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Summary
In a relational model real world objects are represented in tables.
Each table is made out of rows and columns. Each row, also known as tuple or
record, is made out of fields, also known as attributes. Each Attribute stands
for a certain feature of the real world object. An attribute is defined by a
name and its value.
Relations between tuples represent existing relationships between
objects (tables). Furthermore key attributes have to be defined (usually
displayed underlined in a relation). They are necessary for the allocation
(relation) of objects (tables) and allow unique accesses to tables.
Integrity or consistency stands for the quality and reliability of
data of a database system. A database is consistent if the data reflects the
referenced objects correctly. It is inconsistent if there exist ambiguous or
contradictory tuples, relations or tables in the database.
A relation model (scheme, entity) should reflect relationships that
also logically (in the real world) belong together. To avoid anomalies
different types of normalisations help keeping the database consistent.
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