Introduction


A database system is basically a computer based record keeping system. The collection of data, usually referred to as the data base, contains information about one to particular enterprise.it maintains any information that may be necessary to the decision-making processes involved in the management of that organization.

A database may also defined as a collection of table where  table is a collection of rows and columns or interrelated data stored together to serve multiple applications.


Schema:  The overall design or entire skeleton of a database is called as schema, of a database and schema explain design concept of database.   


Tuple: The rows of tables (relations) are generally  referred to a as tuples(usually pronounced to the Ryhme with "couples").


Attributes: The columns of tables (relations) are generally  referred to a as attributes.




Advantages of DBMS:

  • Data Independence.
  • Efficient Data Access.
  • Data Integrity and security.
  • Data administration.
  • Concurrent access and Crash recovery.
  • Reduced Application Development Time.


The following are the main disadvantages of file processing system in DBMS:

  • Data redundancy and inconsistency.
  • Difficult in accessing data.
  • Data isolation.
  • Data integrity.
  • Concurrent access is not possible.
  • Security Problems.


Difference Between File System and DBMS:



A Keys:


From a database prospective the difference among them must be expressed in terms of their attributes. Keys come here for rescue.

Some keys are following : 

Super Key

Group of keys which is used to identify a particular record among groups of records.


Primary Key:

A primary key is a set of one or more attributes that can uniquely identify tuples within the relation.

A Primary key also can be defined as a key which contains always a unique volume and never contains null value.

i.e  primary key= unique + not null. 


Candidate Key:

All attributes combinations inside a relation that can be serve as primary key are candidate keys as they are candidate for the primary key position.

candidate key is also defined as the minimal super key used to identify a record is called as candidate key. 


Alternate Key:

A candidate key that is not the primary key is called an alternate key.


Foreign Key:

A non-key attribute, whose values are derived from the primary key of some other table, is known as foreign key.


Constraints:

Constraints can be defined as the different conditions which are implement on our database to secure it form 

data constraints are also applied to protect invalid task and also from invalid user.


These are following types of Constraints:


1. Primary key constraints: It means a field when declare us primary. it will not take duplicate value.


2. Not-null constraints: when a field is declare as not-null  it means the field cannot be left blank.


3. Referential integrity constraints:  A referential integrity constraints state that if you want to enter                                                                  any value in child table then its corresponding empty must be made in parent table firstly.

 

Codd's Rule:

Dr. EF codd was the scientist who gave 12 rules for a relational database also called as golden rules of codd. He gave this rule and state that for an effective database. 

The database must satisfies at least seven(T) rules so that database can be easily maintained. 


1. Physical data independence:

    According to this rule if any changes (are made) in the physical schema must not affected data                access from a database.

2. Logical data independence:

    According to this rule if any changes (are made) in the logical schema of database and still we are          able to access data from database, then it states database is full-filling logical independency.

3. Null Value specification:

   According to this rule null value in the database effectively handled.

4. High level of insert, update and delete:

   According to this rule a database must support insertion, updation and deletion property in database.

5. Gauranted access from database:

    According to this rule changes made in database should not affect data of the table and hence we can      easily retrieve data from database.

6. Rule of information:

     As we know that data in a database or table is stored inform of records for an effective database we         must have complete description of the table.  

7. Active online catalog:

    A catalog means index representing the detailed information of each and every record, whenever            any operation(insert, update, delete) is performed on database the value must updated at the same          time so that date can be easily and quickly access from database.

8. Comprehensive data sub language:

   It is not possible to explain the complete language of quarry hence additional language must be               defined know as sub languages.

9. View updating rule:

    A view reflects parts of a database. a table must can have more then one view only these view will        be acceptable which can be updateable with the database.    

10: Integrity independence:

    A database must be independence in search a way that any changes in any mode at any state will not      affect records of the database  

11. Distributed independence:

    for an effective relational database it must be or can be distributed among several uses-however it is      distributed to any number of uses it must be location independent and size independent that is a              database can be easily access able to any number of user through network.

12. Non-subversion

   A database can not be subversion means if any changes have  been made in database then it should be gives a new name.