บทที่ 2
ระบบฐานข้ อมูล
อ. ดร. ชุรี เตชะวุฒิ
CS (204)321
ระบบฐานข้อมูล 1 (Database System I)
เนื้อหา
1) ลักษณะการประมวลผลของระบบฐานข้อมูล (Major characteristic of
database approach)
สภาพแวดล้อมของระบบฐานข้อมูล (Database system environment)
3) ประเภทของการประยุกต์ฐานข้อมูล (The range of database application)
4) สถาปั ตยกรรมแบบรับและให้บริ การ (Client/Server Architecture)
5) ประโยชน์ของการใช้ระบบจัดการฐานข้อมูล
6) องค์ประกอบของระบบจัดการฐานข้อมูล
7) หน้าที่ของระบบจัดการฐานข้อมูล
8) หลักการของระบบฐานข้อมูลและสถาปั ตยกรรม
2)
Major Characteristics of Database Approach
 Self-describing nature of a database system
 A DBMS catalog stores the description of the database. The
description is called meta-data. This allows the DBMS software to work
with different databases
A traditional file processing can work with only one specific database.
The description of the database is declared by data definition in the
application program. For example, C and C++ program have “struct” or
“class” declaration.
 Insulation between program and data
 Allows changing data storage structures without having to change the
DBMS access programs called program-data independence.
Changing in the structure of data files, embedded in the access
programs, requires to change all programs that access this file.
Major Characteristics of Database Approach
 Data abstractions
 A data model is used to hide storage details and present the user with
a conceptual view of the database. (data model – logical concepts –
objects, properties, relationships)
In traditional file processing, the representation of the structure of data
files is very complicated. Details that are not of interest cannot be
hidden.
 Support of multiple views of data
 Each user may see a different view of the database, which describes
only the data of interest to that user.
A traditional file processing cannot provide a different view of the
database.
Major Characteristics of Database Approach
 Sharing of data and multiuser transaction processing
 DBMS allows multiple users to access the database at the same time.
DBMS controls concurrent transactions from multiple users to operate
correctly without interference so that data are updated correctly.
A traditional file processing limits data sharing.
Database System Environment
Users/Programmers
DATABASE
SYSTEM
Application Programs/Queries
DBMS
SOFTWARE
Software to Process Queries/Programs
Software to Access Stored Data
Stored Database
Definition (Meta-Data)
Stored Database
Source: Elmasri R. & Navathe S.B. (1994) Fundamentals of database systems
Examples of Database
 A UNIVERSITY database for maintaining information concerning
students, courses, and grades in a university environment.
 To define this database, we must specify
1)
The structure of the records.
For example, each STUDENT record includes data to
represent the student’s
Name,
StudentNumber,
Class (freshman or 1, sophomore or 2,…), and
Major (MATH, computer science or COSC, …).
Examples of Database
2)
A data type for each data element within record.
e.g.
Name of STUDENT is a string of alphabetic characters,
StudentNumber of STUDENT is an integer,
Grade of GRADE_REPORT is a single character from the set
{A,B,C,D,F,I},
Class of a STUDENT as 1 for freshman, 2 for sophomore, 3 for junior,
4 for senior, and 5 for graduate student.
Examples of Database
 To construct the UNIVERSITY database, we store data to represent
each student, course, section, grade report, and prerequisite as a record
in the appropriate file. Records in the various files may be related to one
another.
 Database manipulation involves querying and updating. Example of
query is “retrieve all courses and grades of Smith”.
Examples of Database
STUDENT
COURSE
Name
StudentNumber
Class
Major
Smith
17
1
COSC
Brown
8
2
COSC
CourseName
CourseNumber
Intro to Computer Science
COSC1310
4
COSC
Data Structures
COSC3320
4
COSC
Discrete Mathematics
MATH2410
3
MATH
Database
COSC3380
3
COSC
PREREQUISITE
CreditHours Department
CourseNumber
PrerequisiteNumber
COSC3380
COSC3320
COSC3380
MATH2410
COSC3320
COSC1310
Source: Elmasri R. & Navathe S.B. (1994) Fundamentals of database systems
Examples of Database
SECTION
SectionIdentifier
CourseNumber
Semester
Year
Instructor
85
MATH2410
Fall
91
King
92
COSC1310
Fall
91
Anderson
102
COSC3320
Fall
92
Knuth
112
MATH2410
Fall
92
Chang
119
COSC1310
Fall
92
Anderson
135
COSC3380
Fall
92
Stone
GRADE_REPORT
StudentNumber
SectionIdentifier
Grade
17
112
B
17
119
C
8
85
A
8
92
A
8
102
B
8
135
A
Source: Elmasri R. & Navathe S.B. (1994) Fundamentals of database systems
Database System Environment
องค์ประกอบย่อย 5 ส่ วน
 ส่ วนอุปกรณ์ (Hardware) ได้แก่ Personal computer Mainframe Computer
network Printer และอื่นๆ
 ส่ วนชุ ดคาสั่ ง (Software) ได้แก่ Operating system DBMS และ Application
program
 ระเบียบวิธีปฏิบัติ (Procedure) คือคาสั่งหรื อกฎเกณฑ์ที่ใช้ในการออกแบบและ
วิธีการใช้ระบบฐานข้อมูล
 ข้ อมูล คือ ข้อเท็จจริ งที่จะนาไปบันทึกในฐานข้อมูล อาจเป็ นข้อมูลดิ บที่จะถูกนาไป
ประมวลผลและสร้างเป็ นสารสนเทศ
 บุคลากร (People) คือ บุคคลที่เกี่ยวข้องกับการทางานระบบฐานข้อมูล
Different Types of Database Users
 Workers on the scene
Persons whose job involves daily use of a large database.
1)
Database administrators (DBA)
Responsible for managing the database system – authorizing,
coordinating and monitoring.
2)
Database designers
Responsible for designing the database – identifying and choosing
appropriate structures.
3)
End users
The persons that use the database for querying, updating,
generating reports, etc.
Different Types of Database Users
3)
End users
The persons that use the database for querying, updating,
generating reports, etc. There are several categories of end users.
3.1. Casual end users: They occasionally access the database.
3.2. Naïve or parametric end users: They perform canned
transaction. e.g. bank teller or reservation clerk.
3.3. Sophisticated end users: They familiarize with DBMS and
implement complex applications.
3.4. Stand-alone users: They maintain personal database by using
ready-made program packages.
4)
System analysts and application programmers
They determine requirements, design, and implement canned
transactions for parametric user.
Different Types of Database Users
 Workers behind the scene
Persons whose job involves design, development, operation, and
maintenance of the DBMS software and system environment.
1)
DBMS designers and implementers
Design and implement the DBMS modules and interfaces as a
software package.
2)
Tool developers
Design and implement tools that facilitate the use of DBMS
software. Tools include design tools, performance tools, special
interfaces, etc.
3)
Operators and maintenance personnel
They responsible for the actual running and maintenance of the
hardware and software environment for the database system.
Database Architectures|Client/Server Architecture
user
client
Application
Application client
network
Database system
user
network
server
Application server
Database system
Two-tier architecture
Three-tier architecture
Source: Silberschatz A., Korth, H.F. & Sudarshan S. (2006) Database system concepts.
Database Architectures|Client/Server Architecture
 Two Tier Client-Server Architectures
 Application on client machine invokes database system functionality
at the server machine through query language statements.
 Application program interface like ODBC (Open Database
Connectivity) and JDBC (Java Database Connectivity) are used for
interaction.
 Three Tier Client-Server Architectures
 Client machine communicates with application server only which
means it does not contain any direct database calls.
 Application server communicates with a database system to access
data.
 Appropriate for large applications, and web applications.
ประโยชน์ ของการใช้ ระบบจัดการฐานข้ อมูล
มีดงั นี้
 การควบคุมความซ้ าซ้อนของข้อมูล (Controlling data redundancy)
 การหลีกเลี่ยงความขัดแย้งของข้อมูล (Data inconsistency)
 การใช้ขอ
้ มูลร่ วมกัน (Sharing of data)
 การควบคุมมาตรฐาน (Enforcement of standard)
 การบังคับใช้กฎความคงสภาพ (Enforcement of integrity constraints)
 ความเป็ นอิสระของข้อมูล (Program-data independence)
 ความง่ายในการพัฒนา (Reduced application development time)
 การสารองข้อมูลและการฟื้ นสภาพข้อมูล (Backup and recovery)
 การเข้าถึงและเรี ยกใช้ขอ
้ มูลได้หลากหลายวิธี (Multiple user interface)
องค์ ประกอบของระบบจัดการฐานข้ อมูล
Users/Programmers
DATABASE
SYSTEM
Application Programs/Queries
DBMS
SOFTWARE
Report writer/Report generator
Queries processor
Security system
Database engine
Stored Database
Definition (Meta-Data)
Stored Database
หน้ าทีข่ องระบบจัดการฐานข้ อมูล
มีดงั นี้
 การจัดการพจนานุกรมข้อมูล (Data dictionary management)
 การจัดการหน่วยเก็บข้อมูล (Data storage management and transformation)
 การจัดการความปลอดภัย (Security management)
 การจัดการความคงสภาพของข้อมูล (Data integrity management)
 การควบคุมภาวะการทางานพร้อมกัน (Multi-user access control)
 การสารองข้อมูลและการฟื้ นสภาพข้อมูล (Backup and recovery management)
 ภาษาสาหรับเข้าถึงฐานข้อมูล (Database access language)
 การติดต่อประสานกับฐานข้อมูล (Database communication interface)
หลักการของระบบฐานข้ อมูลและสถาปัตยกรรม
Data Models
 Data model
“A set of concepts that can be used to describe the structure of a
database (data types and relationships) and certain constraints that
the database should obey.”
 Data model operations
“Operations for specifying database retrievals and updates by
referring to the concepts of the data model.”
Operations on the data model may include basic operations and
user-defined operations.
(e.g. A user-defined operation is COMPUTE_GPA which can be
applied to a STUDENT object.)
Data Models
 Categories of data models
1) Conceptual (high-level, semantic) data models:
Provide concepts that are close to the way many users perceive data.
2) Physical (low-level, internal) data models:
Provide concepts that describe the details of how data is stored in the
computer.
3) Implementation (representational) data models:
Provide concepts that fall between above two, balancing user views with
some computer storage details.
Schemas VS. Instances
 In any data model it is important to distinguish between the description
of the database and the database itself.
 Database schema (or meta-data)
“The description of database. It includes description of database
structure and the constraints that should hold on the database.”
The database schema is specified during database design and is not
expected to change frequently.
e.g.
Name: string
StudentNumber: string
Class: integer
Major: string
Schemas VS. Instances
 Schema diagram
“A diagrammatic display of a database schema – structure of each record
type (not the actual instances of a record).”
STUDENT
Name StudentNumber
Class
COURSE
CourseName CourseNumber
PREREQUITSITE
CourseNumber
Major
CreditHours
Department
PrerequisiteNumber
SECTION
SectionIdentifier CourseNumber
Semester
GRADE_REPORT
StudentNumber SectionIdentifier
Grade
Year
Instructor
Schemas VS. Instances
 Schema construct
“An object within the schema.”
e.g. STUDENT, COURSE.
 Database instances
“The actual data stored in a database at a particular moment in time.
Also called database state or occurrence.”
Many database instances can be constructed to correspond to a
particular database schema.
Schemas VS. Instances
Define a new DB
Data firstly
loaded
Specify DB schema
DBMS
catalog
Update
operation
Database
Database
Database
empty state
initial state
DBMS
ensures
valid state
Schemas VS. Instances
 Distinction
The database schema does not frequently change, but the
database state changes every time the database is updated.
Schema is also called intension, whereas state is called extension.
Three-Schema Architecture
 The three-schema architecture was proposed to support DBMS
characteristics of :
Program-data independence.
Supporting multiple views of the data.
 The goal of the three-schema architecture is to separate the user
applications and the physical database.
Three-Schema Architecture
 Schema can be defined at the following three level.
1) Internal schema at the internal level
Describes physical storage structures and access paths.
Typically uses a physical data model.
2) Conceptual schema at the conceptual level
Describes the structure (such as entities, data type, relationship) and
constraints for the whole database.
Uses a conceptual or implementation data model.
3) External schemas at the external level
Describes the various user views.
Usually uses the same data model as the conceptual level.
Three-Schema Architecture
END USERS
External level
Conceptual level
Internal level
EXTERNAL
VIEW1
EXTERNAL
VIEWn
CONCEPTUAL SCHEMA
INTERNAL SCHEMA
STORED DATABASE
Source: Elmasri R. & Navathe S.B. (1994) Fundamentals of database systems.
Three-Schema Architecture
 Mappings among schema levels are needed to transform requests
and data.
If the request is a database retrieval, the data extracted from the
stored database must be reformatted to match the user’s external
view.
 Programs refer to an external schema, and are mapped by the
DBMS to the internal schema for execution.
 Notice that the three schemas are only descriptions of data; the only
data that actually exists is at the physical level.
Data Independence
 Two types of data independence:
1)
Logical data independence
The capacity to change the conceptual schema without having to
change the external schemas and their application programs.
2)
Physical data independence
The capacity to change the internal schema without having to
change the conceptual (or external) schema.
Data Independence
 When a schema at a lower level is changed, only the mappings
between this schema and higher-level schemas need to be changed in a
DBMS that fully supports data independence.
 The higher-level schemas themselves are unchanged. Therefore, the
application programs need not be changed since they refer to the external
schemas.
Three-Schema Architecture
END USERS
EXTERNAL
VIEW1
Logical data independence
External level
Conceptual level
EXTERNAL
VIEWn
CONCEPTUAL SCHEMA
Physical data independence
Internal level
INTERNAL SCHEMA
STORED DATABASE
Source: Elmasri R. & Navathe S.B. (1994) Fundamentals of database systems.
DBMS Language
Once the design of a database is completed and a DBMS is chosen to
implement the database:
 Data Definition Language (DDL) is used by the DBA and by
database designers to define the conceptual schema for the
database and any mapping between the two.
 Storage Definition Language (SDL) is used to specify the internal
schema.
 View Definition Language (VDL) are used to specify external schema user views and their mappings to the conceptual schema.
DBMS Language
Once the database schemas are compiled and the database is populated
with data:
 Data Manipulation Language (DML) are used to specify database
retrievals and updates.
 DML commands (data sublanguage) can be embedded in a generalpurpose programming language (host language), such as COBOL, C or
an Assembly Language.
 In object-oriented systems, the host and data sublanguages typically
form one integrated language such as C++.
 Alternatively, a high-level DML used in stand-alone interactive manner is
called a query language.
DBMS Language
 Types of DML
1) Procedural DML (record-at-a-time or low-level DML)
Must be embedded in a programming language.
Typically retrieve individual records from the database, and use looping
and other constructs of the host programming language to retrieve
multiple records.
Specify how to retrieve data.
e.g. COBOL, C, etc.
DBMS Language
2) Declarative or Non-procedural DML (set-at-a-time or high-level DML)
Use as a stand-alone query language or embedded in a programming
language.
Typically retrieves information from multiple related database records in
a single command.
Specify what data to retrieve than how to retrieve.
Also called declarative languages.
e.g. SQL