Database Management System

1.1 Introduction1.1 Introduction
Traditional database applications
New applications: multimedia databases,
geographic information system,
data warehouses, …
Database: A collection of related data.
Data: Known facts that can be recorded and have an
implicit meaning.
(e.g., names, telephone numbers, addresses, …)
(indexed address book, diskette, …)
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1-2
Database Management System(DBMS): A software
package to facilitate the creation and maintenance of a
computerized database.
˙Defining ˙Constructing ˙Manipulating
Database System: The DBMS software together with the
data itself.
Mini-world (Universe of Discourse): Some part of the real
world about which data is stored in a database. For example,
student grades and transcripts at a university.
• Library card catalog: generated & maintained manually
• Computerized database

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1-5a
Define UNIVERSITY databaseDefine UNIVERSITY database
Structure of the record
STUDENT ( Name , Number, Class, Major)
COURSE ( Name , Number, Credit, Dept.)
Data type of data element
Name: a string of characters
Number: integer
Grade: {A,B,C,D,F,I}
…..
Constraints
The sections that students take must be taught by some instructors.

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1-5b
Construct UNIVERSITY databaseConstruct UNIVERSITY database
Store data on storage medium
˙store data for each student, course, section, grade repot, prerequisite
˙records in various files may be related to one another
Manipulate UNIVERSITY databaseManipulate UNIVERSITY database
Query:
Retrieve the transcript ( a list of all courses and grades) of Smith.
Update:
Create a new section for the database course for this semester.

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Figure 1.1 A simplified database system environment

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1.2 An Example1.2 An Example
Mini-world for the example: Part of a UNIVERSITY environment.
Some mini-world entities:
- STUDENTs
- COURSEs
- SECTIONs (of COURSEs)
- (academic) DEPARTMENTs
- INSTRUCTORs
Some mini-world relationships:
- SECTIONs are of specific COURSEs
- STUDENTs take SECTIONs
- COURSEs have prerequisite COURSEs
- INSTRUCTORs teach SECTIONs
- COURSEs are offered by DEPARTMENTs
- STUDENTs major in DEPARTMENTs

7
Entity-Relationship Model
 A logical representation of the data for an organization
or for a business area
 3 constructs:
 Entity - person, place, object, event, concept (often
corresponds to a row in a table)
 Attribute - property or characteristic of an entity (often
corresponds to a field in a table)
 Relationship – link between entities (corresponds to primary
key-foreign key equivalencies in related tables)
 Type vs. instance
• Entity type: Instructor
• Entity instance: Leon Chen
 Entity-Relationship Diagram
 A graphical representation of entity-relationship model
 Also called E-R diagram or just ERD
STUDENT
Name
Registers

8
Sample E-R Diagram (Figure 3-1)
Supplier_ID
Supplier_Name
Supplier_Address
Attribute

9
Relationship
degrees specify
number of entity
types involved
Entity
symbols
A special entity
that is also a
relationship
Relationship
symbols
Relationship
cardinalities
specify how
many of each
Attribute
symbols

10
Entity
 Person: EMPLOYEE, STUDENT
 Place: WAREHOUSE, COUNTRY
 Object: BUILDING, MACHINE
 Event: SALE, REGISTRATION
 Concept: ACCOUNT, COURSE
EMPLOYEE DEPENDENT
Strong entity Weak entity
Associative entity
CERTIFICATE

11
What Should an Entity Be?
 SHOULD BE:
 An object that will have many instances in
the database
 An object that will be composed of multiple
attributes
 An object that we are trying to model
 SHOULD NOT BE:
 A user of the database system
 An output of the database system (e.g. a
report)

12
Inappropriate entities
System userSystem user System outputSystem output
Appropriate entities
Figure 3-4

13
Attribute
 Attribute - property or characteristic of an
entity type
 Classifications of attributes:
 Required vs. Optional Attributes
 Simple vs. Composite Attribute
 Single-Valued vs. Multivalued Attribute
 Stored vs. Derived Attributes
 Identifier Attributes - keys

14
Required vs. Optional Attributes
 Example: entity – ONLINE_ACCOUNT
 Required attributes (Not NULL)
• Account_ID
• Password
• Owner_Name
 Optional attributes
• Phone_Number
• Password_Hint

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Figure 3-7 – A composite attribute
An attribute
broken into
component parts

16
Figure 3-8 – Entity with a multivalued attribute (Skill) and
derived attribute (Years_Employed)
Derived
from date employed and current date
Multivalued:
an employee can have
more than one skill

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Figure 3-19 – An attribute that is both multivalued and composite
This is an example of
time-stamping.
More examples?

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Identifiers (Keys)
 Identifier (Key) - An attribute (or
combination of attributes) that uniquely
identifies individual instances of an entity
type
 Candidate Key – an attribute that could be
a key. Examples (for STUDENT,
PERSON)?
 Simple Key versus Composite Key

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Figure 3-9a Simple key attribute
The key is underlined

20
Figure 3-9b Composite key attribute
Flight_Number Date

21
Guidelines for Identifiers
 Will not change in value
 Will not be null
 Substitute new, simple keys for long,
composite keys
 ?  Game_Number

22
Relationship
 Relationship Type vs. Relationship
Instance
 Degree of a relationship
 Cardinality of a relationship
 Associative Entity – combination of
relationship and entity

23
Figure 3-11a
The relationship type is modeled as the
diamond and lines between entity types
attribute of the relationship

24
Relationship Instance is between
specific entity instances

25
One entity
related to
another of
the same
entity type
Entities of
two different
types related
to each other Entities of three
different types
related to each
other
Degree of a relationship is the number
of entity types that participate in it

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Cardinality of a Relationship
 One-to-One
 Each entity in the relationship will have exactly one
related entity
 One-to-Many
 An entity on one side of the relationship can have
many related entities, but an entity on the other side
will have a maximum of one related entity
 Many-to-Many
 Entities on both sides of the relationship can have
many related entities on the other side

29
Note: a relationship can have attributes of its own

30
Cardinality Constraints
 Cardinality Constraints - the number of instances
of one entity that can or must be associated with
each instance of another entity
 Minimum Cardinality. Examples?
 If zero, then optional
 If one or more, then mandatory
 Maximum Cardinality. Examples?
 The maximum number

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Cardinalities
Mandatory one
Mandatory many
Optional one
Optional many
11
18

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Figure 3-16a Basic relationship
Mandatory minimum cardinalities – Figure 3-17a

33
Figure 3-17c
Optional cardinalities with unary degree, one-to-one relationship

34
max cardinality
constraint
Maximum Cardinality Constraint

35
Entities can be related to one another in more than one way

36
Attributes can be transformed to relationships
Attributes or Relationship?

37
Attributes should be transformed to relationships
Attributes or Relationship?

38
Associative Entities

It’s an entity – it has attributes

AND it’s a relationship – it links entities together
 When should a relationship with attributes be an
associative entity?
 All relationships for the associative entity should be many
 The associative entity could have meaning independent of the
other entities
 The associative entity should have at least one or more
attributes other than the identifier
 The associative entity may participate in other relationships
other than the entities of the associated relationship
 Ternary relationships should be converted to associative
entities

39Figure 3-11b – An associative entity (CERTIFICATE)

40
Bill of materials structure

41
Figure 3-18 – Ternary relationship as an associative entity

42
Strong vs. Weak Entities
 Strong entities
 exist independently of other types of entities
 has its own unique identifier
 represented with single-line rectangle
 Weak entity
 dependent on a strong entity…cannot exist on its own
 does not have a unique identifier
 represented with double-line rectangle
 Identifying relationship
 links strong entities to weak entities
 represented with double line diamond

43
Strong entity Weak entityIdentifying relationship

44
Figure 3-22a
E-R diagram for Pine
Valley Furniture

45
Microsoft Visio
Notation for Pine
Valley Furniture
Different modeling
software tools may
have different
notation for the
same constructs

46
Relationship
degrees specify
number of entity
types involved
Entity
symbols
A special entity
that is also a
relationship
Relationship symbols
Relationship
cardinalities
specify how
many of each
Attribute symbols

47
Sample E-R Diagram (Figure 3-1)
Supplier_ID
Supplier_Name
Supplier_Address
Attribute

48
E-R Diagram for a
Banking Enterprise

Library Case Study
 When a library first receives a book from a publisher it is sent,
together with the accompanying delivery note, to the library desk.
Here the delivery note is checked against a file of books ordered.
 If no order can be found to match the note, a letter of enquiry is sent
to the publishers. If a matching order is found, a catalogue note is
prepared from the details on the validated delivery note.
 The catalogue note, together with the book, is sent to the
registration department. The validated delivery note is sent to the
accounts department where it is stored.
 On receipt of an invoice from the publisher, the accounts
department checks its store of delivery notes. If the corresponding
delivery note is found then an instruction to pay the publishers is
made, and subsequently a cheque is sent. If no corresponding
delivery note is found, the invoice is stored in a pending file.

A Case Study
Conference centre booking system
A conference centre takes bookings from clients who wish to hold courses or conferences at the
centre. When clients make bookings they specify how many people are included in the booking,
and of these, how many will be resident during the booking, and how many will require catered or
non-catered accommodation at the centre.
The centre contains a number of facilities which may be required by clients making bookings as
follows:
A. There are 400 bedrooms for clients who will be resident during the Course or
conference.
B. A maximum of 250 catered people can be handled at any one time.
C. Six main lecture theatres providing seating for 200 people.
D. Twenty seminar rooms each able to accommodate 25 people.
E. Video conference facilities. The video conference facilities consist of four separate
video conference networks. Each video conference network has a large screen based
in one of the main lecture theatres, along with 3 satellite screens each of which is
based in one of the seminar rooms.
Draw an entity relationship diagram for the case, stating any assumptions you deem necessary.

Shipping company example
 The London and Ireland Shipping Company PLC (LISC) was founded in 1852 and owns a fleet of cargo ships.
The company had historically run passenger liners, but recent policy decisions involved the sale of all passenger-
carrying vessels. The company currently has 14 vessels, including one oil tanker and one tugboat operating out of
Liverpool. Most of the vessels are registered in Liberia for tax reasons.
 Each ship has one or more holds divided into spaces. The holds are defined by steel bulkheads and the spaces
are defined by shelf racks or other physical dividers. Sister ships, built by the same shipbuilders and to the same
designs have similar names, such as Pride of Ireland, Queen of Ireland, Song of Ireland and Warrior of Ireland.
Sister ships also have identical cargo storage facilities.
 LISC issues contracts to agents for one or more manifests (lists of cargo items to be shipped). LISC's charges for
cargo carried are based on the number of spaces the cargo requires for storage. The types of cargo typically
carried by LISC include grain, coal and ores (carried only in ships equipped with bulk cargo holds). They also
transport sacked grain, heavy cases, containers (which may be carried on deck), pallets and so on.
 Cargo items may take up less than one space in a hold, or one or more spaces, depending on the size of the
item. A space may therefore contain several small cargo items.
 The ships owned by LISC are kept as busy and as full as possible, in order to maximise the profits that each
vessel makes and minimise running & operating costs. LISC's ships ply most of the seas of the world, but tend to
operate mainly in the Mediterranean, the North and Mid Atlantic and the Indian Ocean. Different ships require
different crew complements.
 LISC intends to create a computer based information system that will be able to perform the following tasks:
 • record the voyages of each ship with the start and end ports.
 • record the cargo held by a ship on each voyage
 • keep records of their employees and the ships they are assigned to
 • producing invoices for agents and customers
 • keep a record of customers' payments on invoices
 • analyse the efficiency of use of cargo space and of percentage wasted cargo space for ships voyages

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1.3 Characteristics of the Database Approach1.3 Characteristics of the Database Approach
• File Processing
Each user defines and implements the files needed for a specific application
Redundancy in defining & storing data
• Database Approach
A single repository of data
-Self-describing nature of a database system: A DBMS catalog stores the
description of the database. The description is called meta-data . This allows the
DBMS software to work with different databases.
catalog: structure of each file, type & storage format of each data item, constraints on
data
-Insulation between programs and data: Called program-data independence.
Allows changing data storage structures without having to change the DBMS access
programs.(see 1-7)
program–
Interface + method
operation independence (OODB)

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1.6 Advantages of Using a DBMs1.6 Advantages of Using a DBMs
1.6.1 Controlling Redundancy in data storage and in development and
maintenance efforts.
duplication efforts waste space inconsistent‧ ‧ ‧
( see 1-12 controlled redundancy)
1.6.2 Restricting Unauthorized Access (security and authorization)
1.6.3 Providing Persistent Storage for Program Objects and Data
Structures.
1.6.4 Permitting Inferencing and Actions Using Rules
1.6.5 Providing Multiple User Interfaces
1.6.6 Representing Complex Relationships Among data.
1.6.7 Enforcing Integrity Constraints
1.6.8 Providing Backup and Recovery

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-Potential for Enforcing Standards.
-Reduced Application Development Time.
-Flexibility.
-Availability of Up-to-date Information.
-Economies of Scale.
1.7 Implications of the1.7 Implications of the DatabaseDatabase ApproachApproach

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1.8 When not to use a DBMS1.8 When not to use a DBMS
Main costs of using a DBMS:
- High initial investment in hardware, software,training
and possible need for additional hardware.
- Overhead for providing generality, security, recovery, integrity, and
concurrency control.
- Generality that a DBMS provides for defining and processing data.
When a DBMS may be unnecessary:
- If the database and applications are simple, well defined, and not
expected to change.
- If there are stringent real-time requirements that may not be met
because of DBMS overhead.
- If access to data by multiple users is not required.

Summary
In today’s session we have learned
to:
Identify the entities
Determine the attributes for each entity
Select the primary key for each entity
Establish the relationships between the
entities
Draw an entity model

Database Management System

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Database Management System