

Glossary
- Attribute:
- A column of a table represents an attribute. It can also be described as a
that a domain D has in arelation scheme R.
- Candidate key:
- Each attribute or minimal combination of attributes that uniquely
identifies any tuple in a relation is called a candidate key. Minimal means
that removing an attribute leaves the key without the ability to uniquely
identify any tuple and therefore not being a candidate key anymore.
- domain:
- A domain D is a set of atomic values
that defines the value range of attributes.
- First normal form:
- A relation is in first normal form if every attribute in every
row can contain only one single (atomic) value.
- Foreign key:
- An attribute in a relational scheme R1 is a foreign key if it is
in relationship with a primary key from R2 and if:
- The domain (value range) of the foreign key in R1 is the same
as the domain of the primary key in R2.
- The set of values of the foreign key in R1 is a subset of all
primary key values in R2.
Foreign keys usually are marked dotted
underlined.
- Full functional dependency:
- We talk about full functional
dependency if attribute B is functional dependent on A, if A is a
composite primary key and B is not already functional dependent on parts of
A.
- Functional dependency:
- If A and B are attributes of relation R, B is
functionally dependenton A (denoted A --> B), if
each value of A in R is associated with exactly one value of B in R.
- Identification key:
- If every attribute B of R is functionally dependent of A, than
attribute A is a primary key.
- Primary key:
- The primary key is one chosen key candidate that acts as the
identification key for a relation. Usually this is a short attribute like a
ID-number (identification key) or username. Attributes of the primary are
commonly underlined.
- Relation:
- A relation r
is one instance of the
relation scheme R(A1, A2, ..., An) containing a set of n-tuples r ={t1, t2, ...
, tn}.
- Relational database scheme:
- A relational database scheme is a set
of relation schemes S = {R1, ..., Rn} together with a set of integrity
conditions. A relational database is a relational database scheme together with
a database instance.
- Relation scheme:
- A relation scheme R
(A1, A2, ..., An)
is made up of a relation name R and a list of attributes {A1, A2, ...,
An}.
- Second normal form:
- A relation is in
second normal form if
it is in 1NF and every non key attribute is fully functionally dependent on the
primary key.
- Third normal form:
- A relation is in third normal form if
it is in 2NF and no non key attribute is transitively dependent on the primary
key.
- Transitive dependency:
- If A determines B and B determines C then C is determined by
(dependent on) A. We write A --> B and B --> C but not B -->
A.
- Tupel:
- A tuple t is a list with n values
t = <d1, d2, ..., dn> where each value di is either an
element of the domain Di or
NULL. A tuple is a record in a relation (row in a table).