What is Data Base Model
1) A
database model defines the logical design of data.
2) It also
describes, in which manner data can be stored, organized and manipulated
3) It
describes the relationships between different parts of the data.
4) The most
common Data Base Models are
a.
Hierarchical Database Model
b.
Relational Database Model
c. Network
Database Model
The most
popular commonly used database model is the relational model,
uses a
table-based format.
hierarchical Database Model:
1) The
hierarchical database model organizes data in the form of tree like structure.
2) The
hierarchical data model ¡s a way of organizing a database with one-to-many
relationships.
3) The
structure is based on the rule that one parent can have many children but
children are
allowed only one parent.
4) The top
of the tree structure consist of a single node that does not have any parent,
is called
root node.
5) For
example, there is a president with many managers below them , and those
managers
have many employees below them, but each employee has only one
manager.
6) The query
must pass through root node on their way down the hierarchy.
7) The data
is stored as records which are connected to one another through links.
8) A record
is a collection of fields, with each field containing only one value.
9) The nodes
(records) are connected by lines. These lines are connection to the next
level of
more specific information.
Advantages
1) It allows
easy addition and deletion of new information.
2) Data at
the top of the Hierarchy ¡s very fast to access.
3) It was
very easy to work with the model because it worked well with linear type
data storage
such as tapes.
4) It
relates well to anything that works through a one-to-many relationship.
Disadvantages
It requires
data to be stored in many different entities.
2) The
database can be very slow when searching for information the lower
entities.
3) We no
longer use linear data storage mediums such as tapes, so that advantages
null.
4) Searching
for data requires the DBMS to run through the entire model from to
bottom until
the required information ¡s found, making queries very slow.
What is Data Independence in Database
Network Database Model:
1) A network
data base model the enhancement of
hierarchical database model.
2) This data
base structure is like a graph. This is similar to the hierarchical model
also
provides a tree-like structure. However, a child ¡s allowed to have more
one parent.
3) The
relationship that the record has in the network database model
many-to-many
relationship because one owner file can be linked to many member
files and
vice versa. .
4) In this
model some entities or records can be accessed through several paths.
5) For
example: consider an organization with an employee database, for e
employee
here are different pieces of data, such as name, address, telephone
number,
social security number etc.
6) Different
units in the organization need different levels of access. For example,
human
resources department needs to have access to the social security information
for each
employee so they can take case of tax deductions and set up benefits.
7) Network
database model was invented by Charles Bachman in 1969 as
enhancement
of already existing database model, the hierarchical database mode
What are the components of database system
8) The
Network database model is more flexible as compared to hierarchical mode
Advantages:
1) Because
it has the many-to-many relationship, network database model can
be accessed
in any table record in the database.
3) For more
complex data, it is easier to use because of the multiple relationship found
among its
data. .
3) Easier to
navigate and search for information because of its flexibility.
Disadvantages
1) Complex
in nature.
2)
Difficulties with alterations of the database because if information is entered
it can
alter the
entire database.
Relational Database Model:
1) The
relational database model is developed by “Edgar F.Codd” at IBM in 1970.
The
relational Database Model used the basic concept of a relation or table.
3) A table
is a collection of records and each record in a table contains the same fields.
4) Every row
or entity (called tuple) must have a unique identification or key based on
the data.
The
different tables may have the common column name (Attribute), but a single
table must
not contain multiple columns (Attributes) with the same name.
6) The
relationship between the two tables is implemented using a common and
unique
attribute in the tables. It doesn’t use physical links.
7) Columns
are attributes that belong to the entity modeled by the table.
8) In order
of rows (tuples/entities) and columns (attributes) is not important.
9) But every
tuple must be unique. It means that for every record or tuple in a table
there is
something that uniquely identified it from any other tuple.
10) Each
cell can contain only single value (value for attribute).
11) The
column (attribute) contains same types of values for every tuple.
12) The two
tables in the database must not have the same name. they can have some
column name
in common.