Glossary

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# 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).