Introduction to Database Management System 電機三 趙上鋒

Outline  What is DBMS?  What can DBMS do?  How to design a database?  How to use DBMS?  Conclusion  Reference

What is DBMS?

Data v.s. Information  Data  Anything stored without summarized or analyzed.  Information  Data that has been proceeded to be meaningful for users.

Example Data Information

Database  Stores organized data so that you can query from it or update it.  Like an electrical shelf to put data with organization.

From user to data Teacher (user) Application x Database data Student (user) Application x

What is DBMS?  Database Management System  DBMS is software to store and manage data, so applications don’t have to worry about them.  Like a person who search the dictionary for you.

Relation between App & DBMS Teacher (user) Application x data Student (user) Application x View1 View2 Conceptual schema Physical schema DBMS

What can DBMS do?

DBMS can Do These…  Store huge amount of data ( eg. 100+GB )  Store data for long period of time  Manage data on permanent storage.  Efficient database operation  B+ Tree indexing  Hash-based indexing  Allow people to query & update data  Support query language.

More Requirement  Protect from unauthorized access  Security!  Protect from system crash  Crash recovery  Support many users to access the database at the same time  Concurrency control  Allow administrator to easily change data schema  Protect from incorrect input

If we don’t use DBMS  Applications have to stores data as files  32-bit addressing (5GB) is insufficient to address 100GB+ data file  Write special code to:  support different queries  protect data from multiple users and concurrent access  protect against data loss / corruption as result of system crashes

If we don’t use DBMS (cont’d)  Other issues:  Rewrite applications when data schema changes  Password-based authorization is insufficient  Optimize applications for efficient access and query  Easier to use a DBMS to handle these issuse!

How to design a database

Data Model  A data model is a collection of concepts for describing data.  Entity-relation (ER) model  Proposed by Peter Chen (BS NTU EE ‘68) in 1976  popular for conceptual design  Relational model  Object-oriented model  A schema is a description of a particular collection of data in a given data model.  Eg. How to describe a book?

Some example for ER-modal user idpassword order num Entity set key attribute relation book ISBN name author price

Relational Model  Most widely used today  Microsoft SQL Server  Oracle  MySQL  SyBase  IBM DB2  Microsoft Office Access

Why People Like It  Simple  Each relation is represented as a table of rows and columns  Easy to understand  Ease of expressing complex query (using SQL) on the data  Efficient query evaluation (using query optimization)

Example of Relation  A relation has two parts:  Relational Schema defines column heads of the table.  Relational Instance contains the data rows (called tuples or records) of the table. ISBNnameauthorprice 羊肉爐不是故意的 LogyDog 奼紫嫣紅牡丹亭：四百年青春之夢白先勇 孽子白先勇 270

Example of Relation  Field  Also called an attribute or a column  Key  a set of minimal fields that can uniquely identify a tuple in a relation ISBNnameauthorprice 羊肉爐不是故意的 LogyDog 奼紫嫣紅牡丹亭：四百年青春之夢白先勇 孽子白先勇 270

Convert from ER-Model to Relational Model idpassword user id password order num book ISBN name author price ISBNnameauthorprice idISBNnum userbook order

How to use DBMS?

SQL  Structured Query Language  Developed by IBM (system R) in the 1970s  Current standard: SQL-99  DDL: Data Definition Language  DML: Data Manipulation Language

SQL Basic Commands  DDL  create table: create a table  drop table: delete a table  alter table: alter a field in a table  DML  insert: add a record  delete: delete a record  update: change field values in a record  select: query data satisfying some condition

Example of create table & drop table create table book( ISBN integer, name char(255), author char(127), price integer, primary key(ISBN) ) drop table book ISBNnameauthorprice

Example of alter table alter table book add m_price integer alter table book drop m_price ISBNnameauthorprice m_ price

Example of insert insert into book( ISBN, name, author, price ) values ( , “ 羊肉爐不是故意的 ”, “LogyDog”, 200 ) ISBNnameauthorprice ISBNnameauthorprice 羊肉爐不是故意的 LogyDog200

Example of delete delete from book where author = ‘ 白先勇 ’ ISBNnameauthorprice 羊肉爐不是故意的 LogyDog 奼紫嫣紅牡丹亭：四百年青春之夢白先勇 孽子白先勇 270

Example of update update book as b set b.name = ‘ 羊肉爐不是故意的 ’ where b.author = ‘LogyDog’ update book as b set b.price = b.price * 0.9 ISBNnameauthorprice 羊肉爐是故意的 LogyDog 奼紫嫣紅牡丹亭：四百年青春之夢白先勇 孽子白先勇 270 羊肉爐不是故意的

Example of select select book as b where b.price<300 and author=‘ 白先勇 ’ ISBNnameauthorprice 羊肉爐不是故意的 LogyDog 奼紫嫣紅牡丹亭：四百年青春之夢白先勇 孽子白先勇 270

Conclusion

Reference  Database Management System, 3 rd Ed., by R&G  dex.html - by Hao-hua Chu dex.html  Computer Science -- An Overview, 7 th Ed, by J. Glenn Brookshear