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