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Definitions
- domain:
- A domain D is a set of atomic values that defines the value range of attributes.
Example domain- 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).
Example tupel- 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.
Example attribute- 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}.
Example relation scheme- 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}.
Example relation- 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.
Relational scheme termsThe relational scheme of an object (entity) can be represented as a table (relation). In this example the entity are grades. This entity is described with the attributes name, subject and the grade. The domain (or value range) for the attributes name and subjects are all lower- and upper-case characters of the alphabet, the domain for the grades are real numbers from 1 to 6. The structure of this entity without any content is called a relational scheme. Any value that is entered has to be within the defined value range or domain. A row in the table is also called a tuple.
There is a small mistake in the above table. Do you find it?
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