Database Management System
Lecture 3
Models of Database Management
Systems
Learning Outcome
• Compare and contrast the structure of different
database management systems
• Define hierarchical databases
• Define network databases
• Define relational databases
• Define object-oriented databases
List of Topic
Hierarchical Databases
• The hierarchical data model organizes data in a
tree structure (as shown in the Figure) which
includes parents and child data segments.
Hierarchical Databases (Cont.)
• Hierarchical databases were introduced by
IBM in the 1960s with the introduction of
their IMS DBMS and were popular until the
1970s
• It is one of the oldest methods of organizing
and storing data
Hierarchical Databases (Cont.)
• A hierarchical database is organized in
pyramid fashion, like the branches of a tree
extending downwards
• Related fields or records are grouped together
so that there are higher-level records and
lower-level records
Network Databases Model
Network Databases Model (Cont)
• The network data model was formally defined
in 1971 at the Conference on Data Systems
Languages (CODASYL).
• It is a modified version of the hierarchical
model described with the one-to-many parentchild relationship constraint relaxed allowing
many-to-many relationships in data
Network Databases Model (Cont)
• a network database looks more like a cobweb
or interconnected network of records
• child or member can have more than one
parent (or owner).
First Generation DBMS: Network and
Hierarchical
• Required complex programs for even
simple queries.
Minimal data independence
Relational Data Model
Relational Data Model (Cont.)
• The most widely used data model in DBMSs
• It was developed by E. F. Codd at IBM in
1970.
• Data in a relational data model is organised in
tables.
• Each table is composed of a collection of
records.
Relational Data Model (Cont.)
• Each record contains a set of fields.
• Tables in a database can have relationships
between them.
• Each row in a table is unique with no two rows
or more having the same values in all its fields
Relational Data Model (Cont.)
Relational Data Model (Cont.)
• Tuple / Row
• A single row in the table is called as tuple. Each
row represents the data of a single entity.
• Attribute / Column
• A column stores an attribute of the entity. For
example, if details of students are stored then
student name is an attribute; course is another
attribute and so on.
Relational Data Model (Cont.)
• Column Name
• Each column in the table is given a name. This
name is used to refer to value in the column
• Table Name
•
Each table is given a name. This is used to refer
to the table. The name depicts the content of the
table
Object-oriented Databases
(OODBMS)
Object-oriented Databases
(OODBMS) (Cont.)
• An OODBMS is the result of combining object
oriented programming principles with database
management principles.
.
Object-oriented Databases
(OODBMS) (Cont.)
• One-to-one mapping between object-oriented
programming objects and database objects is
achieved in OODBs.
• Thus, less overhead can be achieved when
storing and retrieving database objects by
object-oriented applications
Object-oriented Databases
(OODBMS) (Cont.)
• able to handle many new data types, including
graphics, photographs, audio, and video
• an object-oriented database can be used to
store data from a variety of media sources,
such as photographs and text, and produce
work, as output, in a multimedia format.
Object-oriented Databases
(OODBMS) (Cont.)
• Object-oriented databases use small, reusable
chunks of software called objects
• The objects themselves are stored in the
object-oriented database
Object-oriented Databases
(OODBMS) (Cont.)
• Each object consists of two elements:
1)
a piece of data (e.g., sound, video, text, or
graphics)
2)
the instructions, or software programs
called methods, for what to do with the data
Object-oriented Databases
(OODBMS) (Cont.)
• The instructions contained within the object
are used to do something with the data in the
object
• For example, test scores would be within the
object as would the instructions for calculating
average test score
Object-oriented Databases
(OODBMS) (Cont.)
• Object-oriented databases have two
disadvantages
1) they are more costly to develop
2)
most organizations are reluctant to
abandon or convert from those databases that
they have already invested money in
developing and implementing
Object-oriented Databases
(OODBMS) (Cont.)
• benefits to object-oriented databases are
• The ability to mix and match reusable objects
provides incredible multimedia capability
• Healthcare organizations, for example, can
store, track, and recall CAT scans, X-rays,
electrocardiograms and many other forms of
crucial data.
Summary
• In this lesson, the following topics were
discussed:
• Compare and contrast the structure of different
database management systems.
• Define hierarchical databases.
• Define network databases.
• Define relational databases.
• Define object-oriented databases.