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What is a Database System?
What is a Database System?
Lecture 1
1
What is a Database System?
Informal introduction
 what do you think a database system is?
 think of some (real life) examples of
database systems
 main features provided by a database system
 store (insert, delete and update) and retrieve data
2
What is a Database System?
Example: part of a relational database
Title
Band
Genre
Location
Price Stock
Closing Time
Tom Waits
pop
ShaCow29
14.99
22
Golden
Saxophone
The best of John
Williams
Unplugged
Mozart - Cosi
Fan Tutte
collection
atmosphere
CaCk00
2.99
3
John Williams
classic guitar
MA10
10.49
15
Eric Clapton
collection
blues
classic
VP111
ME01
14.99
1.99
7
24
3
What is a Database System?
Database / file-based system
 definition
 … is a software (computer program, system) that
provides assistance in the management of data
 approaches
 decentralised  file based system
 centralised  database system
4
What is a Database System?
File-based system : Sales Dept’s files
Sales Department files
Property for rent file
PropertyId
Street
Area
City
PostCode
Type
NoOfRooms
Rent
OwnerId
Owner file
OwnerId
FirstName
LastName
Address
TelNo
Address
TelNo
Renter file
RenterId
FirstName
LastName
PreferredType
MaxRent
5
What is a Database System?
File-based system : Contracts Dept’s files
Contracts Department files
Property for rent file
PropertyId
Street
Area
City
PostCode
Rent
Renter file
RenterId
FirstName
LastName
Address
TelNo
Address
TelNo
Owner file
OwnerId
FirstName
LastName
Lease file
LeaseID
PropertyId RenterId OwnerId Rent TypeOfPayment
Deposit
Start
Finish
6
What is a Database System?
The file-based approach
group 1 of users
Application 1
Files of
Application 1
group 2 of users
Application 2
Files of
Application 2
group n of users
Application n
Files of
Application n
7
What is a Database System?
File based systems - limitations
 duplication of data
• wasteful
• prone to inconsistencies
 separation and isolation of data
• data cannot be used together
• incompatible file formats
 program-data dependence
• incompatible file formats
• fixed queries
8
What is a Database System?
Database / database system
 definition
• a database (DB) is a shared collection of logically related
persistent data as part of the information system of an
organisation
 main points
• persistent data
• logically related data
• shared
 database system
• database + the operations defined on it
9
What is a Database System?
The database approach
group 1 of users
Application 1
DBMS
DB
group 2 of users
Application 2
DB
raw data
+
data dict.
group n of users
Application n
10
What is a Database System?
Database management system
 definition
• a database management system (DBMS) is a software
that provides a set of primitives for defining, accessing
and manipulating data
11
What is a Database System?
Summary
 real life examples of database systems
 file-based systems
 database systems
 database (DB)
 database system
 database management system (DBMS)
12
What is a Database System?
Activity A1
Think of a real life system for data management developed in a
file-based approach (i.e. a system that you have or might have
come across). What disadvantages do you identify? Could any
of them be solved by adopting a database approach? Does the
database approach solution introduce any disadvantages?
13