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HSQ - DATABASES & SQL
05 Concepts of DBMS
By MANSHA NAWAZ
Section 05
Concepts Of DBMS
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Introduction
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In this lecture we will be looking at some of the fundamental concepts
behind a Database Management System (DBMS).
– RDBMS - Relational DBMS
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Exploring the Advantages and Disadvantages of using a DBMS
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Exploring the Architecture of a DBMS and some of the associated issues.
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Advantages of the DBMS Approach
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The Database Approach Versus the Traditional File Processing Approach
– Storing data in a non-redundant database improves consistency of data.
• There is only one copy of each item of data.
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Unproductive Maintenance avoided.
– In file based systems, changes to file structure cause endless problems on
maintenance (re-writing code).
– Using a DBMS, program access is through a limited view (using SQL).
• Thus programs can’t see minor changes to the database.
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We will be exploring data independence in more detail later .
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Some of the Advantages of using a DBMS
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Sharing of data
Control of redundancy and thus Data consistency
Improved data integrity
Better data accessibility
Representing complex relationships among data
Enforcing integrity constraints
Better security of data (as long as backup is perfect)
More control over concurrency
Better backup and recovery procedures
Providing multiple interfaces
Faster development of new applications
Economy of scale
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Some of the Disadvantages of using a DBMS
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High cost of Software
Hardware costs high due to software complexity
Requirement for skilled staff
Higher programming costs - greater skill required
Slower processing of some applications
Increased vulnerability (all your eggs in one basket)
More difficult recovery (if disaster strikes)
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DBMS Architecture
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Usually taken to imply a three level architecture.
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The complexity of a large database is handled by a DBMS by providing three
views of the data.
– An internal view of how the data is stored and accessed
– A conceptual view of what data is available in the database.
– Local or external views which are a limited and simplified view of the
database as suitable for a single application or group of associated
applications.
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Data abstraction
– Users deal with conceptual representation of the data.
– They have little control over how the data is stored.
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Three Level Architecture
External
Level
View
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View
2
View
3
Logical Data
Independence
Conceptual Level
Conceptual Schema
View
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et
c.
ERD - Logical View
Physical Data
Independence
Internal Level
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Internal Schema
ERD - Table View
One of the fundamental aspects of the database approach using a DBMS
is that, by providing levels of data abstraction, it hides complexity of data
storage from users.
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Database schema - the description of a database
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Schema - a description of a database in terms that a DBMS understands
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External Schema
– A database system may have several external schemas each suitable for a
single application or group of associated applications.
– They provide a means of limiting the perceived complexity of a large system.
– Hide those parts of the database which are not required for a particular
purpose or department (useful security).
– External schemas are based on the conceptual schema.
– Each external schema describes a section of the database of interest to a
particular group of users (or programs).
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Client/Server Architecture
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Server provides services for the Clients which are responsible for interacting with
the users (Input/Output)
Server is responsible for performing a service (e.g. transaction) and guaranteeing
the integrity of the data
Well suited for distributed systems handling large amounts of data
User Workstation
Department
File-Servers
Corporate
Servers
User Workstation
Operator
Workstation
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Database Development
Systems Analysis & Design
DFD DataStores, DataFlows and Data Dictionary
DATA MODEL
TABLE SET
E-R Model
NF
DBMS
PHYSICAL VIEW OF DATA
LOGICAL VIEW OF DATA
TABLES
FORMS
Database connectivity via
websites
www .net technology
Macromedia Dreamweaver
MS Visual Studio
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Database connectivity via
desktop DBMS such as
MS Access
Concepts Of DBMS
Database connectivity
via programming
languages such as MS
Visual Basic
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Area of Interest
End of Lecture
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