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
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
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.
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.
It requires data to be stored in many different entities.
2) The database can be very slow when searching for information the lower
3) We no longer use linear data storage mediums such as tapes, so that advantages
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.
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
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
8) The Network database model is more flexible as compared to hierarchical mode
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.
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 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.