Data Models
A data model is a collection of concepts that can be used to describe the structure of a
database whereas structure of a database means the data types, relationships and constraints
that should hold on the data.
A
database model
determines in which manner data can be stored, organized, and
manipulated in a database system. A database model is a theory or specification describing how a
database is structured and used. Several such models have been suggested.
Common types of data models include:
1.
Record-Based Data Models
a.
Hierarchical model
b.
Network model
c.
Relational model
2.
Object-Based Data Models
a.
Object-relational model
b.
Semantic
c.
Entity-relationship
3.
Physical Data Models
Record-Based Data Models
Hierarchical model
The hierarchical data model organizes data in a tree structure. There is a hierarchy of
parent and child data segments known as Record Type. Data in a series of records, which have a
set of field values attach to it. It collects all the instances of a specific record together as a
record type. These record types are the equivalent of tables in the relational model, and with
the individual records being the equivalent of rows. To create links between these record types,
the hierarchical model uses Parent Child Relationships. These are a 1:N mapping between
record types. For example, an organization might store information about an employee, such as
name, employee number, department, salary. The organization might also store information
about an employee's children, such as name and date of birth. The employee and children data
forms a hierarchy, where the employee data represents the parent record type and the children
data represents the child record type. If an employee has three children, then there would be
three child segments associated with one employee segment. In a hierarchical database the
parent-child relationship is one to many. This restricts a child segment to having only one parent
