IT 3002
Database Management
Systems
Introduction to Database Systems
Dhananjaya Perera
Senior Software Engineer
IFS R&D International
Why use a Database?
• Many people collect things
– How about you?
• If you collect anything, you probably are familiar with some of the
problems of managing a collection
– Ex: stamps, photos, paper cuttings
• One way to keep track of a collection is to create a database
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Data, Information and Knowledge
• Data
– Raw values relating to facts, events or transactions
– Raw facts and figures that on their own have no meaning, and used to generate information
– Ex: 00500
• Information
– Data that has been processed within a context to give it meaning
• Data which has meaning and context
– Ex: 00500 Postal code of Thimbirigasyaya
• Knowledge
– Use of information in context, to make decisions or come to a conclusion
– Knowledge is the understanding of rules needed to interpret information
– Facts, feelings or experience known by a person or group
– Ex: Manager could use the information to decide whether or not to raise or lower price
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File Based System
• Collection of application programs that perform services for the users
wishing to access information.
• File based systems were developed as better alternatives to paperbased filing systems
• Each program within a file-based system defines and manages its own
data
• In the business…
• It was common practice for larger companies to have each of its departments
looking after its own data
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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.
• Duplication of data
–Same data is held by different programs.
–Wasted space and potentially different values and/or different formats
for the same item.
• Dependence of data
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Limitations of File-Based Approach Cont…
• Incompatible file formats
– Programs are written in different languages, and so cannot easily access
each other’s files.
• Fixed queries of application programs
– Fixed queries of application programs
– Programs are written to satisfy particular functions.
– Any new requirement needs a new program.
• Increased number of different application programs
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Terminology for Intro…
• Database: A collection of related data.
• Data: Known facts that can be recorded and have an implicit meaning.
• Mini-world: Some part of the real world about which data is stored in
a database. For example, student grades and transcripts at a
university.
• Database Management System (DBMS): A software package/system
to facilitate the creation and maintenance of a computerized
database.
• Database System: The DBMS software together with the data itself.
Sometimes, the applications are also included.
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What is a Database?
• A database is an organized collection of data that are related in a
meaningful way and stored in a common pool which can be accessed
by one or many persons for many purposes.
• A database is a group of related files.
• Ex: UNIVERSITY database for maintaining information concerning
students, courses, and grades in a university environment.
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Database Management System (DBMS)
• DBMS is a software system that enables users to define, create, and
maintain the computerized database and that provides controlled
access to that database.
• DBMS is a general-purpose software system that facilitates the
processes of defining, constructing, manipulating, and sharing
databases among various users and applications.
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DBMS Functions
DATA Dictionary
Management
Data Storage
Management
Database Access
Languages and
Application Programming
Interfaces
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Data Integrity
Management
Security Management
DBMS
Presentation and
Visualization of data
Multiuser Access
Control
Backup and Recovery
Management
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Database System
• The DBMS software together with the data itself. Sometimes, the
applications are also included.
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High level architecture
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Characteristics of Database System
• 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.
• Insulation between programs and data:
• Called program-data independence. Allows changing data storage structures
and operations without having to change the DBMS access programs.
• Data Abstraction:
• A data model is used to hide storage details and present the users with a
conceptual view of the database.
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Characteristics Cont…
• Support of multiple views of the data:
• Each user may see a
different view of the database, which describes only
the data of interest to that user
• Sharing of data and multiuser transaction processing :
• allowing a set of concurrent users to retrieve and to update the database.
Concurrency control within the DBMS guarantees that each transaction is
correctly executed or completely aborted.
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Common Database Systems
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Major components of Database System
• Data
– The data in the database; integrated and shared
• Hardware
– Physically stores data, it can be secondary storage on which the database
physically resides together with associated I/O devices
• Software
– Between the physical database and the users is a layer of software which
is known as the DBMS
• Users
– Database Administrators
– Database Designers
– End Users
– System Analysts and Application Programmers (Software Engineers)
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Advantages over file-based system
• Minimal Data Redundancy
• Data files are integrated into a single, logical structure. Each primary fact is
recorded (ideally) in only one place in the database.
• Improved Data Consistency
• By eliminating (or controlling) data redundancy, we greatly reduce the
opportunities for inconsistency.
• Improved Data Sharing
• A database is designed as a shared corporate resource and can be shared by
all authorized users. In this way more users share more of the data.
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Advantages Cont…
• Enforcement of Standards
• When the database approach is implemented with full management support,
the database administration function should be granted single-point authority
and responsibility for establishing and enforcing data standards.
• Standards include naming conventions, data quality standards and uniform
procedures for accessing, updating and protecting data.
• Improved Data Integrity
• Integrity can be expressed in terms of constraints, which are consistency rules
that the database is not permitted to violate.
• Increased Concurrency
• Many DBMSs allow users to undertake simultaneous operations on the
database. The DBMS implements a concurrency control mechanism that
prevents database accesses from interfering with one another.
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Advantages Cont…
• Improved Data Accessibility and Responsiveness
• With relational database, end users without programming experience can
often retrieve and display data, even when it crosses traditional departmental
boundaries.
• English-like query language SQL and query tools such as Query-By-Example
provide such facilities.
• Improved Security
• DBMS can be used to enforce database security. This may take the form of
usernames and passwords to identify people authorized to use the database.
• The access that the authorized user is allowed on the data can also be
restricted by the operation type (retrieval, delete, update, insert).
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Disadvantages
• Complexity
• Size
• Cost of DBMS
• Additional hardware cost
• Cost of conversions
• Performance
• Higher impact of failure
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Database Building Blocks
• File/Entity/Table
– A collection of related records
• Record
– A record is a group of related fields
• Field/Attribute
– Field represents an attribute, or a characteristic, or a piece of
information
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Database Building Blocks Cont…
Database
Table
Table
Table
Record
Record
Record
Attributes
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Database Users
• Database Administrators (DBA)
– Administering resources (Database, DBMS and related software)
– Responsible for authorizing access to the database
– Coordinating and monitoring database’s (its) use
– Acquiring software and hardware resources as needed
– Accountable for problems such as breach of security or poor system response
time
• Database Designers
– Identify the data to be stored in the database
– Choose appropriate structures to represent and store this data
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Database Users Cont…
• Application Programmers
– Who develop the programs (Software Engineers)
• End Users
– database primarily exists for their use
– people whose jobs require access to the database for querying, updating, and
generating reports
– Categories
•
•
•
•
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Casual end users
Naive end users
Sophisticated end users
Stand-alone users
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Database Users Cont…
• Casual end users
– occasionally access the database
– may need different information each time
– use a query language to specify their requests
• Naive end users
– constantly querying and updating the database
– use standard types of queries and updates
– need to know very little about the DBMS
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Database Users Cont…
• Sophisticated end users
– thoroughly familiarize themselves with the facilities of the DBMS
– implement their applications to meet their complex requirements
• Stand-alone users
– maintain personal databases
– use ready-made program packages that provide easy-to-use menu-based or
graphics-based interfaces
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Meta Data
• Data that describe the properties or characteristics of other data.
• Some of these properties include the name of the data item, data
type, length, minimum and maximum allowable values (where
appropriate),rules or constraints and a brief description of each data
item.
• Meta data allow database designers and users to understand what
data exist, what the data mean.
• Data without clear meaning can be confusing, misinterpreted or
erroneous.
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Example for Meta data
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Analyzing the Scenario…
• Mini World : Part of a university environment
• Some mini world entities :
•
•
•
•
•
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STUDENTs
COURSEs
SECTIONs (of COURCEs)
(academic) DEPARTMENTs
INSTRUCTORs
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Cont…
• Some mini-world relationships:
•
•
•
•
•
•
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SECTIONs are of specific COURSEs
STUDENTs take SECTIONs
COURSEs have prerequisite COURSEs
INSTRUCTORs teach SECTIONs
COURSEs are offered by DEPARTMENTs
STUDENTs major in DEPARTMENTs
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Entities
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Usage
• Queries :
•
•
•
Retrieve the transcript—a list of all courses and grades—of ‘Smith’
List the names of students who took the section of the ‘Database’ course
offered in fall and their grades in that section
List the prerequisites of the ‘Database’ course
• Updates
•
•
•
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Change the class of ‘Smith’ to 2
Create a new section for the ‘Database’ course for this semester
Enter a grade of ‘A’ for ‘Smith’ in the ‘Database’ section of last semester
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