Relational model: A formal structure that organizes data into relations (i.e., tables).
Object-oriented model: Object/relational database management systems (ORDBMSs) add new object storage capabilities to the relational systems at the core of modern information systems
hierarchical model: A database model that organizes data in a top-down (inverted tree) structure.
network model: An extension of the hierarchical model. (See hierarchical model.)
The major types of data models in the history of Databases are:
1) Relational Model
Relational Model organizes data into two dimensional arrays known as relations(tables) and each relation consists of rows and columns. Another major characteristic of relational model is that of keys, designated columns in a relation used to order data or establish relations.
2) Object Oriented Model
Object Model aims to reduce the overhead of converting information representation in the database to an application specific representation. Unlike a traditional database, an object model allows for data persistence and storage by storing objects in the databases. The relationships between various objects are inherent in the structure of the objects. This is mainly used for complex data structures such as 2D and 3D graphics which must otherwise be flattened before storage in a relational database.
Evolution of Object Databases
Object oriented databases or object databases incorporate the object data model to define data structures on which database operations such as CRUD can be performed. They store objects rather than data such as integers and strings. The relationship between various data is implicit to the object and manifests as object attributes and methods
Object database management systems extend the object programming language with 1) transparently persistent data, 2) concurrency control, 3) data recovery, 4) associative queries, and 5) other database capabilities.
3) Hierarchical model
Hierarchical model contains data organized into a tree-like structure.
This supports parent-child relationships between data similar to a tree data structure where object types are represented by nodes and their relationships are represented by arcs. This model is restrictive in that it only allows one to many relationship (a parent can have many children but a child can only have one parent)
An example of this is Jump to search IBM's Information Management System (IMS), which is a joint hierarchical database with extensive transaction processing capabilities.
4) Network Model
Network Model is similar to the hierarchical model in representation of data but allows for greater flexibility in data access as it supports many to may relationships.