What is RDBMS?
Relational Data Base Management Systems (RDBMS) are database
management systems that maintain data records and indices in tables.
Relationships may be created and maintained across and among the data and tables.
In a relational database, relationships between data items are expressed by
means of tables. Inter-dependencies among these tables are expressed by data
values rather than by pointers. This allows a high degree of data independence.
An RDBMS has the capability to recombine the data items from different files,
providing powerful tools for data usage.
What are the properties of the Relational tables?
Relational tables have
six properties:
- Values are atomic.
- Column values are of the same kind.
- Each row is unique.
- The sequence of columns is insignificant.
- The sequence of rows is insignificant.
- Each column must have a unique name.
What is Normalization?
Database normalization
is a data design and organization process applied to data structures based on
rules that help building relational databases. In relational database design, the process of organizing
data to minimize redundancy is called normalization. Normalization usually involves dividing a database into two or more
tables and defining relationships between
the tables. The objective is to isolate data so that
additions, deletions, and modifications of a field can be made in just one
table and then propagated through the rest of the database via the defined
relationships.
What are different normalization forms?
1NF: Eliminate Repeating Groups
Make a separate table
for each set of related attributes, and give each table a primary key. Each
field contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
If an attribute
depends on only part of a multi-valued key, remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
If attributes do not contribute to a description of the key,
remove them to a separate table. All attributes must be directly dependent on the primary key. (Read More Here)
BCNF: Boyce-Codd Normal Form
If there are
non-trivial dependencies between candidate key attributes, separate them out
into distinct tables.
4NF: Isolate Independent Multiple Relationships
No table may contain
two or more 1:n or n:m relationships that are not directly related.
5NF: Isolate Semantically Related Multiple Relationships
There may be practical
constrains on information that justify separating logically related many-to-many relationships.
ONF: Optimal Normal Form
A model limited to
only simple (elemental) facts, as expressed in Object Role Model notation.
DKNF: Domain-Key Normal Form
A model free from all modification anomalies is said to be in
DKNF.
Remember, these
normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the
criteria of a 2NF and 1NF database.
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