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Database management systems (initiation)
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Presentation
Examples
Characteristics Data independence
• Physical independence
• Logical independence
Data models • Hierarchical model
• Network model
• Relational model
• Object-oriented model
Data architecture • External level
• Logical level
• Internal level
Database management systems is a
software package that allows users to
create, edit, query, update and administrate
Database
it also defines rules to validate and
manipulate this data.
Using DBMS final users can simply store
modify extract information from database.
Characteristics
Data independence is a form of database
management that keeps data separated
from all programs that make use of it.
Data cannot be redefined or reorganized by
any of the programs that make use of it. In
this manner, the data remains accessible,
but it is also stable and cannot be corrupted
by the applications
It is the ability to change the internal
schema(Using new storage media, Using
different data structures, switching from one
access method to another, using different file
organizations or storage structures, modifying
indexes, ...) for reasons of optimization or
reorganization without affecting the
application programs.
Logical data independence makes it
possible to change the structure of the
data(addition or deletion of fresh entities,
attributes or relationships... )
independently of modifying the
applications or programs that make use
of the data.
It’s a collection of concepts, rules and
tools for the description of the structure
of the database.
Structure of the database means the
data types, the data semantics, the
constraints and the relationships for the
description or storage of data
respectively.
The hierarchical data
model organizes data in
a tree structure
each entity has only one
parent but can have
several children . At the
top of hierarchy there is
only one entity which is
called Root.
In the network model,
entities are organized in
a graph, in which some
entities can be accessed
through several path
The network model
organizes data in a tree
structure but allows each
record to have multiple
parent and child records
A relational database
allows the definition of
data structures, storage
and retrieval operations
and integrity constraints.
the data and relations
between them are
organized in tables.
A table is a collection of
records and each record in
a table contains the same
fields.
Object-oriented models
define a database as a
collection of objects
with features and
methods.
information is
represented in the
form of objects as used
in object-oriented
programming
Models, policies, rules or standards that
govern which data is collected, and how it is
stored, arranged, integrated, and put to use in
data systems and in organizations
The architecture of a database system
determines its capability, reliability,
effectiveness and efficiency in meeting user
requirements.
A database management system provides
three views of the database data:
The highest level of
abstraction it define and
specify user views : views
that enable different data
users to see it in different
ways
It also contains the method
of deriving the objects in
the external view from the
objects in the conceptual
view.
The next-higher level of
abstraction describes what
data are stored in the
database, and what
relationships exist among
those data.
It defines how information
is arranged within the
database.
the conceptual schema
describes all relations that
are stored in the database
The lowest level of
abstraction
It describes how the data will
be physically stored and
accessed, using a DBMS.
So it describes details of how
data is stored: files, indices,
etc. on the random access
disk system.
It also typically describes the
record layout of files and type
of files
