Chapter 1 1

CS 262-557

Introduction to Database

Systems

Chapter 1 2

Chapter 1

Databases and Database

Users

Chapter 1 3

What is a Database?

• A collection of related data.

• It contains data specific to part of the real world, a miniworld.

• Consequently, it is a logically coherent collection of data.

• It is maintained for specific applications.

Chapter 1 4

Address Book

Alan Arkin

200 Olive Street

Ann Arbor, MI 48104

313-555-1212

Birthday May 10th

. . .

Mary Ziegler

341 Einstein Drive

Berkeley, CA 94703

510-555-1234

Annivsy: July 12th

Chapter 1 5

September 1998

Sun Mon Tues Wed Thurs Fri Sat1 2 3 4 5

6 7 8 9 10John’sBday

11 12

13 14 15 16 17 18 19

20 21 22 23 24 25 26

27Sue’sAnnvy

28 29 30

Chapter 1 6

Index on Cities

Ann Arbor

Ann Arbor

Berkeley

Berkeley

Compton

Allan Arkin

John Doe

Sue Smith

Mary Ziegler

John Law

Chapter 1 7

Stages in the Lifeof a Database

• Definition: specifying structures of tables and data to be stored.

• Construction: populating tables with data.

• Manipulation: queries, updates, deletes, etc.

Chapter 1 8

• A DBMS (database management system) is a general-purpose software that enables users to define, construct and maintain various databases. ie. Oracle, Dbase IV

• However, databases have been implemented using a high-level language to define a collection of files. Using programs to access this files. This is traditional file processing.

Chapter 1 9

Fig 1.1

Chapter 1 10

• A database system, which consists of a database together with DBMS software, is the complete environment in which a user operates.

Chapter 1 11

Fig 1.2

Chapter 1 12

Hypothetical situation: Smith and Brown are on probation and need approval from the instructor of each course that they scored a C or less.

What are the names of these courses?

Who are the instructors?

Suggested changes to tables if these queries are frequent.

Chapter 1 13

What Problems could the University have regarding access

to these tables?

Chapter 1 14

Solution

• “Virtual” tables or views allows the organization to selectively provide access to information while avoiding concurrency problems.

• Views also allow for the creation of dynamic summary views of information.

Chapter 1 15

fig 1.4

Chapter 1 16

Characteristics of the DBMSApproach

• Self-describing nature: Together with each database is stored a system catalog which is a separate entity containing information about each table in the database, types of each data item I.e. metadata!

Chapter 1 17

• Insulation between programs & data: Consequence of using metadata. In traditional file processing the structure of the file is embedded in the access program, while with DBMS the structure of a file is defined separately in the system catalog, and is transparent to the access program.

E.g.. in the University database if we added extra fields in GRADE_REPORT table, all programs that access this table would have to be rewritten! This is not true with a DBMS.

Chapter 1 18

• Support of multiple views: A view may be a subset of the database, or may contain virtual data that is not explicitly stored, but instead it is derived. i.e. TotalHours in STUDENT_DUES.

• Sharing of data: A multi-user DBMS provides concurrency control software to allow multiple users to simultaneously access data. Such as bank accounts and airline reservations.

Chapter 1 19

• Control of Redundancy: There are 3 main problems with redundancy:– duplication of effort– waste of space– possible inconsistency

• In the DBMS approach, redundancy is regulated by centralizing the data in one database, and providing various user groups with the views they need. However, controlled redundancy may sometimes be desirable

Chapter 1 20

• Security & Authorization Mechanisms: Consequence of centralization. The DBA may restrict privileges (retrieve, update,etc) by either database, user or user’s role.

• Enforcing integrity constraints: A DBMS provides capabilities to enforce constraints or business rules I.e. each student must have a unique studentnumber.

• Providing Backup & Recovery: A DBMS provides facilities to recover from either software or hardware failures.

Chapter 1 21

DBMS Personnel

• Tool Developers

• DBMS Designers

• Database Administrator (DBA)

• System Analysts

• End Users– Casual - occasional high level use– Parametric- frequent canned transactions– Sophisticated - frequent high level use