Chapter 2: Database System Concepts and Architecture Presentation slides for DATABASE SYSTEMS by Muhammad Waheed Aslam KFUPM Information & Computer Science Department

Outline Data Models, Schemas, and Instances Categories of Data Models Schemas, Instances, and Database State DBMS Architecture and Data Independence The Three-Schema Architecture Data Independence Database Languages and Interfaces DBMS Languages DBMS Interfaces

Outline The Database System Environment DBMS Component Modules Database System Utilities Tools, Application Environments, and Communications Facilities Classification of Database Management Systems

Data Models, Schemas, and Instances A collection of concepts that can be used to describe the structure of a database By the structure we mean the data types, relationships, and constraints that should hold on the data Also includes basic operations for specifying retrievals and updates on the database It is becoming more common to include concepts to specify the dynamic aspect or behavior of a database application

Categories of Data Models Conceptual (high-level) Provide concepts that are close to the way many users perceive data (Also called entity-based, object-based data models) Physical (low-level) Provide concepts that describe details of how data is stored in the computer Meant for computer specialists, not for typical end users Implementation (representational) Provide concepts that may be understood by end users but that are not too far removed from the way data is organized within the computer Hide some details of data storage but can be implemented on a computer system in a direct way

Schemas, Instances, and DB State Database Schema (intension) The description of a database Not expected to change frequently Schema Diagram A diagrammatic display of (some aspects of) a database schema. Database State (extension) The data in the database at a particular moment of time Also called the current set of occurrences or instances Every update operation changes the database from one state to another

The Three-Schema Architecture Internal Schema Describes the physical storage structure Uses a physical data model Conceptual Schema Describes the structure of the whole database Uses a conceptual or an implementation data model External Schema Includes a number user views Mappings The process of transforming requests and results between levels

The Three-Schema Architecture

Data Independence Logical Data Independence Physical Data Independence The capacity to change the conceptual schema without having to change the external schema or application programs Physical Data Independence The capacity to change the internal schema without having to change the conceptual schema Advantages and disadvantages The three -Schema Architecture can make it easier to achieve true data independence Mappings create an overhead during compilation or execution of a query or a program Not implemented fully by DBMSs

DBMS Languages Data Definition Language (DDL) Used by the DBA and database designers to define the conceptual schema of a a database In many DBMSs, the DDL is also used to define the internal and external schemas In some DBMSs, separate storage definition (SDL) and view definition language (VDL) are used to define internal and external schemas Data Manipulation Language (DML) DML commands can be used as stand-alone (query language) or can be embedded within a general-purpose language Procedural DML - allows user to tell system exactly how to manipulate data Non-Procedural DML - allows user to state what data is needed rather than how it is to be retrieved

DBMS Interfaces Menu-based Interfaces for Browsing Forms-based Interfaces Graphical User Interfaces Natural Language Interfaces Interfaces for Parametric Users Interfaces for The DBA

DBMS Component Modules

Database System Utilities Loading Backup File Reorganization Performance monitoring Other Utilities Sorting files Handling data compression Monitoring access by users

Tools, Application Environments, and Communications Facilities CASE tools Used in the design phase Expanded Data Dictionary(information repository) Stores catalog information about schemas and constraints Stores other information such as design decisions, usage standards, application program descriptions, and user information Application Development Environments Provide an environment for developing database applications Include facilities for database design, GUI development, querying and updating, and application program development Communications software Allow users to access database from remote location

Classification of DBMSs Data Model Number of Users Number of Sites Cost Types of Access Path Purpose