Chapter 2 Database System Concepts and Architecture Presentation

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

Outline b Data Models, Schemas, and Instances • Categories of Data Models • Schemas, Instances, and Database State b DBMS Architecture and Data Independence • The Three-Schema Architecture • Data Independence b Database Languages and Interfaces • DBMS Languages • DBMS Interfaces 2

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

Data Models, Schemas, and Instances b 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 4

Categories of Data Models b Conceptual (high-level) • Provide concepts that are close to the way many users perceive data (Also called entity-based, object-based data models) b 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 b 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 5

Schemas, Instances, and DB State b Database Schema (intension) • The description of a database • Not expected to change frequently b Schema Diagram • A diagrammatic display of (some aspects of) a database schema. b 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 6

The Three-Schema Architecture b Internal Schema • Describes the physical storage structure • Uses a physical data model b Conceptual Schema • Describes the structure of the whole database • Uses a conceptual or an implementation data model b External Schema • Includes a number user views • Uses a conceptual or an implementation data model b Mappings • The process of transforming requests and results between levels 7

The Three-Schema Architecture 8

Data Independence b Logical Data Independence • The capacity to change the conceptual schema without having to change the external schema or application programs b Physical Data Independence • The capacity to change the internal schema without having to change the conceptual schema b 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 9

DBMS Languages b 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 b 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 10

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

DBMS Component Modules 12

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

Tools, Application Environments, and Communications Facilities b CASE tools • Used in the design phase b 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 b Application Development Environments • Provide an environment for developing database applications • Include facilities for database design, GUI development, querying and updating, and application program development b Communications software • Allow users to access database from remote location 14

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