Relational Database Management Systems
SQL
Structured Query Language: a standard data definition and data manipulation language which underpins many RDBMSs
un-normalised form
a representation of the data model consisting of a single entity comprising all attributes. Abbreviated to UNF. Also known as zero normal form
relational model
a type of data model in which data items are grouped into entities which are related, in order to minimise data duplication and achieve data integrity
insertion anomaly
a type of update anomaly where a value for a key field is not available, so preventing data being added to a record
modification anomaly
a type of update anomaly where data duplicated in multiple records may be modified in one record but not in another, leading to data inconsistency
deletion anomaly
a type of update anomaly where the deletion of a record results in the inadvertent deletion of other data
repeating data item
an alternative term for a multi-valued attribute.
non-key attribute
an attribute in an entity which is neither an atomic key nor part of a compound key
answer table
the set of records produced when performing a query
second normal form
the stage of normalisation derived from 1NF in which partial dependencies are removed. Abbreviated to 2NF
third normal form
the stage of normalisation derived from 2NF in which non-key dependencies are removed. Abbreviated to 3NF
zero normal form
An alternative name for un-normalised form (indicating its position as the stage prior to first normal form)
dependent
See dependency
1NF
See first normal form
indirect dependency
See non-key dependency
transitive dependency
See non-key dependency
2NF
See second normal form
3NF
See third normal form
UNF
See un-normalised form
0NF
See zero normal form
first normal form
The stage of normalisation derived from 0NF in which multi-valued attributes are removed. Abbreviated to 1NF
data dictionary
a description (usually in a table) of the properties of each attribute in an entity, appropriate for implementation within any RDBMS
update anomalies
a general term describing problems associated with flat file databases and partially normalised data models. See insertion anomaly, modification anomaly, deletion anomaly
atomic key
a key consisting of only one field
compound key
a key which is made up of a set of fields
surrogate key
a key which is made up purely for the purpose of uniquely identifying records
lookup
in a RDBMS, a means of entering values into a field based on entries in a related table (primarily used to achieve referential integrity for foreign keys)
macro
in a RDBMS, a means of recording a sequence of application operations which can then be re-applied automatically
navigation
in a RDBMS, the means of switching from one view of the data to another by using buttons, macros and scripting
scripting
in a RDBMS, the use of a simplified programming language to automate application tasks, such as performing queries, displaying forms, and generating reports
sort key
in a sorting operation, a field whose values are used to arrange records into order. See primary sort key, secondary sort key
partial dependency
in an entity with a compound key, where a non-key attribute is dependent on only part of the key
candidate key
one of a set of possible keys
RDBMS
relational database management system: database software based on the relational model
data integrity
when data can be guaranteed to be accurate and reliable
data redundancy
when data is unnecessarily duplicated in a database
data consistency
when the same data used in several places corresponds in each occurrence
non-key dependency
where a non-key attribute is dependent primarily on another non-key attribute
referential integrity
where the value of any foreign key in one table is guaranteed to refer to an existing record in the related table
dependency
where the value of one attribute Y can be determined by the value of another attribute X. Y is dependent on X if for a given value of X there is only one value for Y
