A major purpose of a database system is to provide users with an abstract view of the data.

Conceptual View

External View

For the system to be usable, it must not retrieve data efficiently

describes what data are stored in the database, and what relationships exist among those data

The highest level of abstraction describes only part of the entire database

The lowest level of abstraction describes how the data are actually stored

describes the entire database in terms of a small number of relatively simple structures

ANSI: American National Standards Institute

Change to internal level shouldn’t affect the conceptual level

The overall design of the database is called the database instance

The collection of information stored in the database at a particular moment is called … of the database

A database system is a collection of interrelated data and a set of programs that prevent users to access and modify these data.

Specified during the database design process

Not expected to change frequently

data model :a collection of concepts that can be used to describe the structure of a database

The structure of a database mean the data types, relationships, and constraints

was developed by IBM and North American Rockwell known as Information Management System.

This model is the first DBMS model

It represents data as relations or tables

Object Model :It replaces the hierarchical tree with a graph.