DBMS Model

Database models:--

As the one fundamental characterstic of database system is "abstraction".

Note:-- Data abstraction is the term refers to abstracting the details of data organization and storage related details and show the essential features which are relevant to the user.

Data models are defined as blueprint or a model view of data items to the users.So there are different types of models are used for representing data in such a manner that is useful more user .

Data models are also defined as ---

A collection of concept that can be used for describing the structure of database

Structure of database we means data types and relationship among data items, data constraints that are applied to the data .

Data models are categorized as:-

High -level or conceptual data model --Provides concepts in such a ways that are merely accepted by the users .In simple way conceptual data models

provides concepts that are closed to the way which are easily understood by many people.

eg:---entity -relationship model

An entity represent the real-world objects or concepts

An attributes are used to represents some property of interest that

further describes an entity or relationship .

A relationship among two or more entities basically represents the association among the entities .

Network and hierarical data models:--

mainly used by the programmers ,who are aware with the queries and structured of the data items

eg:--relation(tables) and relational models .

Low-level or physical data model:----

physical models defines ,how the data items are stored as files in computer.

In relational database model data items are represented in the form of tables :

such as tables is simply the combination of rows and columns:--

Rows:-- each row in databse table represents the one instance of the one type of object described in that table.row is also called touple..

Columns:--column in the table are set of facts .a column is also called an "attribute".

Schemas:--In database ,description of database is called "the database schema".A schema is basically displays such as the names of record types and data items ,and some type of

constraints .