Data Model

Data Model is a collection of concepts that can be used to describe the structure of the database. Structure means data types, relationships, constraints etc. DBMS allows a user to define the data to be stored in terms of a data model. 

1.  High-level data models 

2.  Low-level data models

3. Representational or Implementation data models 

High-level Data Models

Use set of concepts to describe the database, where the descriptions are close to user views. High-level data models are also known as conceptual models. In conceptual data modeling we use concepts like – entity, attributes, relationship etc. 

Low-level Data Models

Give details about how the data is stored in a computers (storage level details).

Representational/Implementation Data Models

This is in between high-level and low-level data models. Here we represent the concepts described in conceptual model using a specific structures like, networks, objects, tables, trees etc. Ex: Relational Model, NW Model, Hierarchical Model, Object Model, Object relational model etc. 

Relational Model

The central data description construct in this model is a relation, which can be thought of as a set of records. 

Schema

Description of data in terms of a data model is called a schema. A relation schema specifies the name of the relation, fields, type etc. 

eg:. Student (sid: string; name: string; age: integer) every row follows the schema of the relation.

The following are some important representational data models (DBMS Specific) 

1. Network Model

Though the basic structure is a record, the relationships are captured using links. The database can be seen as an arbitrary network of records connected by links. Ex.: GE’s Integrated Data store (IDS), in Early 1960s 

2. Hierarchical Model 

The records containing data are organized as a collection of trees. Ex.: IBMs IMS (Information Management System), in late 1960s 

3. Relational Model (early 1970s)

Data & relationships are captured as tables & keys. Ex.: Oracle, IBMs DB2, MySQL, Informix, Sybase, MS Access, Ingress, MySQL etc. The basic storage structure is a record. 

4. Object Data Model

Objects created through object–oriented programs can be stored in database. Ex.: Object Store 

5. Object Relational Model

Objects can be stores in tables. Ex.: Oracle, Informix