Database Systems: A practical approach to design, implementation and
management. 5th Edition. Addison Wesley. Recommended. Textbook. Date, C.J.
(1999).
G64DBS Database Systems Tim Brailsford
G64DBS Module • • • •
Assessment • Exam - 75% • Coursework - 25%
Recommended Textbook Date, C.J. (1999). An Introduction to Database Systems. 7th Edition. Addison Wesley.
Lectures
• •
Mondays, 3pm in LT2 Fridays, 4pm in LT3
Labs - TBA
• •
Will NOT start until approximately Week 4 Wednesdays, 2-4pm in A32
Tim Brailsford (
[email protected]) James Goulding
Recommended Textbook Connolly, T. & Begg, C. (2009). Database Systems: A practical approach to design, implementation and management. 5th Edition. Addison Wesley.
Recommended Textbook Rob, P. Coronel, C. & Crockett, K. (2008). Database Systems: design, implementation & management. 7th Edition. Thompson Learning.
Recommended Textbook Mana Takahashi. (2008). The Manga Guide to Databases. English Edition. No Starch Press.
What is a Database? •
“A set of information held in a computer” Oxford English Dictionary
•
“One or more large structured sets of persistent data, usually associated with software to update and query the data” Free On-Line Dictionary of Computing
• •
•
“A collection of data arranged for ease and speed of search and retrieval by a computer. ” American Heritage Science Dictionary
•
Uses of Databases
• Library catalogues • Medical records • Bank accounts • Stock market data • Personnel systems • Product catalogues • Telephone directories
• Train timetables • Airline bookings • Credit card details • Student records • Customer histories • Stock market prices • Discussion boards • and many more...
Why Study Databases? • •
Almost everything we see on a computer uses a DBMS. Philosophy - the nature of reality that we are trying to model.
•
no entities, just statements of communicated fact.
•
relation rather than object oriented programming
•
This could well be the next trend in programming
•
MONEY and JOBS!
Why Study Databases? • Many computing applications deal with large amounts of information.
• Database systems give a set of tools for • •
storing, searching and managing this information. Databases are a ‘core topic’ in computer science and IT. Basic concepts and skills with database systems are part of the skill set you will be assumed to have as a CS and IT graduate.
File Based Systems • File based systems • Data is stored in files
• Each file has a
specific format
• Programs that use these files depend on knowledge about that format
•Problems: • No standards • Data duplication • Data dependence • No way to generate complex queries
• No provision for
concurrency, security, recovery, etc.
An Example • From the Manga Guide to Databases • The Kingdom of Kod exports apples • Price is 100G per container of apples • Departments: • Merchandise • Overseas Business • Export
An Example
An Example • From the Manga Guide to Databases • The Kingdom of Kod exports apples • Price is 100G per container of apples • Departments: • Merchandise • Overseas Business
An Example
• Mistakes get made, the overseas business department didn’t get the message...
• What if the price changes?
•
Redundant Data Storing the same data several times in different places (redundancy) is errorprone!
Database Systems •
A DATABASE is a system to allow multiple users to share the SAME information. Any item of data should only be stored once Any changes to this data is thus available to all users A Database Management System (DBMS) is the software that implements a database
• • •
• Oracle • DB2 • MySQL • Ingres
• PostgreSQL • Microsoft SQL Server • [MS Access]
What a DBMS Does •
•
Allows users to: store data manage change (updates) organise data retrieve data retain privacy (security) Provides: Data Definition Language (DDL) Data Manipulation Language (DML) Data Control Language (DCL) These may be the same language!
• • • • •
Where is the DBMS?
web pages HTML
custom client
AJAX
web server
DMBS tools
public API
DBMS (server)
• • • •
File System / OS
DBMS Components • Data dictionary • stores information about database objects • Data dictionary compiler • extracts database information and store it in data dictionary • Query processor • interprets and optimises user queries • Transaction manager • communicates with recovery manager and •
scheduler to ensure data consistency in multi-user environments Storage manager
ANSI / SPARC Architecture
Interaction of DBMS Components
User Query (via client)
Query Processor
Database Administrator
interp rets q uerie optim s izes q uerie s
Transaction Manager Storage Manager
concurrency control recovery control ent nagem
ce ma
a file sp
Database
•
DD Compiler
Data Dictionary
•
Proposed a framework for DBMS in 1975
• •
Standards Planning Requirements Committee
•
Internal level
American National Standards Institute
Three tier architecture
• •
•
for systems designers
•
for database designers
•
for database users
Conceptual level External level
Types of Database Users • • • •
Database systems programmers
•
writes the DBMS software
•
designs and manages the database system
•
write the client software that allows end users to interface with the DBMS
Conceptual Level • Deals with the organisation of the entire database content
• Abstractions are used to remove
Database administrators (DBA)
unnecessary details of the internal level
• Used by DBAs and application
Applications developers
End users
•
programmers
• Conceptual Schema: • For example:
CREATE TABLE Employee ( Name VARCHAR(25), Salary REAL, Department VARCHAR(10) )
use the information provided by the database to achieve a personal or organisational goal
External Level • Provides a view of the database tailored to
Internal Level •
a user
• Parts of the data may be hidden • Used by end users and application programmers
• External Schema: • For example:
Create View myView as { SELECT Name FROM Employee }
•
Deals with physical storage of data
• • •
Structure of records on disk - files, pages, blocks Indexes and ordering of records Used by database system programmers
Internal Schema:
•
For example: RECORD EMP LENGTH=44 HEADER: BYTE(5) OFFSET=0 NAME: BYTE(25) OFFSET=5 SALARY: FULLWORD OFFSET=30 DEPT: BYTE(10) OFFSET=34
