Database is a collection of interrelated data.
Database management system is a software which can be used to manage the data by storing it on to the data base and by retrieving it from the data base.
And DBMS is a collection of interrelated data and some set of programs to access the data.
There are 3 types of Database Management Systems.
Relational DataBase Management Systems(RDBMS):
It is a software system, which can be used to represents data in the form of tables. RDBMS will use SQL2 as a Queries language.
Object Oriented DataBase Management Systems(OODBMS):
It is a software system, which can be used to represent the data in the form of objects. This DBMS will use OQL as a Query language.
Object Relational DataBase Management Systems(ORDBMS):
It is a DBMS which will represents
some part of the data in the form of tables and some other part of the
data in the form of objects. This management system will use SQL3 as a
Query Language, it is a combination of SQL2 and OQL.
How a query could be executed when we send a query to Database?
When we send an SQL Query from SQL prompt to the DataBaseEngine, then Database Engine will take the following steps.
Query Tokenization:
This phase will take SQL query as an input and devide into stream of tokens.
Query Parsing:
This phase will take stream of tokens as an input, with them it tried to construct a query tree. If query parser constructs query tree successfully then it was an indication that no grammatical mistakes in the taken SQL query. Otherwise there are some syntactical errors in the taken SQL query.
Query Optimization:
This phase will take query tree as an input and performs number of query optimization mechanisms to reduce execution time and memory utilization.
Query Execution:
This phase will take optimized query as an input and executes that SQL query by using interpreters internally as a result we will get some output on the SQL prompt.
