1. Databases
Cutajar & Cutajar

2. Conventional File Approach
 Each section keeps a separate file for storing information
 Example: Attendance and Results files
STUDENT ATTENDANCE INFORMATION
Surname Name ID Address Father Class ABSENT
Zammit John 217787M 7 Main Street, Zebbug Charles IT7B 23
Cutajar Mary 323187G 9 St. Martin Street, Zejtun George IT4C 1
Piscopo Natalie 787887M 9, B. Zammit Street, Attard Peter II2F 78
Duplication of data
STUDENT RESULTS INFORMATION
Surname Name ID Address Class Subject Mark
Zammit John 217787M 7 Main Street, Zebbug IT7B English 45
Cutajar Mary 323187G 9 St. Martin Street, Zejtun IT4C Maths 90
Piscopo Natalie 787887M 9, B. Zammit Street, Attard II2F Korean 12
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3. Problems in Conventional File
Systems
 The computer-based subsystems, being self-contained, do not
represent the way in which organizations really work
 Systems communicate with each other outside the computer
 Possibly data inconsistencies
 Data duplication
 Data non-shareable
 Overall view of company to help decision-making process is
almost next to impossible because of the large amount of work
involved. Information from different departments has to be
collated before appropriate statistics could be obtained - much
duplication of data is likely, creating unnecessary maintenance,
risk of inconsistencies and wastage of storage space.
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4. Example
 Consider a customer order
ORDER
Customer order Invoice
 PROCESSING 
(input) (output)
SYSTEM
(debtor’s
Customer control)
SALES ACCOUNTING
(debtor)   Statements &
SYSTEM
data confirmation
of payments
Required stock PURCHASING
  Stock order
(lacking) SYSTEM
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5. Integrated File Systems
 To overcome some of the problems with conventional file systems,
integrated file systems are employed. Here, the data is pooled into a
set of interlocking and interdependent files, which are accessible by a
number of different users (and applications).
E.g.:
User File A
1 Stock file
E.g.:
User Process File B
2 Order file
User File C
3
… …
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6. Problems with integrated file
systems.
 When a transaction enters the system, ALL the
appropriate files are updated.
 Most integrated file systems in use are usually tailor-
made to meet the requirements of particular
organizations.
 Data duplication problem still remains
 The task of maintaining the data is shared between
the programs that access and maintain the data and
therefore lacks proper central control.
 Programs are still dependant on the nature of the
data stored and vice-versa.
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7. DataBase Management
System
 Databases represent a radically different approach to
solving the problems discussed.
 Definition: A DATABASE is a single organized collection of
structured data stored with a minimum of duplication of data
items so as to provide a consistent and controlled pool of
data. This data is common to all users of the system, but is
independent of the programs that use it.
 (Alternative definition: A DATABASE is collection of non-
redundant data shareable between different application
systems)
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8. DBMS
 It is essentially a computerized record-keeping
system.
D
USER 1
B
PROCESS
USER 2 DATABASE
M
S
USER 3
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9. Database Access
 Note that, the DBMS is the only medium through which
any user may access the data in the database.
USER 1 DBMS USER
4
USER
5
USER 2
DataBase
USER 3
Here it is assumed that the data is contained in a single database. In practice there is often reason for the
data to be split across several distinct databases.
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10. Computer System
 Database management systems are available on machines
ranging from small microcomputers to the largest mainframes.
The facilities provided are to some extent determined by the size
and power of the underlying machine.
 On large machines one would usually find a multi-user system.
 On small microcomputers it is more usual to have a single user
database system.
Single-User System Multi-User System
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11. Hardware Requirements
 With regards to hardware requirements, databases demand
large secondary storage facilities, and other demands depending
on the circumstances.
 Direct access storage e.g. disc
packs, and so on.
 On-line storage i.e. computer
can access a given record without
human intervention
 In a multi-user system, users can
access the database at the same time
 For distributed databases, a fast,
reliable communications network
would be a requirement. Distributed System
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12. Database Environment
 In a Database Environment there are three classes of
users:
Application Programmer
Responsible for writing programs that use the
database
End User
May access database via an application program
Database Administrator (DBA)
Has central responsibility of the system.
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13. Application Programmer
 Responsible for writing programs that use the
database (by issuing appropriate requests to the
DBMS)
 Batch applications – on-line applications
 Function of programs is to support an end user
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14. End User
 May access database via an application program or
use the interface provided as an integral part of the
system by which the user is able to issue high level
commands to the DBMS.
 Typical functions include:
 Data Entry
 Issue of Reports
 Queries
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15. Database Administrator
(DBA)
 The DBA has central responsibility of the system.
 Co-ordinates database design
 Loads the database
 Controls access to the database (ensures
privacy and security)
 Establishes backup and recovery procedures
 Controls changes to the database
 Selects and maintains database
management software
 Meets the users to resolve problems and
determine changing requirements
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16. Advantages of Databases vs
Traditional Methods
 Compactness : no need for voluminous paper files
 Speed : the machine can retrieve and change
data much faster than any human
 Less drudgery : much of the sheer tedium of
maintaining files by hand is eliminated
 Currency : accurate up-to-date information is
available on demand at any time.
 Faster and cheaper development of new
applications
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17. In case of a multi-user
environment
 The database system provides the enterprise with centralized control of its
data
 Redundancy can be reduced (more usually controlled rather than totally
eliminated
 Inconsistency can be avoided
 Data can be shared
 Standards can be enforced: to enable data interchange; standards may
include corporate, installation, industrial, national, international
 Security restrictions can be applied: ensuring access to database through
proper channels; provision of security checks on access
 Integrity can be maintained: ensuring that the data in the database is
accurate
 Conflicting requirements can be balanced: provide overall service that is
‘best for the enterprise’
 Provision of data independence i.e. if application programs are revised,
these changes do not effect the database itself and vice-versa.
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18. Disadvantages of databases
vs traditional methods
 High initial investment in hardware, software and
training
 Generality that a DBMS provides for defining and
processing data
 Overhead for providing security, concurrency control,
recovery, and integrity functions
 (additional problems may arise if the database
designers and DBA do not properly design the
database or if the database systems applications are
not implemented properly)
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19. The Database
Management System
The database management system
(DBMS) is a complex software system
(system software), which constructs,
expands and maintains the
database.
Main objective of DBMS
 The DBMS handles all requests from
the users for access to the database
hence shielding users from hardware
level details.
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20. Functions of a DBMS
 Allocates storage to data
 Maintains indices so that any required data can be retrieved, allowing for
separate items of data in the base can be cross-referenced
 Maintains data in the database by providing facilities for adding new
records, deleting records, amending records and adding new sets of
records (data files)
 Provides an interface with user programs: Programmer need not be
familiar with the structure of the database, and write programs in different
programming languages
 File processing facilities: Process a complete file (serial/sequential),
process required records (selective sequential/random) and retrieve
individual records
 Provides security of data: Protects data against unauthorized access,
corruption and providing recovery and restart facilities after a hardware or
software failure
 Keeps statistics of the use made of the data, allowing redundant data to
be removed and Frequently used data to be kept in the most accessible
form
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21. Data Modeling
 In designing a database for an enterprise, initially one has to
identify and state what data needs to be stored – the data
requirements.
 Example: Stock control application-
 Each stock item has a stock number, a description, price, quantity in
stock, reorder level and supplier
 Each item has only one supplier
 From this statement of data requirements a conceptual data model is
produced.
OPERATIONAL DATA = ENTITIES + RELATIONSHIPS
E.g. suppliers E.g. suppliers supplies a certain kind
of part – hence link between supplier
and part entities
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22. The Conceptual Data Model
 A conceptual data model describes how the data elements in the
system are to be grouped. Three terms are used in building a picture
of the data requirements.
 An entity is a thing of interest to an organization about which data is to
be stored. - Example: stock, supplier, 
 An attribute is a property or characteristic of an entity. - Example: stock
item description
 A relationship is a link or association between entities.- Example: link
between stock items and suppliers: - one supplier may supply many
stock items
 This conceptual/logical model is created without any regard to what
type of database system will eventually be used to implement it.
Example: the entity stock and its attributes are expressed as follows:
STOCK(part_number, description, price, quantity, reorder level, supplier)
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23. Types of Relationships
 Each relationship has a name (e.g. supplies) and a
degree, which may be any of:
 one-to-one
 one-to-many (or many-to-one)
 many-to-many
 Example :- the relationship between supplier and stock:
 Name : supplies (as indicated)
 Degree: one-to-many
(a supplier supplies many stock items)
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24. Other Examples
 E.g. 1: One-to-one: a specialist is assigned to a single ward
(Given that a specialist has one ward of patients under his care)
 E.g. 2: One-to-many: a hospital ward occupied by many
patients (but a patient is assigned to only one ward).
 E.g. 3: Many-to-many: a student may study several courses,
each course has many students enrolled on it.
 Exercise: Identify the relationship between these entities:
 stock item and supplier
 CD and song
 Borrower and book
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25. Entity-Relationship Diagrams
(E-R Diagrams)
 An entity-relationship diagram is
a diagrammatic way of SPECIALIST WARD
representing the relationships
between the entities in a
database. To show the is occupied
relationship between two by
WARD PATIENTS
entities, both the degree and
the name of the relationship
need to be specified.
 An E-R diagram illustrates the studies
entities and their relationships STUDENT COURSE
for a specific system.
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26. Example 1
 The data requirements for a hospital in-patient system are defined
as follows:
 A hospital is organized into a number of wards. Each ward has a ward
number and a name recorded, along with a number of beds in that
ward. Each ward is staffed by nurses. Nurses have their staff number
and name recorded, and are assigned to a single ward.
 Each patient in the hospital has a patient identification number, and
their name, address and date of birth are recorded. Each patient is
under the care of a single consultant and is assigned to a single ward.
Each consultant is responsible for a number of patients. Consultants
have their staff number, name and specialisation recorded.
 (i) State four entities for the hospital in-patient system and suggest
an identifier for each of these entities.
 (ii) Draw an entity-relationship diagram to show the relationship
between the entities.
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27. Solution 1
ENTITY NAME
Ward Ward Number
Nurse Staff Number
Patient Patient Identification Number
Consultant Staff Number
staffed by holds visits
NURSE WARD PATIENT CONSULTANT
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28. Example 2
 In a mail order system, a customer may place an
order for several items. Over a period of time, the same
customer may place several orders.
 Drawing an E-R CUSTOMER ORDER
diagram to All the
represent this ORDER ITEM relationship
pairs
situation:
CUSTOMER ITEM
sends receives
CUSTOMER
is for
ORDER ITEM
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