Introduction to DBMS

Database Processing

A DATABASE is an organized collection of related data• McFadden-Hoffer

– a shared collection of logically related data– designed to meet the information needs of multiple users in an organization

• Kroenke– a self-describing collection of integrated records

• self-describing: in addition to the user’s source data, contains a description of its own structure

• collection of integrated records: user data, metadata (data about data), indexes to represent relationships among data and improve performance, data about applications that use the database

• Rob-Coronel– a shared integrated computer structure that houses a collection of

• end-user data--i.e. raw facts of interest to the end-user• metadata through which the data are integrated

DBMSA Database Management System (DBMS) is general purpose software and hardware facility to:– Create, delete, reorganize, and manipulate data in a database– Store, retrieve, share, and maintain data in a database– Maintain relationships between the database components– Provide security and procedures relating to privilege and access.– The integrity of all the updates and transactions that are carried

out.– interface for the access, deletion and addition of data and for

redefining the relationships within the database.A DBMS is a collection of programs that manages the database structure and controls access to the data stored in the database.

DBMS Disadvantages DBMSs are complex; Need for explicit backup and control; Costs associated with development and

operation can be substantial;

Database Systems Types

• Number of Users: – Single-user: usually desktop– Multi-user: workgroup (small); enterprise (large)

• Location:– Centralized: all data stored in a database at a single site– Distributed: database is distributed across several sites

• Type and Use:– Production (transactional): designed to support day-to-day use– Decision Support: designed to make tactical and strategic decisions at

middle- and high-management levels– Decision Support Systems (data warehouse): use of historical data from

many sources to make decisions such as pricing, sales forecasts, marketing positioning (e.g. structural estimates for insurance by underwriters)

DBMS Functions• Data Dictionary Management• Data Storage Management--Data Storage Definition Language (DSDL)• Data Transformation and Presentation• Database Control Language (DBCL)

– Security Management– Multi-User Access Control

• Backup and Recovery Management• Data Integrity Management• Data Access Languages

– Data Definition Language (DDL)– Data Manipulation Language (DML)

• Application Program Interfaces– COBOL, C, PASCAL, Visual Basic– Administrative Utilities

• Data Communication Interfaces– queries, reports, email through web browsers

Database vs. File Systems

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Figure 1.6

DBMSARCHITECTURE

View of DataAn architecture for a database system

Levels of Abstraction• Many views, single

conceptual (logical) schema and physical schema.– Views describe how users see

the data. – Conceptual schema defines

logical structure– Physical schema describes the

files and indexes used.

Schemas are defined using DDL; data is modified/queried using DML.

Physical Schema

Conceptual Schema

View 1 View 2 View 3

Example: University Database

• Conceptual schema: – Students(sid: string, name: string, login: string,

age: integer, gpa:real)– Courses(cid: string, cname:string, credits:integer) – Enrolled(sid:string, cid:string, grade:string)

• Physical schema:– Relations stored as unordered files. – Index on first column of Students.

• External Schema (View): – Course_info(cid:string,enrollment:integer)

Raghu Ramakrishnan

Data Independence

• Applications insulated from how data is structured and stored.

• Logical data independence: Protection from changes in logical structure of data.

• Physical data independence: Protection from changes in physical structure of data.