could represent: An unknown attribute value , A known, but missing, attribute value , An inapplicable condition

referential integrity

Every reference to an entity instance by another entity instance is valid

secondary key

Key used strictly for data retrieval purposes

foreign key

an attribute or combo of attributes ine one table whose values must either match the primary key in another table or be null

secondary key

an attribute or combo of attribute used strictly for data retrieval purpose

flags

Special codes used to indicate the absence of some value

relvar

variable that holds a relation

closure

Use of relational algebra operators on existing relations produces new relations

natural join

Links tables by selecting only the rows with common values in their common attributes

equijoin

Links tables on the basis of an equality condition that compares specified columns of each table

theta join

Extension of natural join; it allows you to specify the conditions you like; it is denoted by adding a theta subscript after the JOIN symbol

inner join

Only returns matched records from the tables that are being joined

outer join

Matched pairs are retained and unmatched values in the other table are left null

data dictionary

Description of all tables in the database created by the user and designer

system catalog

System data dictionary that describes all objects within the database

homonym

Same name is used to label different attributes

synonym

Different names are used to describe the same attribute

index key

Index’s reference point that leads to data location identified by the key

unique index

Index key can have only one pointer value associated with it