Ch. 1 데이터베이스시스템 (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 )

Ch.1 Database System 데이터베이스시스템 3 What to Learn Database and Database system Modeling a real world  Conceptual Modeling  Data Modeling  Data Structuring File processing system Advantages of database system

Ch.1 Database System 데이터베이스시스템 4 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

Ch.1 Database System 데이터베이스시스템 5 Components of a database system 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)

Ch.1 Database System 데이터베이스시스템 6 components of a database system Real World system boundary E-R diagram conceptual modeling logical schema (conceptual view) physical schema (internal view) stored database Operating system DBMS DDL DML view view view External view

Ch.1 Database System 데이터베이스시스템 7 1. Database Logical database NAMEST_NOADDRESSDEPTGRADE 송치윤 사당동컴퓨터 3.3 김구완 홍제동정보통신 3.1 최재석 양재동정보관리 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)

Ch.1 Database System 데이터베이스시스템 8 2. Software (DBMS) (1) shielding database users from hardware-level details Functions of DBMS  Data definition Save the schema in the data dictionary schema detailed definition of the overall database design logical schema, physical schema, external/conceptual mapping, (p.48) conceptual/internal mapping Data definition language (DDL) (p.41)

Ch.1 Database System 데이터베이스시스템 9 components of a database system Real World system boundary E-R diagram conceptual modeling logical schema (conceptual view) physical schema (internal view) stored database Operating system DBMS DDL DML view view view External view

Ch.1 Database System 데이터베이스시스템 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 )

Ch.1 Database System 데이터베이스시스템 Software (DBMS) (3)  Example of query optimization Students(St_No, Name, Year), 10,000 rows Enroll(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 students12,500 rows 2) select first year strudents 2,500 rows match Student and Enroll tables 12,500 rows

Ch.1 Database System 데이터베이스시스템 Software (DBMS) (4)  Example of concurrency control Sales(Prod_No, sale_amount), current value = 30 Agent A sold 30, Agent B sold 20 The correct value should be = 80 1) Agent A reads the current value 30, calculates Agent B reads the current value 30, calculates 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 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 Agent B updates the record to 80, releases the lock

Ch.1 Database System 데이터베이스시스템 Software (DBMS) (5) p.55

Ch.1 Database System 데이터베이스시스템 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 users ad hoc (unplanned) query user : use a program with which a user directly send DML command to DBMS canned (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

Ch.1 Database System 데이터베이스시스템 Users (2) p.43

Ch.1 Database System 데이터베이스시스템 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

Ch.1 Database System 데이터베이스시스템 17 Goals of database systems Reduce redundancy through integration Sharing Standardization Enhance security and integrity Data independence Data abstraction

Ch.1 Database System 데이터베이스시스템 18 Goals of database systems Data independence  Immunity of applications to change in physical representation and access technique  Possible changes in data representation numbers (real, integer, fixed, floating point) remember Y2k problem characters (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 product;

Ch.1 Database System 데이터베이스시스템 19 ANSI/SPARC Architecture p.48

Ch.1 Database System 데이터베이스시스템 20 Centralized vs. Distributed database

Ch.1 Database System 데이터베이스시스템 21 Centralized vs. Distributed database p.58

Ch.1 Database System 데이터베이스시스템 22 Client-Server system p.60 2-tier vs. 3-tier model