DATA MODELS:
A data model can be defined as a collection of tools for describing data and the relationship between them.Data models can be classified into the following groups.
Object oriented logical models.
Record based logical models.
Physical data models.
Object oriented logical models:
They are used in describing data at the conceptual and view levels. Some of the widely known models are
Entity Relationship model(ER model): is based on real world perception which consists of collection of basic objects called ‘Entities’ and ‘relationships’ among these objects.
Object oriented model: is based on collection of objects. An object contains instance variables within the object. An object also contains bodies of code that operate on the object, called methods.
Record based logical models:
They are used in describing data at the conceptual and view levels. As the database is structured in fixed-format records of several types, they are called as record based logical models.
Some of the widely known models are:
Relational model: represents data and relationships among data by a collection of tables, each of which has a number of columns with unique names.
Network model: represents data by collection of records and relationships among data are represented by links which are viewed as pointers.
Hierarchical model: represents data by collection of records, which are organized as trees rather than arbitrary graphs and relationships among data are represented by links which are viewed as pointers.
Physical models: They are used in describing data at the lowest level.
