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Chapter 2: Database System Concepts and Architecture

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

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Chapter 2: Database System Concepts and Architecture

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

  2. 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

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

  4. Data Models, Schemas, and Instances • Data Model • 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

  5. 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

  6. 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

  7. 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 • Uses a conceptual or an implementation data model • Mappings • The process of transforming requests and results between levels

  8. The Three-Schema Architecture

  9. Data Independence • Logical 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

  10. 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

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

  12. DBMS Component Modules

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

  14. 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

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

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