Data Models


Data Models

Data Model: A set of concepts to describe the structure  of a database and certain constraints that the database should obey

 Many forms of data models
 Makes data abstraction possible
  Hides details of physical data storage from the user

Most commercial database systems are based on relational data  model

Categories of data models

Conceptual (high-level, semantic) data models: Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.)

Physical (low-level, internal) data models: Provide concepts that describe details of how data is stored in the computer.
Record formats, record orderings and access paths
Target computer specialists and not typical end users

Implementation (representational) data models: Emphasizes on how the data is represented in the database or how the data structures are implemented to represent what is modeled  (eg. Relational or OO models)

Database (Implementation) Models

* Hierarchical
* Network
* Relational
* Object-oriented

Hierarchical Model

Represents a hierarchy with the whole at the root and the components forms the child nodes in turn

Thus, all the components or the nodes, taken together form the whole

Network Model

Resembles the hierarchical model with a provision for a record to have more than one parent

An owner record is equivalent to a parent, and a member record s equivalent to a child in the hierarchical model

The difference is that a record can appear as a member in more than one set

Relational Model

* They can manipulate are stored as relations  relational database
* Relational database system devised by Codd in 1970
* An attempt to devise a standard model with a sound mathematical basis
* Most successful & better model than other  database model
SQL query language uses for querying the data

* Examples include:
Oracle, Microsoft Access, FoxPro, MySql, SQLServer etc

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