Chapter 9 Databases Objectives In this chapter we will: Scrutinize ...

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Oct 31, 2013 (3 years and 9 months ago)

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Chapter 9


Databases


Objectives

In this chapter we will:

1.

Scrutinize the characteristics of a Database

2.

Study the features of a Database Management
System

3.

Look at the architectures of Database Management Systems

4.

Examine the evolution of Database Technology


Learning outcomes
:

At the end of the chapter, students will be able to:

1.

Identify the characteristics of a D
atabase

2.

Describe the f
eatures of
a
Database Management System

3.

Explain the various architectures of a Database Management System

4.

Discuss the e
volution of Database Technology


9.0

I
ntroduction


What is a database?

A database is a collection of information that is organized so that it can
easily be accessed, managed, and updated. We can have a database of any kind of content


bibliographic, full
-
text, numeric and images. We can even have a multimedia database.
A
dat
abase
is often abbreviated as DB
.
You can also think of a database as an electronic filing
system. Traditional databases are organized by fields, records, and files. A field is a single piece
of information; a record is one complete set of fields; and a fi
le is a collection of records. For
example, a telephone book is analogous to a file. It contains a list of records, each of which
consists of three fields: name, address, and telephone number.


With the advent of the Internet Technology, a new concept in database design has been
introduced, which is known as a Hypertext database. In a Hypertext database, any object,
whether it
is

a piece of text, a picture, or a film,
it
can be linked to any othe
r object. Hypertext
databases are particularly useful for organizing large amounts of disparate information, but
they are not designed for numerical analysis.


The size of a database can vary widely, from a few megabytes for personal databases, to
gigabyte
s (a gigabyte is 1000 megabytes) or even terabytes (a terabyte is 1000 gigabytes) for
large corporate databases. The information in a database is stored on a nonvolatile medium
that can accommodate large amounts of data; the most commonly used such media a
re
magnetic disks. Magnetic disks can store significantly larger amounts of data than main
memory, at much lower costs per unit of data.


Examples of the use of database systems include airline reservation systems, company payroll
and employee information
systems, banking systems, credit card processing systems, and sales
and order tracking systems
,
computerized library systems, automated teller machines, flight
reservation systems and computerized parts inventory systems
.

Let us look at an example
illustra
ted in Table 9.0


Table 9.0 contains details about each student. There are six pieces of information on each
student. They are Metric No, Name, Date of birth, Sex, Address and Courses. Each piece of
information in database is called a
Field
. We can define
field
as

the smallest unit in a database
.
Each field represents one and only one characteristic of an event or item. Thus there are six
fields in this database. If we were to take a close look at all these fields, we can see that they
are not of the same type. Date of birth is
date
type whereas
Name is
character

type. All the
related fields for a particular event is called a
Record
. In the example above, all six fields taken
together for a particular student is called a record of that student. Since there are six students
there are six records. T
hus, we can define record as
a collection of logically related fields
. We
can now say that
a database

is a collection of logically related records.




Table 9.0
: A Student Database

Metric
No.

Name

Date of
birth

Sex

Address

Courses

9721001

Maryam

21.05.1980

M

C36, Sector 2, Manama, Bahrai n

Pol Sc, Eco, Hi story, Eng,
Stati sti cs

9721002

Adi tya

12.06.1981

M

At/Po.
Orange Street, Dubai

Phy, Chem, Bi ol ogy, Eng,
Geol ogy

9732012



Rahul
Jai n

03.01.1979

F

A31, Pi l ani, Raj asthan
, I ndia

Pol

Sc, Eco, Hi story, Eng, Maths

9724004



Ahmad
Al i

23.11.1979

M

12A, Shei kh Sarai
-
I,
Dahran,
Saudi Arabi a

Phy, Chem, Bi ol ogy, Eng, I T

9715023



C. Suresh

07.09.1980

M

96, Mal vi ya Nagar,
Sri Lanka

Pol Sc, Eco, Hi story, Eng,
Programmi ng


9.2

Features of
Database Management Systems

The
next question is: How do we create and manage our databases?
Data management involves
creating, modifying, deleting and adding data in files, and using this data to generate reports or
answer queries. The software that allow
s us to perform these functions easily is called a
Data
Base Management System

(DBMS). Using a DBMS files can be retrieved easily and effectively.


There are many DBMS packages available in the market. Some of them are:



MySQL,



PostgreSQL,



Microsoft
Access,




SQL Server,



FileMaker,



Oracle,



RDBMS,



dBASE,



Clipper, and



FoxPro.


9.1

Database Characteristics

A database has several characteristics that make it useful
and irreplaceable
.


9.1.1 Concurrent Use

A database is always used by more than one user at the same time. In this case a
database

system allows several users to access the database concurrently. Answering different questions
from different users with the same (base) data is a central aspect of an information system.

Such concurrent use of data increases the economy of a system. Data

capturing and data
storage is not redundant, the system can be operated from a central control and the data can
be updated more efficient.

An example for concurrent use is the travel database of a bigger
travel agency. The employees of different branches

can access the database concurrently and
book journeys for their clients. Each travel agent sees on his
computer

if there are still seats
available for a specific journey or if it is already fully booked.

Figure 9.
1.
1 describes how
multiple users can sha
re the same database.


Figure 9.
1.
1
: A database enabling concurrent access

9.1.2

Structured

and Described Data

A database s
ystem does not only contain

data but also the complete definition and description
of these data.
A database contains metadata which describes the data itself
-

the structure, the
type and the format of all data and, additionally, the relationship between the data.
Metadata
is sometimes known as "data about data"
.



Structured Data
:

Data is called str
uctured if it can be subdivided systematically and linked.
Lets us look at an
example of how data can be structured. Table 9.1
.2

has four columns.

F
irst
column

= Prename, second column = Name, third column = Postcode, forth column = City

I
t is known that
a
n

entry in the first column must be a prename (coded as string) and an entry
in the third column must be a postcode (coded as number).


Table 9.1
.2
: A table of Names and Addresses

Firstname [string]

Familyname [string]

Postcode

City [string]

Rohit

Gupta

14000

Srinagar

Hanif

Salam

46350

Klang

….

…..

….

….


9.1.3

Separat
es
Data and Applications

When using a database,
the
application

software does not need
to know
about the physical
data storage like encoding, format, storage place, etc. It only communicates with the
management system of a database (DBMS) via a
standardized

interface with the help of a
standardized

language like SQL. The access to the data and the m
etadata is entirely done by the
DBMS.

In this way all the applications can be totally
separated

from the data. Therefore
database internal
reorganizations

or improvement of efficiency do not have any influence on
the application software.
Figure 9.
1.3

desc
ribes how this can be done.


Figure 9.1.3
:
Separating Data from Application Systems

9.1.4


Data Integrity

Data integrity
means
the quality and the reliability of the data of a database system.
D
ata
integrity includes also the protection of the database from
unauthorized

access (confidentiality)
and
unauthorized

changes
.
.Data reflect facts of the real world. Logically, it is demanded that
this reflection is done correctly. A DBMS should support th
e task to bring only correct and
consistent data into the database. Additionally, correct transactions ensure that the consistency
is maintained during the operation of the system. An example for inconsistency would be if
contradictory statements were save
d in the same database.

Student Record in the Library

Name

Address

Haziq Hamidi

No.11, Yellow Road,
Ipoh, Malaysia

Rami Mayan

No.22 Oxfam Road, Klang, Malaysia

Sunny Darwish

No. 134, Silk Road, Singapore

….

….


Student Record in the Accounts
Department

Name

Address

Haziq Hamidi

No.11, Yellow Road, Ipoh, Malaysia

Rami Mayan

No.22 Oxfam Road, Klang, Malaysia

Sunny Darwish

No. 74, Lime Tree Road, Norwich, UK

….

….


9.
1.
5
.
Data Persistence

Data persistence means that in a DBMS all data is maintained as long as it is not deleted
explicitly
. The life span of data needs to be determined directly or indirectly be the user and
must not be dependent on system features. Additionally data once store
d in a database must
not be lost.



9.1.6

Data Views

Typically, a database has several users and each of them, depending on access rights and
desire, needs an individual view of the data (content and form). Such a data view can consist of
a subset of the stored data or of from the stored data derived data (n
ot
explicitly

stored).
For
example:
A university manages the data about students. Beside matriculation number, name,
address, etc. other information like in which course the student is reg
istered, if he needs to do
a receipt
, and so on is managed as
well.
This

extensive database is used by several people all
with different needs and rights.

A student can view only his own data:
-

name address, contact
number, his courses, grades and fees paid. A lecturer can view only student metric number,
names and grades

of those students that he/she teaches. A Dean can only see all student,
lecturers and staff details if they are in his Faculty.


9.2

Features of Database Management Systems

A database management system (DBMS) is designed to manage a large body of inform
ation.
Data management involves both defining structures for storing information and providing
mechanisms for manipulating the information. In addition, the database system must provide
for the safety of the stored information, despite system crashes or at
tempts at unauthorized
access. If data are to be shared among several users, the system must avoid possible
inconsistent

results due to multiple users concurrently accessing the same data.



Accessing desired records from a large relation using a scan on t
he relation can be very
expensive. Indices are data structures that permit more efficient access of records. An index is
built on one or more attributes of a relation; such attributes constitute the search key. Given a
value for each of the search
-
key attr
ibutes, the index structure can be used to retrieve records
with the specified search
-
key values quickly. Indices may also support other operations, such as
fetching all records whose search
-
key values fall in a specified range of values.


A database schem
a is specified by a set of definitions expressed by a data
-
definition language.
The result of execution of data
-
definition language statements is a set of information stored in
a special file called a data dictionary. The data dictionary contains metadata,

that is, data about
data. This file is consulted before actual data are read or modified in the database system. The
data
-
definition language is also used to specify storage structures and access methods.


Data manipulation is the retrieval, insertion, de
letion, and modification of information stored in
the database. A data
-
manipulation language enables users to access or manipulate data as
organized by the appropriate data model. There are basically two types of data
-
manipulation
languages: Procedural dat
a
-
manipulation languages require a user to specify what data are
needed and how to get those data; nonprocedural data
-
manipulation languages require a user
to specify what data are needed without specifying how to get those data.


A query is a statement re
questing the retrieval of information. The portion of a data
-
manipulation language that involves information retrieval is called a query language. Although
technically incorrect, it is common practice to use the terms query language and data
-
manipulation l
anguage synonymously.


Database languages support both data
-
definition and data
-
manipulation functions. Although
many database languages have been proposed and implemented,
SQL

has become a standard
language supported by most relational database systems. Databases based on the object
-
oriented model also support declarative query languages that are similar to SQL.

SQL provides a
complete data
-
definition language, including the ab
ility to create relations with specified
attribute types, and the ability to define integrity constraints on the data.


Query By Example (QBE) is a graphical language for specifying queries. It is widely used in
personal database systems, since it is much
simpler than SQL for non
-
expert users.

Forms interfaces present a screen view that looks like a form, with fields to be filled in by users.
Some of the fields may be filled automatically by the forms system. Report writers permit
report formats to be defin
ed, along with queries to
fetch

data from the database; the results of
the queries are shown formatted in the report. These tools in effect provide a new language for
building database interfaces and are often referred to as fourth
-
generation languages (4G
Ls).


Often, several operations on the database form a single logical unit of work, called a
transaction. An example of a transaction is the transfer of funds from one account to another.
Transactions in databases mirror the corresponding transactions in t
he commercial world.

Traditionally database systems have been designed to support commercial data, consisting
mainly of structured
alphanumeric

data. In recent years, database systems have added support
for a number of nontraditional data types such as tex
t documents, images, and maps and other
spatial data. The goal is to make databases universal servers, which can store all types of data.
Rather than add support for all such data types into the core database, vendors offer add
-
on
packages that integrate w
ith the database to provide such functionality.


9.3

Architectures of Database Management Systems

The database architecture is the set of specifications, rules, and processes that dictate how data
is stored in a database and how data is accessed by compon
ents of a system. It includes data
types, relationships, and naming conventions. The database architecture describes the
organization of all database objects and how they work together. It affects integrity, reliability,
scalability, and performance. The d
atabase architecture involves anything that defines the
nature of the data, the structure of the data, or how the data flows.


The overall structure of the database is called the database schema. The schema specifies data,
data relationships, data semantic
s, and consistency constraints on the data. The entity
-
relationship data model is based on a collection of basic objects, called entities, and of
relationships among these objects. An entity is a “thing” or “object” in the real world that is
distinguishabl
e from other objects. For example, each person is an entity, and bank accounts
can be considered entities. Entities are described in a database by a set of attributes. For
example, the attributes account
-
number and balance describe one particular account i
n a bank.
A relationship is an association among several entities. For example, a depositor relationship
associates a customer with each of her accounts. The set of all entities of the same type and the
set of all relationships of the same type are termed
an entity set and a relationship set,
respectively.


Like the entity
-
relationship model, the object
-
oriented model is based on a collection of
objects. An object contains values stored in instance variables within the object. An object also
contains bodies

of code that operate on the object. These bodies of code are called methods.
The only way in which one object can access the data of another object is by invoking a method
of that other object. This action is called sending a message to the object. Thus,
the call
interface of the methods of an object defines that object's externally visible part. The internal
part of the object

the instance variables and method code

are not visible externally. The
result is two levels of data abstraction, which are importa
nt to abstract away (hide) internal
details of objects. Object
-
oriented data models also provide object references which can be
used to identify (refer to) objects.


In record
-
based models, the database is structured in fixed
-
format records of several type
s.
Each record has a fixed set of fields. The three most widely accepted record
-
based data models
are the relational, network, and
hierarchical

models. The latter two were widely used once, but
are of declining importance. The relational model is very wide
ly used. Databases based on the
relational model are called relational databases.


The relational model uses a collection of tables (called relations) to represent both data and the
relationships among those data. Each table has multiple columns, and each
column has a
unique name. Each row of the table is called a
tuple
, and each column represents the value of
an attribute of the tuple.


9.
4

Evolution of Database Technology

Ancient to modern
: The origins go back to libraries, governmental, business, and medical
records. There is a very long history of information storage, indexing, and retrieval.


1960's
: Computers become cost effective for private companies along with increasing storage
cap
ability of computers. Two main data models were developed: network model (CODASYL)
and hierarchical (IMS). Access to database is through low
-
level pointer operations linking
records. Storage details depended on the type of data to be stored. Thus adding an

extra field
to your database requires rewriting the underlying access/modification scheme. Emphasis was
on records to be processed, not overall structure of the system. A user would need to know the
physical structure of the database in order to query for

information. One major commercial
success was SABRE system from IBM and American Airlines.


1970
-
72
: E.F. Codd proposed relational model for databases in a landmark paper on how to
think about databases. He disconnects the schema (logical organization) of

a database from the
physical storage methods. This system has been standard ever since.


1970's
: Several camps of proponents argue about merits of these competing systems while the
theory of databases leads to mainstream research projects. Two main protot
ypes for relational
systems were developed during 1974
-
77. These provide nice example of how theory leads to
best practice.


Ingres: Developed at UCB. This ultimately led to Ingres Corp., Sybase, MS SQL Server, Britton
-
Lee, Wang's PACE. This system used QU
EL as query language.

System R: Developed at IBM San Jose and led to IBM's SQL/DS & DB2, Oracle, HP's Allbase,
Tandem's Non
-
Stop SQL. This system used SEQUEL as query language.

The term Relational Database Management System (RDBMS) is coined during this p
eriod.


1976
: P. Chen proposed the Entity
-
Relationship (ER) model for database design giving yet
another important insight into conceptual data models. Such higher level modeling allows the
designer to concentrate on the use of data instead of logical tab
le structure.


Early 1980's
: Commercialization of relational systems begins as a boom in computer purchasing
fuels DB market for business.


Mid
-
1980's
: SQL (Structured Query Language) becomes "intergalactic standard". DB2 becomes
IBM's flagship product.
Network and hierarchical models fade into the background, with
essentially no development of these systems today but some legacy systems are still in use.
Development of the IBM PC gives rise to many DB companies and products such as RIM, RBASE
5000, PARAD
OX, OS/2 Database Manager, Dbase III, IV (later Foxbase, even later Visual FoxPro),
Watcom SQL.


Early 1990's
: An industry shakeout begins with fewer surviving companies offering increasingly
complex products at higher prices. Much development during this

period centers on client tools
for application development such as PowerBuilder (Sybase), Oracle Developer, VB (Microsoft),
etc. Client
-
server model for computing becomes the norm for future business decisions.
Development of personal productivity tools s
uch as Excel/Access (MS) and ODBC. This also
marks the beginning of Object Database Management Systems (ODBMS) prototypes.


Mid
-
1990's
: The usable Internet/WWW appears. A mad scramble ensues to allow remote
access to computer systems with legacy data. Cli
ent
-
server frenzy reaches the desktop of
average users with little patience for complexity while Web/DB grows exponentially.


Late
-
1990's
: The large investment in Internet companies fuels tools market boom for
Web/Internet/DB connectors. Active Server Pages, Front Page, Java Servlets, JDBC, Enterprise
Java Beans, ColdFusion, Dream Weaver, Oracle Developer 2000, etc are examples of such
offe
rings. Open source solution come online with widespread use of gcc, cgi, Apache, MySQL,
etc. Online Transaction processing (OLTP) and online analytic processing (OLAP) comes of age
with many merchants using point
-
of
-
sale (POS) technology on a daily basis.


Early 21st century
: Decline of the Internet industry as a whole but solid growth of DB
applications continues. More interactive applications appear with use of PDAs, POS
transactions, consolidation of vendors, etc. Three main (western) companies predomin
ate in
the large DB market: IBM (buys Informix), Microsoft, and Oracle.


Future trends
: Huge (terabyte) systems are appearing and will require novel means of handling
and analyzing data. Large science databases such as genome project, geological, national

security, and space exploration data. Data mining, data warehousing, data marts are a
commonly used technique today. More of this in the future without a doubt.
Smart/personalized shopping using purchase history, time of day, etc.


Successors to SQL (and perhaps RDBMS) will be emerging in the future. Most attempts to
standardize SQL successors
have

not been successful. SQL92, SQL2, SQL3 are still
underpowered and more extensions are hard to agree upon. Most likely this will be overta
ken
by XML and other emerging techniques. XML with Java for databases is the current poster c
hild
of the "next great thing".


Mobile database use is a product now coming to market in various ways. Distributed
transaction processing is becoming the norm for

business planning in many arenas. Probably
there will be a continuing shakeout in the RDBMS market. Linux with Apache supporting mySQL
(or even Oracle) on relatively cheap hardware is a major threat to high cost legacy systems of
Oracle and DB2.


Object
Oriented Everything, including databases, seems to be always on the verge to sweeping
everything before it. Object Database Management Group (ODMG) standards are proposed and
accepted and maybe something comes from that.


Ethical/security/use issues tend
to be diminished at times but always come back. Should you be
able to consult a database of the medical records/genetic makeup of a prospective employee?
Should you be able to screen a prospective partner/lover for genetic diseases? Should
amazon.com keep
track of your book purchasing? Should there be a national database of
convicted sex offenders/violent criminals/drug traffickers? Who is allowed to do Web tracking?
How many times in the last six months did you visit a particular sex chat room/porn
site/po
litical satire site? Who should be able to keep or view such data? Who makes these
decisions?



Summary

A database is a collection of information that is organized so that it can easily be accessed,
managed, and updated.
The software that allows us to perform these functions easily is called a
Data Base Management System

(DBMS). Using a DBMS files can be retrieved easily and
effectively.
A database has several characteristics that make it useful and irreplaceable. It
enabl
es concurrent use; it can describe and structure data, separate data from application,
ensures data integrity, data persistence, and provide multiple data views.


The database architecture is the set of specifications, rules, and processes that dictate ho
w data
is stored in a database and how data is accessed by components of a system. It includes data
types, relationships, and naming conventions.
The origins go back to libraries, governmental,
business, and medical records. There is a very long history of

information storage, indexing, and
retrieval. Future trend of database will be focused on mobile database usage. Data mining, data
warehousing, data marts are a commonly used technique in the future.



Exercise:

True or False

1.

The relational model uses a c
ollection of tables (called relations) to represent both data and
the relationships among
st data files
.

2.

The entity
-
relationship model and

the object
-
oriented model
are

based on a collection of
objects.

3.

The database
design
is the set of specifications,
rules, and processes that dictate how data
is stored in a database and how data is accessed by components of a system.

4.

A database management system (DBMS) is designed to manage a large body of
records
.

5.

Query By

Example (QBE) is a graphical language for specifying queries. It is widely used in
personal database systems, since it is much simpler than SQL for non
-
expert users.

6.

A

data view can consist of a subset of the stored data or from the stored data derived da
ta (not
explicitly stored).

7.

A database contains metadata which describes the data itself
.

8.

The size of a database can
only be
from a few megabytes for personal databases, to
gigabytes (a gigabyte is 1000 megabytes) for large corporate databases.

9.

Answering d
ifferent questions from different users with the same (base) data is a central
aspect of

a database
.

10.

A record is
a collection of logically related fields
.


Answers:

1.

False

2.

True

3.

False

4.

False

5.

True

6.

True

7.

True

8.

False

9.

False

10.

True


Short
Essay questions:

1.

Define field, record, file, and database briefly.

2.

Name three DBMS packages.

3.

What are the benefits of using a database in an information system?

4.

What are the features of a DBMS?

5.

Describe briefly the evolution of the database.