DBMS – Data Base Management System
RDBMS – Relational Data Base Management System or Relational DBMS
A DBMS has to be persistent, that is it
should be accessible when the program created the data ceases to exist
or even the application that created the data restarted. A DBMS also has
to provide some uniform methods independent of a specific application
for accessing the information that is stored.
RDBMS adds the additional condition that
the system supports a tabular structure for the data, with enforced
relationships between the tables. This excludes the databases that don’t
support a tabular structure or don’t enforce relationships between
tables.
DBMS does not impose any constraints or
security with regard to data manipulation it is user or the programmer
responsibility to ensure the ACID PROPERTY of the database whereas the
RDBMS is more with this regards because RDBMS defines the integrity
constraint for the purpose of holding ACID PROPERTY. RDBMS may be or may
not be Client Server Database System.
Examples :
DBMS – File System, XML
RDBMS – SQL Server, Oracle
Reference : Pinal Dave (http://blog.SQLAuthority.com)
What are the Properties of the Relational Tables?
Relational tables have the following 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 is De-normalization?
De-normalization is the process of
attempting to optimize the performance of a database by adding redundant
data. It is sometimes necessary because current DBMSs implement the
relational model poorly. A true relational DBMS would allow for a fully
normalized database at the logical level, while providing physical
storage of data that is tuned for high performance. De-normalization is a
technique to move from higher to lower normal forms of database
modeling in order to speed up database access.
How is ACID property related to Database?
ACID (an acronym for Atomicity
Consistency Isolation Durability) is a concept that Database
Professionals generally look for while evaluating databases and
application architectures. For a reliable database, all this four
attributes should be achieved.
Atomicity is an all-or-none proposition.
Consistency guarantees that a transaction never leaves your database in a half-finished state.
Isolation keeps transactions separated from each other until they are finished.
What are the 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, then remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
Third Normal Form (3NF) is most preferable normal form in RDBMS. Normalization
is the process of designing a data model to efficiently store data in a
database. The rules of 3NF are mentioned here
- Make a separate table for each set of related attributes, and give each table a primary key.
- If an attribute depends on only part of a multi-valued key, remove it to a separate table
- If attributes do not contribute to a description of the key, remove them to a separate table.
BCNF: Boyce-Codd Normal Form
If there are non-trivial dependencies between candidate key attributes, then 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.
Reference: Pinal Dave (http://blog.SQLAuthority.com)
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