Network relational model is no longer a major

Network Data Model

A database model that uses pointer-based data retrieval and
supports network data structures. (Augsten and Bo?hlen, n.d.) 

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Hierarchical data model

A database model that uses pointer-based data retrieval and
supports only Hierarchical data structure. (Augsten and Bo?hlen, n.d.) 

Relational Data Model

The relational database model emerged in the 1970s and
became prevalent during the 1980s. It uses the repetition of unique identifying
information to link related data. This method is somewhat slower and less
machine efficient than pointer-based retrieval. However, changes in the
structure of a database can be accommodated relatively easily under the
relational model. In addition, the relational model has a strong theoretical
basis, rooted in a few relatively simple principles.

standard language called structured query language (SQL) has emerged for
retrieval and processing of relational databases. SQL is a query language that
makes it relatively easy for end-users to access a database and retrieve
selected data to answer ad-hoc questions.

relational model is by far the most prevalent model in use today. Due to continuing
increases in the capacity and processing speed of computers, the slower data
recovery of the relational model is no longer a major disadvantage for most
systems.  (Hernandez, 2013)

At the
same time the flexibility and ease of use of the relational model have become more
and more important over time. The relational model was initially used primarily
for low- to medium-volume databases. It opened up the ability to apply database
technology to support individuals and work groups.

database technology can now provide suitable processing power even for many
high-volume databases. Hierarchical and network databases have been relegated
largely to the role of legacy systems- technologies that are no longer viable
for use in new systems. but are embedded in important ongoing systems that must
be maintained.

the scope of some of the systems developed under the hierarchical and network
models, and the cost involved in replacing them, it is likely that databases
based on the hierarchical and network models will continue to be used well into
the next century in recent years, the object-oriented data model has emerged.
Object-oriented concepts were first incorporated in object-oriented programming

In object-oriented systems. methods or procedures that can
be performed on data are stored, along with the data, in objects.
Object-oriented systems also emphasize the idea that objects inherit
characteristics from higher level classes of objects to which they belong.
Incorporating these concepts into database systems adds to the power of the
systems. but also adds to their complexity. Although databases incorporating
the concepts of the object-oriented model are commercially available, thus far.

Object-oriented databases have been implemented primarily
in engineering rather than business-oriented systems. Because the relational
model is most commonly used for business systems developed today.
(Silberschatz, Korth and Sudarshan, 2011) 



Data Representation in Database system


Metadata is an Information describing the nature and
structure of an organization`s data; data about data. (Elmasri and Navathe, n.d.)
Before we can begin to build a data model of a system, we must understand the
types of logical relationships or structures that can exist among physical
elements and that must be represented in our data models. This type of
information is commonly referred to as metadata. Metadata encompasses all
information about the structure of data, and restrictions on the values and
structures that data can have it is “data about data.” The data
dictionary of a database can be thought of as containing metadata for that
database. Although no universally accepted terminology exists to describe
metadata structures, the most popular set of terms is used in the entity-relationship
model. We will use that terminology to describe the components of metadata.
Later in this chapter, we will formally discuss the entity-relationship model.


A person, place, thing or event of importance to the
organization. Anything that can be a noun can be an entity.  (Hernandez, 2013)


Each entity has a number of characteristic or properties
called attributes. If enties are nouns, we can think of attributes as
adjectives describing characteristics of entities.

Identification of entity occurrences (Primary Key)

If the value of an attribute uniquely identifies an
occurrence of an entity, that attribute can serve as the primary key of an
entity (Redmond, Wilson and Carter, 2012) . To serve as a primary
key an attribute must be unique. It must be the case that no two occurrences do
or can have the same for the primary key attribute.

Candidate Key

When an entity does not have a single attribute that uniquely
identifies its occurrences, a combination of attributes may be used for
identification purposes. This type of primary key is called a candidated key.

Note that it is possible to have an entity class that does
not have a primary key. However, for several reasons we like to identify a
primary key for each entity class. A specific occurrence of an entity class can
be directly accessed only if it has a primary key whose value can be specified
by a user to identify the desired occurrence (Redmond, Wilson and Carter, 2012) . In addition, the
relational model uses primary keys as the mechanism to link related entity
classes together. Finally, examination of the relationship of attributes to the
primary key of a table is an important part of “normalization” of a
database. Normalization helps ensure that entity classes have been defined
appropriately and that the boundaries between entity classes have been drawn



A relationship between any two entities is defined by the
pair of associations that exist between them. There are three possible types of
relationship between two items: a one to one relationship, a one to many
relationship, or a many to many relationship. For example, in a supermarket
database the relationship between customers and orders is called one to many.


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