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Refers to the content of a database at a moment in time.

Conceptual

In many DBMSs, the ____ is also used to define internal and external schemas (views).

add a record or data item

Specialized Servers with Specialized functions

UI and apps

ER

the internal schema may be changed when certain file structures are reorganized or new indexes are created

In some DBMSs, separate (SDL) and (VDL) are used to define internal and external schemas.

Implementation

The actual data stored in a database at a particular moment in time.

describe physical storage structures and access paths

Data extracted from the internal DBMS level is reformatted to match the user’s external view

Used to specify database retrievals and updates

When a schema at a lower level is changed, the application programs need not be changed

changes very infrequently

Used by the DBA

SQL

Common for Web applications

May be used in a standalone way or may be embedded in a programming language

دا تعريف ايه؟

relational language SQL

Low Level or Procedural Languages:

Provide concepts that describe details of how data is stored in the computer

The capacity to change the conceptual schema without having to change the external schemas and blabla

Typically uses a physical data model

Different type of databases connected

can be applied directly (called a query language)

The description of a database

A state that satisfies the structure and constraints of the database.

must be embedded in a programming language

extension

Changes to constraints

Relational DBMS servers are often called

Expand the DB

Provide concepts that are close to the way many users perceive data

Physical

single computer with one database

An illustrative display of (most aspects of) a database schema.

Uses implementation data model.

Two-tier Architecture Can Enhance Security:

Programs refer to an internal schema, and are mapped by the DBMS to the internal schema for execution.

Combines everything into single system including DBMS software, hardware, application programs, andUI

Includes descriptions of the database structure, data types, and the constraints on the database

SDL is typically realized via DBMS commands provided to the DBA and database designers

When a schema at a lower level is changed,nothing has to be changed in a DBMS that fully supports data independence.

Used to specify the conceptual schema of a database.

Query and transaction functionality

Reduce the DB

SQL

High-Level or Non-procedural Languages

(e.g indexes).

Same type of databases connected

Conceptual

describe the structure and constraints for the whole database for a community of users.

occurrence or snapshot

s (e.g. relational data models used in many commercial systems).

Mappings among schema levels are needed to transform requests and data.

intension

Provide concepts that fall between the above two, used by many commercial DBMS implementations

User can't connect through a remote terminal in a Centralized DBMS

be embedded in a generalpurpose programming language (host language), such as C++, or Java.

Usually uses the same data model as the conceptual schema.

changes every time the database is updated.

Used by database designers

remove a record or data item

When a schema at a lower level is changed The higher-level schemas themselves are unchanged.

Reorganization of physical files

The capacity to change the internal schema without having to change the conceptual schema or external schema.

Uses conseptual or implementation data model.

Physical

Refers to the database state when it is initially loaded into the system

describe the various user views.

multiple computers, multiple DBs