DatabaseCSIE NUK1 Fundamentals of Database Systems Chapter 1 Database and Database Users

DatabaseCSIE NUK2 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

DatabaseCSIE NUK3 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

DatabaseCSIE NUK4 Introduction (cont.)

DatabaseCSIE NUK5 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

DatabaseCSIE NUK6 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

DatabaseCSIE NUK7 Introduction (cont.)

DatabaseCSIE NUK8 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

DatabaseCSIE NUK9 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

DatabaseCSIE NUK10 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)

DatabaseCSIE NUK11 Characteristics of Database (cont.) »Different database views reveal different combinations of data

DatabaseCSIE NUK12 Characteristics of Database (cont.) »Student transcript view »Course prerequisite view

DatabaseCSIE NUK13 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

DatabaseCSIE NUK14 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

DatabaseCSIE NUK15 Characteristics of Database (cont.) »Controlled redundancy »Uncontrolled redundancy

DatabaseCSIE NUK16 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 – e.g., a student’s grade A is wrongly entered C

DatabaseCSIE NUK17 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

DatabaseCSIE NUK18 Characteristics of Database (cont.)  Availability of up-to-date information  Economies of scale

DatabaseCSIE NUK19 Actors of Database Systems  Actors on the Scene  Database administrators  Database designers  End users  System analysts  Application programmers Software Engineers

DatabaseCSIE NUK20 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

DatabaseCSIE NUK21 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

DatabaseCSIE NUK22 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