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Databases
MMG508
DB Properties
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Definition of a database:
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“A database is a collection of interrelated data
items that are managed as a single unit”
MS Access – all data is contained in a single
file
ORACLE – all data is contained in a
“collection” of physical files that are managed
by an instance of their database software
DB Properties (Cont’d)
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Some definitions
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Instance – a copy of the specific database
software running in memory
Definitions are very interesting – one term can
mean different things between two vendors
Database Object is “a named data structure that is
stored in a database”
Database Model is an organization methodology
that is designed to emulate the real world
DB Properties (Cont’d)
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Definitions (Cont’d)
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File – a collection of related records stored as a
single unit by an operating system
Using the term “File” for a database is
inappropriate because these files do not contain:
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Management by the DBMS
Layers of data abstraction
Physical data independence
Logical data independence
Four Major DB Properties
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First – The Database Management System
(DBMS)
Provides services to:
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Move data to and from physical files
Manage usage of concurrent data between various
users
Managing transactions
Support for a query language (SQL*Plus (Oracle),
MYSQL, SQL, PL/SQL (Oracle)
Four Major DB Properties (Cont’d)
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Procedures for Backup and Recovery of the
database
Security
Four Major DB Properties (Cont’d)
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Second - Layers of Data Abstraction
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Provision of User Views
The Physical Layer
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Data files that hold all the data for the database.
Most modern DBMS store the database in multiple
files
The Logical Layer
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This is the logical layout of the database
For the most part, looks like an organization chart
Four Major DB Properties (Cont’d)
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Layers of Data Abstraction (Cont’d)
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The External Layer
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This is where users and application programs that
access the database connect and issue queries against
the database.
Third - Physical Data Independence
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The ability to make changes to the physical file
structure without interrupting user actions
Four Major DB Properties (Cont’d)
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Fourth - Logical Data Independence
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The ability to make changes to the logical db
layer without disrupting existing users
Database Models
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Flat files
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The Hierarchical Model
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Files that are created and utilized by standard
computer operations (See p. 8)
This model was used in the first dbms’ (looks like
an organization chart) (See pp. 10-11)
The Network Model
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Similar to the hierarchical model
Database Models (Cont’d)
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Relational Model
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Developed by Dr. E.F. Codd
This was revolutionary work
Let’s look at Figures 1-7/1-8 on pp. 14/15
Object-Oriented Model
Object-Relational Model
Why Focus on RDBMS?
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As you text states:
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Definition, maintenance, and manipulation of data storage
structures is easy
Data is retrieved through simple ad hoc queries
Data is well protected
Well-established ANSI and ISO standards exist
There are many vendors from which to choose
Conversion between vendor implementations is relatively
easy
RDBMSs are mature and stable products
QUESTIONS????