Ch. 1 데이터베이스시스템 (2). Ch.1 Database System 데이터베이스시스템 2 What to Learn Database System Overview Entity-Relationship diagram Relational Data Model Structure

Ch. 1데이터베이스시스템 (2)

Ch.1 Database System 데이터베이스시스템 2

What to Learn Database System Overview Entity-Relationship diagram Relational Data Model

Structure & Constraints SQL language

How to use Commercial DBMS’s MS Access MS SQL Server

Normalization ( 정규화 ) Transaction & Concurrency ( 동시성 )


What to Learn Database and Database system Modeling a real world

Conceptual Modeling Data Modeling Data Structuring

File processing system Advantages of database system


What to Learn Components of a Database system

Database Software (DBMS) Users

Application Programmers, End users, DBA's Hardware (computer)

ANSI database architecture Various types of database system

Central vs. distributed systems Client/server system


Components of a database sys-tem Database

A collection of data to store Software

Database management system (DBMS) Handles all the access to the database

Hardware Computers and hard disks

Users Application programmer End user Database administrator (DBA)


components of a database sys-tem

Real World

system boundary

E-R diagram

conceptualmodeling

logical schema(conceptual view)

physical schema(internal view)

stored database

Operatingsystem

DBMS DDL

DML

view view view

External view


1. Database Logical database

NAME ST_NO ADDRESS DEPT GRADE

송치윤 52015 사당동 컴퓨터 3.3

김구완 53116 홍제동 정보통신 3.1

최재석 56034 양재동 정보관리 3.5

Field, Column, Attribute Record, Row, Tuple File, Table, Relation Record type, Table heading, Relation schema (type) Records, Table body, Relation instance (state)

Physical database Data dictionary (system catalog)


2. Software (DBMS) (1)shielding database users from hard-ware-level details

Functions of DBMS Data definition

Save the schema in the data dictionaryschema detailed definition of the overall database de-signlogical schema, physical schema,external/conceptual mapping, (p.48) conceptual/internal mappingData definition language (DDL) (p.41)


components of a database sys-tem

Real World

system boundary

E-R diagram

conceptualmodeling

logical schema(conceptual view)

physical schema(internal view)

stored database

Operatingsystem

DBMS DDL

DML

view view view

External view


2. Software (DBMS) (2) Data manipulation

Data manipulation language (DML, 데이터 조작어 ) (p.42)

Retrieve, Select ( 검색 ), Insert ( 삽입 ), Delete ( 삭제 ),Update ( 수정 )

Other functions Query optimization ( 질의 최적화 ) Concurrency control ( 동시성 제어 ) Recovery ( 복구 ) Security ( 보안 ) Integrity ( 무결성 )


2. Software (DBMS) (3) Example of query optimization

Students(St_No, Name, Year), 10,000 rowsEnroll(St_No, Subject, Grade) 50,000 rows

Select the enrollment state of first year students.

1) match Student and Enroll tables 50,000 rows select first year students 12,500 rows

2) select first year strudents 2,500 rows match Student and Enroll tables 12,500 rows


2. Software (DBMS) (4) Example of concurrency control

Sales(Prod_No, sale_amount), current value = 30Agent A sold 30, Agent B sold 20The correct value should be 30+30+20 = 80

1) Agent A reads the current value 30, calculates 30+30 Agent B reads the current value 30, calculates

30+20 Agent A updates the record to 60, Agent B updates the record to 50. The sale of 30

is lost.

2) Agent A requests a lock, and reads 30, calculates 30+30

Agent B requests a lock, but waits until the lock is released.

Agent A updates the record to 60, releases the lock

Agent B gets a lock, and reads 60, calculates 60+20

Agent B updates the record to 80, releases the lock


2. Software (DBMS) (5) p.55


3. Users (1) Application programmers

write database application programs in general programming language

host language : general programming language like C++, Visual Basic, C#, Java

embedded language : the language used to send DML to a DBMS

End usersad hoc (unplanned) query user : use a program with which a user

directly send DML command to DBMScanned (planned) query user ; use an easy-to-use program which

was developed by application programmers

Database Administrator (DBA)responsible for the overall control of the database system at a

technical level c.f. : data administrator


3. Users (2) p.43


3. Users (3) DBA’s tasks

Define the logical schema Define the physical schema Define security and integrity constraints Define backup/recovery policies Assist users : provide technical education,

analyze the information requirements of users,

consult application design balance conflicting user requirements

Monitor performance and respond to changing requirements


Goals of database systems Reduce redundancy through integration Sharing Standardization Enhance security and integrity Data independence Data abstraction


Goals of database systems Data independence

Immunity of applications to change in physical represen-tation and access technique

Possible changes in data representationnumbers (real, integer, fixed, floating point)

remember Y2k problemcharacters (ASCII, Unicode)coding system (M or F, 0 or 1)changes in record structure

product(Prod_No, Prod_Name, cost, price,monthlyproduction, monthlysales)

Data abstraction Easy to use (do not worry about physical structures)

select Prod_Name, price, monthlysales from prod-uct;


ANSI/SPARC Architecture p.48


Centralized vs. Distributed database


Centralized vs. Distributed database p.58


Client-Server system p.60 2-tier vs. 3-tier model

Documents

Ch. 1 데이터베이스시스템 (2). Ch.1 Database System 데이터베이스시스템 2 What to Learn Database System Overview Entity-Relationship diagram Relational Data Model Structure