Database: Terms

Useful database terms. Most aren't defined here, but you should know these.

Common DBMSs

Access A popular desktop DBMS by Microsoft.
DB2 A major DBMS from IBM.
MySQL A popular, open-source, RDBMS.
Oracle Perhaps the most extensive (and expensive) (OR)DBMS.
PostgreSQL A popular, open-source, ORDBMS.
SQL Server A RDBMS by Microsoft for servers.

Types of DBMSs

DBMS DataBase Management System
hierarchical DBMS
network DBMS
ODBMS Object-Oriented DBMS (also OODBMS).
OODBMS Object-Oriented DBMS (also ODBMS).
ORDBMS Object-Relational DBMS. A hybrid of the two technologies.
RDBMS Relational DBMS. This is the principle type of DBMS in use today.

Modeling, Diagramming, and Notation

crow's foot notation A system of symbols for indicating multiplicity in relational diagrams.
ERD Entity Relation Diagram.
cardinality Same as multiplicity.
connectivity Same as cardinality or multiplicity. A few authors distinguish between these terms, but many don't.
many-to-many Many-to-many relationships can not be directly represented in a relational database, but are replaced by a bridging table.
multiplicity Same as cardinality.
one-to-many The most common type of relation where many foreign key values can reference a primary key.
one-to-one For each primary key there is at most one corresponding foreign key in a referencing table. Commonly used to implement subset relationships or lookup tables.
participation optional or mandatory.
recursive A relationship between a table and itself. Same as self-referential. Commonly used for a part-of relationship or a tree hierarchy.
relational diagram Same as relational schema.
relational schema Same as relational diagram.


attribute Same as column.
bridge table A table needed to implement a M:N relationship between two other tables in a RDBMS. Typically has a composite key using the primary keys of the two other tables.
calculated attribute Same as derived attribute
composite key A key composed of more than one field.
data type Same as domain.
derived attribute Same as calculated attribute
domain The possible values that an attribute may have, eg, INTEGER. Same as data type.
entity Entity has two interpretations. It can mean a record or a table. It has the table meaning in Entity Relation Diagram and bridge entity.
file Same as table.
foreign key A field which links to the primary key.
index A file used internally by the database to speed access to records. An index is usually generated automatically for primary and foreign keys. A user may request other fields that are searched to be indexed.
key A value which is used to link two or more tables.
NULL Value often used to indicate optional, missing, or unknown value.
primary key The unique value which distinguishes every record.
record Same as row, tuple.
row Same as record, tuple.
table Same as file.
tuple Same as record, row.

Searching, Joining, Manipulating, etc

Cartesian product Same as cross product.
cross product Table formed by joining all possible combinations of the rows of two other tables. This is the basis for most joins (default or inner join). Same as Cartesian product.
DDL Data Definition Language - a language used to define tables, etc. SQL is an example of a DDL.
DML Data Manipulation Language - a language used to access a database. SQL is an example of a DML.
join To combine two or more tables.
query A search of a database. In SQL the SELECT command is used for queries.
SQL Structured Query Language. Pronounced either ess-queue-ell or sequel


DBA DataBase Administrator
data dictionary The metadata about a database. This is, of course, kept in a database, often in the system catalog.
metadata Data about a database, eg the names of the tables and attributes, the attribute domains, etc. This information is typically in the data dictionary.
referential integrity For every foreign key value there must be a corresponding primary key value.
system catalog Metadata database which has information about all databases in DBMS.