What is database and Overview of DBMS Structure

Database Definition: 

Database means it is an organized collection of interrelated data (or) structured data stored in place within the hard disk is called as database.

Structured data means, the data in the form of tables called as structured. And the same way RDMS databases have the interrelation or we can say "link" between the database objects(example: tables) So we called it as interrelated.

Every database mainly consists of two types of structures.

1. Physical structure : A structure which is visible in OS(operating system) is called physical structure.

                                    Example : Physical folders of software in your computer

2.Logical structure : A structure which is not visible in OS is called as Logical structure.

                                 Logical structure contains tables, views, sequences, procedures...etc.

In Real-time, Logical structure will be handled by database developers and database Admin's.

DBMS Structure:

•  American national standard institute(ANSI) has established three level architecture for DBMS

• Main objective of the DBMS architecture is to separate the user view of the database from the way physically it stored.

• This architecture also called as 3 level architecture or ANSI/SPARC architecture.

This architecture contains 3 levels. Those are

1. External Level

2.Conceptual level.

3. Internal level.

1.External level:  External level stores the Views and synonyms. So the external level provides the security for the data within the conceptual level that means only few users are allowed to access the specific data of the conceptual level data.

 Here the database admin creates the views to restrict the data . So all users can't  access the full data. So this will add the security to our data.

I will explain about the database objects(views and synonyms) In-Detailed in my future posts.

2.Conceptual Level:  Conceptual level defines what type of data can be stored in database by specifying data type and also conceptual level defines what type of can't be stored in database by specifying the constrains(example : primary Key). Conceptual level stores the tables.

3. Internal Level: Internal level describes, how the the data will be stored in the database and also covers the data structures and files.

Example : Index and clusters.

DBMS architecture provide the data independence. It means the upper levels won't effect by changing the lower level objects. We can divide this in two ways

1.Logical data independence: Changes in the conceptual level don't require changes to the external level.

Example: adding a new entity in conceptual level should not effect external level.

2.Physical data independence.:  Same way changes in the internal level doesn't require changes to the conceptual level.

I will explain in-detailed about the constrains, index, synonyms and others in my future posts.

Simple flow diagram:

EXTERNAL LEVEL <------------> CONCEPTUAL LEVEL <--------->INTERNAL LEVEL <--> DB