Database Administrators:
Database Administrator or DBA is the one who manages the complete database management system. DBA takes care of the security of the DBMS, managing the license keys, managing user accounts and access etc.
Application Programmers or software Developers:
This user group is involved in developing and designing the parts of DBMS.
End User:
All modern applications, web or mobile, store user data. Applications are programmed in such a way that they collect user data and store the data on DBMS systems running on their server. End users are the one who store, retrieve, update and delete data.
Database designers:
Database designers are responsible for identifying the data to be stored in the database for choosing appropriate structures to represent and store the data.

Object model stores the data in the form of objects, attributes and methods, classes and inheritance. This model handles more complex applications, such as Geographic information System (GIS),sdentific experiments, engineering design and manufacturing. It is used in file Management System. It represents real world objects, attributes and behaviors. It provides a clear modular structure. It is easy to maintain and modify the existing code.

An example of the Object model is Shape, Circle, Rectangle and Triangle are all objects in this model
(i) Circle has the attribute radius.
(ii) Rectangle has the attributes length and breadth.
(iii) Triangle has the attributes base and height.
(iv) The objects Circle, Rectangle and. Triangle inherit from the object Shape

(i) Cross product is a way of combining two relations. The resulting relation contains, both relations being combined.
(ii) A x B means A times B, where the relation A and B have different attributes.
(iii) This type of operation is helpful to merge columns from two relations

Database Administrator or DBA is the one who manages the complete database management system. DBA takes care of the security of the DBMS, managing the license keys, managing user accounts and access etc.

Select	Project
1. Symbol - σ	1. Symbol - π
2. Selecting a subset with tuples	2. Contains a vertical subset of relation.
3. Select filters out all tuples that don't satisfy the condition.	3. Projection eliminates all attributes of the input relation except in the projection list.