Network Database Management Systems (Essay Sample)

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Network Database Management Systems
A Network database management system
uses a data model similar to Hierarchical
database management systems The major
difference here is that the tree structure in
the Network models can have a many parent
to many child relational model. The Network
model structure is based on records and sets
and most of these databases use SQL for
manipulation of their data.
Network database management systems tend
to be very flexible but are rarely used ad were
very quite common in the1960s and 1970s.
Searching for an item in this model requires
the program to traverse the entire data set
which is quite cumbersome. These have
mainly been replaced by Relational database
management systems in today's modern
computing.
Object-oriented Database Management
Systems
Object-oriented database management
systems borrow from the model of the Object-
oriented programming paradigm. In this
database model, the Object and its data or
attributes are seen as one ad accessed
through pointers rather than stored in
relational table models. Object-oriented
database models consist of diverse structures
and is quite extensible.
This data model was designed to work closely
with programs built with Object-oriented
programming languages thereby almost
making the data and the program operate as
one. With this model, applications can treat
the data as native code. There is little
commercial implementation of this database
model as it is still developing. Examples of
Object-oriented database management
systems include IBM DB4o and DTS/S1 from
Obsidian Dynamics.
References
Source:
1. John H. Porter Research Associate
Professor, Department of Environmental
Sciences, University of Virginia.1......Relational Database Management Systems
Relational database management systems are
the most widely used database management
systems today. They are relatively easy to
use. Relational database management
systems are named so because of the
characteristic of normalizing the data which is
usually stored in tables. The relational model
relies on normalizing data within rows and
columns in tables.
The data can be related to other data in the
same table or other tables which have to be
correctly managed by joining one or more
tables. Relational models may be somewhat
less efficient than other models; however, this
may not be a problem with the processing
power and memory found in modern
computers.
Data in this type of model is stored in fixed
predefined structures and are usually
manipulated using Structured Query Language
(SQL). Relational database management
systems include Oracle, Ms SQLServer, IBM
DB2, MySQL, SQLite and PostgreSQL among
others. Here is a code example of SQL in
operation on a relational database
management system
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Flat File Based Database Management.2......Database models continue to evolve as the
information management needs of organizations
become more complex. From flat files to
relational databases, the growing demands on
data integrity, reliability and performance of
database management systems (DBMS), has
shaped the design of databases and their
underlying models. In this document, three
database models are discussed comparing and
contrasting their major features. The three
models in order of discussion are Hierarchical,
Network and Relational database models.
Hierarchical Database Model
The hierarchical model is the oldest of the
three models discussed here. This model is an
improvement of the flat-file database system
since it employs a simple data relationship
scheme. The relationships in the hierarchical
model are child/parent relationships. The name
“hierarchical” is derived from one major
restriction on the child/parent relationships, that
is, although a parent entity can have several
child entities, a child entity can only have one
and only one parent. For this reason all the
relationships form a hierarchy that traces back
to one root. In fact, this model is often
visualized as an upside down tree, where the
entity at the top is seen as a root and as such
all other entities sprout from the root. A simple
example is shown in Figure 1 below
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Comparison of the Hierarchical, Network, and
Relational, Database Models
“Products” in Figure 1 above is the root entity of
the hierarchical model in the example.
As shown in the diagram, one major problem
with the hierarchical model is the increased risk
of data inconsistency. In the case above, a
separate “Customers” table must exist for every
product line due to the fact that a child entity
cannot have more than one parent. However,
there is a great chance that there are many
customers who purchased more than one type
of product. Consequently, information about
those customers must exist in more than one
table causing data redundancy. Another problem
with the hierarchical model is the inflexibility of
the model. For example, in the diagram above,
the database is restricted to three product
lines. Adding a new product line would require
redesigning the database since all the
relationships must be predefined. Finally,
another problem with the hierarchical model is
in the child/parent relationship restriction. Every
child must have a parent. Therefore, in the
example above, it is impossible to add new
customers who have not bought any new
products yet. To overcome some of the
limitations of the hierarchical model, the
network model was created.
Network Database Model
The network model is an improvement to its
predecessor, the hierarchical model. In the
network model, a child entity can have more
than one parent. Therefore, the design can be
visualized as several inverted trees
interconnected by branches as opposed to the
single inverted tree characteristic of the
hierarchical model. Figure below illustrates the
network database model of the hierarchical
database discussed previously.
As shown above, the network database model
eliminates the need to maintain several
“Customers” tables. Data in the network model
can be accessed from an entity as opposed to
the hierarchical model that requires access
from the root entity. The relationships between
entities occur through unique set structures.
Therefore, although the entities are not
duplicated, a unique set structure is required to
facilitate each of the one-to-many relationships.
Like the hierarchical model, the network model
is also navigational. This poses a big problem in
complex designs since the user has to
understand the database structure in order to
us the database. Furthermore, with a predefined
structure like in the hierarchical model,
modifying the structure of the database
becomes a difficult task. The relational model
eliminates many of the problems presented in
the network and hierarchical models.
Relational Database Model
The relational model is based on the
mathematical set theory. In this model, “data is
stored in relations which are perceived by the
user as relations” (Hernandez, 17). Relations
are made up of tuples (also referred to as
records or rows) and attributes (also known as
fields or columns). Each record is identified by
a column with a unique value. The order of the
rows and columns is of importance. Therefore,
the relational model is independent of physical
implementation, a quality that makes this model
more preferable to the hierarchical and
database models. Relationships in this model
can be one-to-one, one-to-many, or many-to-
many. Regardless of the type of relationship,
the model is transparent to the user, that is, the
user does not need to understand the physical
structure of the database in order to use it.
Relational databases also have their share of
problems. The flexibility of the relational model
comes with the price of performance speed
since the relationships are not predefined like in
the case of hierarchical and network databases.