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Fundamentals of
Database Systems
Chapter 1
Database and Database Users
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Introduction
 Basic Definitions
 Database
» A collection of related data
 Data
» Known facts that can be recorded and have an
implicit meaning
 Mini-world (Universe of Discourse, UoD)
» Some part of the real world about which data is
stored in a database
» E.g., student grades and transcripts at a university
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Introduction (cont.)
 Database Management System (DBMS)
» A software package/ system to facilitate the
creation and maintenance of a computerized
database
 Database System
» The DBMS software together with the database
» Sometimes, the applications are also included
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Introduction (cont.)
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Introduction (cont.)
 Example of a Database
 Mini-world for the example: Part of a
UNIVERSITY environment
 Some mini-world entities
» STUDENTs
» COURSEs
» SECTIONs (of COURSEs)
» (academic) DEPARTMENTs
» INSTRUCTORs
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Introduction (cont.)
 Some mini-world relationships
» SECTIONs are of specific COURSEs
» STUDENTs take SECTIONs
» COURSEs have prerequisite COURSEs
» INSTRUCTORs teach SECTIONs
» COURSEs are offered by DEPARTMENTs
» STUDENTs major in DEPARTMENTs
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Introduction (cont.)
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Characteristics of Database
Approach
 Database v.s. File-processing
 Self-contained nature
» A DBMS catalog stores the description of the
database (called meta-data)
» This allows the DBMS software to work with
different databases
 Program-data independence
» Allows changing data storage structures and
operations without having to change the DBMS
access programs
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Characteristics of Database (cont.)
For example, a STUDENT record
» If add another field, Birthday
– File-processing: needs to rewrite the program
– Database system: only change the STUDENT
description, no change to DBMS program
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Characteristics of Database (cont.)
 Data abstraction
» A data model is used to hide storage details and
present the users with a conceptual view of the
database
 Support of multiple views of the data
» Each user may see a different view of the
database, which describes only the data of
interest to that user
» A view may be materialized (stored) or virtual
(definition)
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Characteristics of Database (cont.)
» Different database views reveal different
combinations of data
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Characteristics of Database (cont.)
» Student transcript view
» Course prerequisite view
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Characteristics of Database (cont.)
 Sharing of Data and Multiuser Transaction
Processing
» Allow multiple users to access the database at the
same time
» The DBMS must include concurrency control
software (On-line transaction processing,OLTP)
» e.g., Air-line reservation
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Characteristics of Database (cont.)
 Additional Advantages
 Controlling redundancy
» In file-processing approach, every user group
maintains its own files
e.g., Course registration, Accounting office
» Problems: inconsistency, wasted storage
» In database approach, all user groups are
integrated, no redundancy
» But in some cases, redundancy is useful; need
redundancy controlling to prohibit inconsistency
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Characteristics of Database (cont.)
» Controlled redundancy
» Uncontrolled redundancy
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Characteristics of Database (cont.)
 Enforcing integrity constraints
» Data type constraint
– e.g., Grade: A, B, C, D, E
» Relationship constraint
– e.g., every section record is related to a course record
» Uniqueness constraint
– e.g., CourseNumber
» Note: errors may occur even if integrity
constraints
hold
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– e.g., a student’sDatabase
grade A is wrongly entered C
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Characteristics of Database (cont.)
 Restricting unauthorized access
 Sharing of data among multiple users
 Providing multiple user interfaces
 Representing complex relationships
 Providing backup and recovery
 Potential for enforcing standards
 Reduced application development time
 Flexibility to change data structures
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Characteristics of Database (cont.)
 Availability of up-to-date information
 Economies of scale
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Actors of Database Systems
 Actors on the Scene
 Database administrators
 Database designers
 End users
 System analysts
 Application programmers
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Actors of Database Systems (cont.)
 Workers behind the Scene
 DBMS system designers and implementers
» Design and implement the DBMS modules and
interfaces as a software package
 Tool developers
» Tools are optional packages, e.g., GUI
 Operators and maintenance personnel
» Responsible for the actual running and
maintenance
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When not to use a DBMS
 Main costs of using a DBMS
 High initial investment and possible need for
additional hardware
 Generality that a DBMS provides for
defining and processing data
 Overhead for providing generality, security,
recovery, integrity, and concurrency control
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When not to use a DBMS (cont.)
When a DBMS may be unnecessary
 The database and applications are simple,
well defined, and not expected to change
 There are stringent real-time requirements
that may not be met because of DBMS
overhead
 Multiple-user access to data is not required
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