Sunday, 3 July 2011

Data Models

Data model is a way of storing and retrieving the data. There are three different data models. Data models differ in the way they allow users to view and manipulate relationships between entities. Each has its own way of storing the data. The following are the three different data models:

 Hierarchical
 Network
 Relational

In this model, data is stored in the form of a tree. The data is represented by parent-child relation ship. Each tree contains a single root record and one or more subordinate records. For example, each batch is root and students of the batch will be subordinates.

This model supports only one-to-many relationship between entities.

This was used in IBM’s Information management system, IMS.

Data is stored along with pointers, which specify the relationship between entities. This was used in Honeywell's Integrated Data Store, IDS.

This model is complex. It is difficult to understand both the way data is stored and the way data is manipulated. It is capable of supporting many-to-many relationship between entities, which hierarchical model doesn’t.

This stores data in the form of a table. Table is a collection of rows and columns. We will discuss more about relational model in the next second.

SQL Interview Questions and Answers

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