The Data model is specified as a collection of conceptual tools for describing data, data relationships, data semantics and constraints.
There are number of data models:
Hierarchical data model
Represent Data as Tree of records with nesting similar to JSON
developed for IBM IMS (information Management System)
worked well for one to many relationships
Network model
aka CODASYL model
standardized by CODASYL (Conference on Data Systems Languages)
similar to Hierarchical model tree but each record can have multiple parents
need to remember the access path to each record from the root record
manual navigation using cursor was possible but query language was complicated
Relational model
No need to remember access path
Query optimizer automatically figure out the efficient access path
Entity-Relationship model and so on.
Abstraction
Physical Level
It is the lowest level and is managed by DBMS.
This level consists of data storage descriptions and the details of this level are typically hidden from system admins, developers, and users.
Conceptual or Logical level
It is the level on which developers and system admins work and it determines what data is stored in the database and what is the relationship between the data points.
External or View level
It is the level that describes only part of the database and hides the details of the table schema and its physical storage from the users.
The result of a query is an example of View level data abstraction.
A view is a virtual table created by selecting fields from one or more tables present in the database.