Chapter 2

record

(1) a group of fields pertaining to the same entity; used in file processing systems (2) in the relational model, a synonym for the row and tuple

attribute

(1) a value that represents a characteristic of an entity (2) a column of a relation

well-formed relation

(1) for a relation to be considered well formed, every determinant must be a candidate key (2) any relation that is not well formed should be broken into two or more relations that are well formed

surrogate key

a column with a unique DBMS assigned identifier that has been added to a table to be the primary key

table

a database structure of rows and columns to create cells that hold data values. also known as a relation in a relational database, although strictly only tables that meet specific conditions can be called relations.

normalization process

a four step process for normalizing relations

sequence

a function to define automatically increasing sequences of numbers that can be used as surrogate key numbers

rows

a group of columns in a table. all the columns in a row pertain to the same entity. also known as a tuple or record.

tuple

a group of columns in a table. all the columns in a row pertain to the same entity. also known as a tuple or record.

composite key

a key of a relation that consists of two or more columns

nonunique key

a key that potentially identifies more than one row

columns

a logical group of bytes in a row of a relation or a table. the meaning of a column is the same for every row of the relation

alternate key

a losing candidate key that is still present in the relation

fourth normal form

a relation in BCNF in which every multi-valued dependency is a functional dependency

functional dependency

a relationship between attributes in which one attribute or group of attributes determines the value of another.

relation

a two dimensional array that contains single-value entries and no duplicate rows. the meaning of the columns is the same in every row. the order of the rows and columns is immaterial

candidate key

an attribute or a group of attributes that identifies a unique row in a relation. one of the candidate keys is chosen to be a primary key

null value

an attribute value that has neve been supplied. such values are ambiguous and can mean the value is unknown the value is not appropriate or the value is known to be blank

field

another term for column

file

another word for table in traditional processing

first normal form

any table that fits the definition of a relation

determinant

one or more attributes that functionally determine another attribute or attributes.

key

one or more columns of a relation that is used to identify a row

entity

something of importance to a user that needs to be represented in a database. in the entity-relationship model, entities are restricted to things that can be represented by a single table

identity

specifications that have been set to indicate to SQL server that a surrogate key column exists

identity increment

the amount that is added to each key value to create the next key value

primary key

the candidate key that is chosen as the key that the DBMS will use to uniquely identify each row in a relation

normalization

the process of (or steps for) breaking a table or relation with more than one theme into a set of tables such that each has only one theme

referential integrity constraint

the value of a foreign key must match every value of the primary key (rule)

boyce-codd normal form

well formed relations

synonyms

when two attributes each determine one another