Database systems - Chapter 1

CSC271 Database Systems
Lecture # 1

Chapter 1 - Objectives
 Some common uses of database systems
 Characteristics of file-based systems
 Problems with file-based approach
 Meaning of the term database (DB)
 Meaning of the term Database
Management System (DBMS)

Chapter 1 - Objectives
 Typical functions of a DBMS.
 Major components of the DBMS
environment.
 Personnel involved in the DBMS
environment.
 History of the development of DBMSs.
 Advantages and disadvantages of DBMSs.

Examples of Database
Applications
 Purchases from the supermarket
 Purchases using your credit card
 Booking a holiday at the travel agents
 Using the local library
 Taking out insurance
 Renting a video
 Using the Internet
 Studying at university

File-Based Systems
 Early attempt to Computerize the manual
filing system
 Collection of application programs that
perform services for the end users (e.g.
reports).
 Each program defines and manages its
own data.

Manual Filing Systems
 Works well
while number of items to be stored is small
For only storage or retrieval functionality of
large number of items

File-Based Systems
 Consider DreamHome example for file-
based systems
Sales Department : responsible for selling
and renting of properties
Contract Department: responsible for
handling lease agreements

Sales Department
 PropertyForRent
(propertyNo, street, city, postcode, type, rooms, rent,
ownerNo)
 Client
(clientNo, fName, lName, telNo, preftype, maxRent)
 PrivateOwner
(ownerNo, fName, lName, address, telNo)

ownerNo fName lName address telNo
CO46 Joe Keogh … 01224-861212
CO87 Carol Farrel … 0141-357-7419
CO40 … … … …
CO93 … … … …
propertyNo street city postcode type rooms rent ownerNo
PA14 … Aberdeen … House 6 650 CO46
PL94 … London … Flat 4 400 CO87
PG4 … Glasgow … Flat 3 350 CO40
PG21 … Glasgow … House 5 600 CO87
PrivateOwner
PropertyForRent

clientNo fName lName telNo prefType maxRent
CR76 John Kay 0207-774-5632 Flat 425
CR56 Aline Stewart 0141-848-1825 Flat 350
CR74 Mike Ritchie 01475-392178 House 750
CR62 Mary Tregear 01224-196720 Flat 600
Client

Contract Department
 Lease
(leaseNo, propertyNo, clientNo, rent , paymentMethod,
deposit, paid, rentStart, rentFinish, duration)
 PropertyForRent
(propertyNo, street, city, postcode, type, rooms, rent)
 Client
(clientNo, fName, lName, telNo, preftype, maxRent)

Lease
leaseNo propertyNo clientNo rent --- rentStart rentFinish duration
10024 PA14 CR62 650 1-Jun-05 31-May-06 12
… … … … … … … …
propertyNo street city postcode type rooms rent
PA14 … Aberdeen … House 6 650
PL94 … London … Flat 4 400
PG4 … Glasgow … Flat 3 350
PG21 … Glasgow … House 5 600
PropertyForRent

clientNo fName lName telNo
CR76 John Kay 0207-774-5632
CR56 Aline Stewart 0141-848-1825
CR74 Mike Ritchie 01475-392178
CR62 Mary Tregear 01224-196720
Client

Limitations of File-Based
Approach
 Separation and isolation of data
 Each program maintains its own set of data.
 Users of one program may be unaware of potentially
useful data held by other programs.
 For example, if we want to produce a list of all houses
that match the requirements of the clients.
 Duplication of data
 Decentralized approach taken by each department.
 Same data is held by different programs.
 Wasted space and potentially different values and/or
different formats for the same item.

Limitations of File-Based
Approach..
 Data dependence
 File structure is defined in the program code.
 Incompatible file formats
 Programs are written in different languages, and so cannot
easily access each other’s files.
 Fixed Queries/Proliferation of application
programs
 Programs are written to satisfy particular functions.
 Any new requirement needs a new program.

Database Approach
 Arose because:
 Definition of data was embedded in application programs,
rather than being stored separately and independently.
 No control over access and manipulation of data beyond
that imposed by application programs.
 Result:
 the database and Database Management System (DBMS).

Database
 Shared collection of logically related data,
and a description of this data, designed to
meet the information needs of an
organization.
 System catalog (metadata) provides
description of data to enable program-
data independence.
 Logically related data comprises entities,
attributes, and relationships of an
organization’s information.

Database Management
System (DBMS)
 A software system that enables users to
define, create, maintain, and control
access to the database.
 (Database) application program: a
computer program that interacts with
database by issuing an appropriate
request (SQL statement) to the DBMS.

Database Management
System (DBMS)..

Database Approach
 Data definition language (DDL).
 Permits specification of data types, structures and any data
constraints.
 All specifications are stored in the database.
 Data manipulation language (DML).
 General enquiry facility (query language) of the data.

Database Approach..
 Controlled access to database may include
 A security system
 Which prevents unauthorized users accessing the database
 An integrity system
 Which maintains the consistency of stored data
 A concurrency control system
 Which allows shared access of the database
 A recovery control system
 Which restores the database to a previous consistent state in case of
hardware or software failure
 A user-accessible catalog
 Which contains description of the data in the database

Views
 Allows each user to have his or her own
view of the database.
 A view is essentially some subset of the
database.

Views - Benefits
 Reduce complexity
 Provide a level of security
 Provide a mechanism to customize the
appearance of the database
 Present a consistent, unchanging picture
of the structure of the database, even if
the underlying database is changed

Summary
 Introduction to DB and DBMS
 File-based systems and their limitations
 Database approach

Components of DBMS
Environment

Components of DBMS
Environment..
 Hardware
 Can range from a PC to a network of computers.
 Software
 DBMS, operating system, network software (if
necessary) and also the application programs.
 Data
Used by the organization and a description
of this data called the schema.

Components of DBMS
Environment..
 Procedures
 Instructions and rules that should be applied to the
design and use of the database and DBMS.
 People

Roles in the Database
Environment
 Data Administrator (DA)
 Database planning
 Development and maintenance of standards, policies and procedures
 Database Administrator (DBA)
 Physical realization of the database
 Physical database design and implementation
 Security and integrity control
 Maintenance of the operational system
 Ensuring satisfactory performance of the applications for users
 Database Designers (Logical and Physical)
 Application Programmers
 End Users (naive and sophisticated)

History of Database
Systems
 Roots of the DBMS
Apollo moon-landing project, 1960s
NAA (North American Aviation), prime
contractor for the project
Developed a software GUAM (Generalized
Update Access Method), hierarchical
In mid – 1960s IBM joined NAA, result was
IMS(Information Management System)

History of Database
Systems..
 IDS ( Integrated Data Store)
By General Electric, network, mid-1960
 CODASYL ( Conference on Data Systems
Languages)
 DBTG (Data Base Task Group)

History of Database
Systems..
 DBTG proposal in 1971, components
The network schema: the logical
organization of the entire database as seen
by the DBA – which includes a deﬁnition of
the database name, the type of each record,
and the components of each record type.
The subschema: the part of the database as
seen by the user or application program;
A data management language to deﬁne the
data characteristics and the data structure,
and to manipulate the data.

History of Database
Systems..
 DBTG specified three languages
A schema Data Definition Language (DDL),
which enables the DBA to define the schema.
A subschema DDL, which allows the
application programs to define the parts of
the database they require.
A Data Manipulation Language (DML), to
manipulate the data.

History of Database
Systems..
 E. F. Codd, 1970
IBM Research Laboratory
Relational model
System R project by IBM’S San Jose
Research Laboratory California
Result of this project
 Development of SQL
 Commercial relational DBMS products e.g. DB2,
SQL/DS from IBM, Oracle from Oracle Corp.

DBMS Generations
 First-generation
 Hierarchical and Network
 Second generation
 Relational
 Third generation
 Object-Relational
 Object-Oriented

Advantages of DBMSs
 Control of data redundancy
 Data consistency
 More information from the same amount of
data
 Sharing of data
 Improved data integrity (constraints)
 Improved security (authentication, rights)
 Enforcement of standards (data formats,
naming conventions, documentation etc.)

Advantages of DBMSs..
 Economy of scale (economical cost)
 Balance conflicting requirements
 Improved data accessibility and
responsiveness (ad hoc queries)
 Increased productivity (developer)
 Improved maintenance through data
independence
 Increased concurrency

Advantages of DBMSs..
 Improved backup and recovery services

Disadvantages of DBMSs
 Complexity
 Size (disk space for DBMS)
 Cost of DBMS
 Additional hardware costs
 Cost of conversion
 Performance
 Higher impact of a failure

Summary
 Introduction to DB and DBMS
 File-based systems and their limitations
 Database approach
 Components of the DBMS environment
 Roles in the DB environment
 History of DBMS
 Advantages/Disadvantages of DBMSs

Database systems - Chapter 1

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Database systems - Chapter 1