Network Model in DBMS

Network Model :
This model was formalized by the Database Task group in the 1960s. This model is the generalization of the hierarchical model. This model can consist of multiple parent segments and these segments are grouped as levels but there exists a logical association between the segments belonging to any level. Mostly, there exists a many-to-many logical association between any of the two segments. We called graphs the logical associations between the segments. Therefore, this model replaces the hierarchical tree with a graph-like structure, and with that, there can more general connections among different nodes. It can have M: N relations i.e, many-to-many which allows a record to have more than one parent segment.
Here, a relationship is called a set, and each set is made up of at least 2 types of record which are given below:

• An owner record that is the same as of parent in the hierarchical model.
• A member record that is the same as of child in the hierarchical model.

Structure of a Network Model :

A Network data model

In the above figure, member TWO has only one owner ‘ONE’ whereas member FIVE has two owners i.e, TWO and THREE. Here, each link between the two record types represents 1 : M relationship between them. This model consists of both lateral and top-down connections between the nodes. Therefore, it allows 1: 1, 1 : M, M : N relationships among the given entities which helps in avoiding data redundancy problems as it supports multiple paths to the same record.  There are various examples such as TOTAL by Cincom Systems Inc., EDMS by Xerox Corp., etc. 

Example : Network model for a Finance Department.

Below we have designed the network model for a Finance Department :

Network model of Finance Department.

So, In a network model, a one-to-many (1: N) relationship has a link between two record types.  Now, in the above figure, SALES-MAN, CUSTOMER, PRODUCT, INVOICE, PAYMENT, INVOICE-LINE are the types of records for the sales of a company. Now, as you can see in the given figure, INVOICE-LINE is owned by PRODUCT & INVOICE. INVOICE has also two owners SALES-MAN & CUSTOMER. 

Let’s see another example, in which we have two segments, Faculty and Student. Say that student John takes courses both in CS and EE departments. Now, find how many instances will be there?

For the above example, a students instance can have at least 2 parent instances therefore, there exist relations between the instances of students and faculty segment. The model can be very complex as if we use other segments say Courses and logical associations like Student-Enroll and Faculty-course. So, in this model, a student can be logically associated with various instances of Faculties and Courses.

Advantages of Network Model :

• This model is very simple and easy to design like the hierarchical data model.
• This model is capable of handling multiple types of relationships which can help in modeling real-life applications, for example, 1: 1, 1: M, M: N relationships.
• In this model, we can access the data easily, and also there is a chance that the application can access the owner’s and the member’s records within a set.
• This network does not allow a member to exist without an owner which leads to the concept of Data integrity.
• Like a hierarchical model, this model also does not have any database standard,

Disadvantages of Network Model :

• The schema or the structure of this database is very complex in nature as all the records are maintained by the use of pointers.
• There’s an existence of operational anomalies as there is a use of pointers for navigation which further leads to complex implementation.
• The design or the structure of this model is not user-friendly.
• This model does not have any scope of automated query optimization.
• This model fails in achieving structural independence even though the network database model is capable of achieving data independence.