What kind of relationship does a network data model represent?

Network model in the database with examples and characteristics.

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What is the network model in dbms?
Example of a network model
Examples of network databases
Characteristics of the network model
Network model VS Hierarchical model VS Relational model:
Advantages of the network model
Disadvantages of a network model
Database systems
Further reading
External links

What is the network model in dbms?

When we want to design the database, there is a variety of database models. Relational, hierarchical, and network models are famous models. In this tutorial, we will explore the database network model.

The network database model is a model for modeling the entities in such a way that one child entity can have more than one parent entity. In 1969, the network model was presented by Charles Bachman.

Example of a network model

Figure: a network model

In this figure, we can see that the subject is the child class and student and degree are the parent classes.

So, the subject has two parent classes. STUDENT has one child and the Degree class also have one child.

This kind of relationship among entities represents the network model.

Examples of network databases

Examples of some famous network databases are,

TurboIMAGE
Integrated Data Store (IDS)
Raima Database Manager
Univac DMS-1100
IDMS (Integrated Database Management System)

Characteristics of the network model

There are many characteristics of the network model, some of these characteristics are mentioned below;

The network model is better than a hierarchical model.
Supports many to many relationships.
Many parents can have many children.
Many children can have many parents (as shown in the figure).
Entities are represented as a connected network with each other.
One child entity can have more than one parent entity. For example, in the figure, the Subject has two children. One child is a STUDENT and another one is Degree.
Represented as a network and one child can have more than one parent. This model represents a complex structure.
Entities can have multiple parent entities and lead to a complex structure.
Not very flexible to reorganize the model.
High performance
Relationships among databases are done by programmers by using 3GL programs.
Query facility is not available in the network model.

Network model VS Hierarchical model VS Relational model:

Network Data Model	Hierarchical Data Model	Relational Data Model
Pointers or links are used to express the relationship between records.	The relationship between records is of the parent-child type.	A relation(that contains a key for each record involved in the relationship) is used to represent the relationship between records.
It is possible to implement the Many to many relationships.	Many to many relationships cannot be expressed in Hierarchical Data Model.	It is easy to implement Many to many relationships.
No problem of inconsistency exists in the Network model.	The data inconsistency is possible when we update or delete some records.	7. Its needs to maintain Data integrity and consistency by maintaining the database Normalization. For example 1st NF, 2nd NF, 3rd NF, 3.5 NF, 4 NF, and so on.
Record relationship implementation is quite complex due to the use of pointers.	The method of implementing the record relationships is; · Simple · Natural · straightforward	The use of a key or composite key field plays a role in making the process easy for the implementation of relationships.
In-Network model record relations are physical.	The record relations are physical in the Hierarchical data model.	Data is organized logically in the form of rows and columns and stored in the table. The relational model does not maintain a physical connection among records.
Searching for a record is easy since there are multiple access paths to a data element.	Searching for a record is very difficult because we can retrieve a child only after going through its parent record.	A unique, indexed key field is used to search for a data element in a relation.
The network model is useful for representing such records that have many to many relationships.	The hierarchical Data Model is useful only when there is some hierarchical character in the database.	The relational model is useful for representing most of the real-world objects and relationships among the objects.

Advantages of the network model

It is fast data access with a network model.
The network model allows creating more complex and more strong queries as compared to the database with a hierarchical database model. A user can execute a variety of database queries when selecting the network model.
Sometimes, the network model is used to build computer network systems.
The network model is considered as an enhancement to the hierarchical database model.

Disadvantages of a network model

The network model is a very complex database model, so the user must be very familiar with the overall structure of the database.
Updating the database is a quite difficult and boring task. We need the help of the application programs that are being used to navigate the data.

1. Network model supports many to many relationships ? YES / NO

2. Network model is more complex than hierarchical model? YES / NO

3. Network model relationships are written in ………language?

(a) 1GL

(b) 2GL

(d) None of them

Database Models MCQs

Hierarchical Model

Network model

Network model Research Topics Ideas in DBMS

Database model invented by Charles Bachman

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Bachman diagram of a simple network database

The network model is a database model conceived as a flexible way of representing objects and their relationships. Its distinguishing feature is that the schema, viewed as a graph in which object types are nodes and relationship types are arcs, is not restricted to being a hierarchy or lattice.

The network model was adopted by the CODASYL Data Base Task Group in 1969 and underwent a major update in 1971. It is sometimes known as the CODASYL model for this reason. A number of network database systems became popular on mainframe and minicomputers through the 1970s before being widely replaced by relational databases in the 1980s.

Overview

While the hierarchical database model structures data as a tree of records, with each record having one parent record and many children, the network model allows each record to have multiple parent and child records, forming a generalized graph structure. This property applies at two levels: the schema is a generalized graph of record types connected by relationship types (called "set types" in CODASYL), and the database itself is a generalized graph of record occurrences connected by relationships (CODASYL "sets"). Cycles are permitted at both levels.

The chief argument in favour of the network model, in comparison to the hierarchical model, was that it allowed a more natural modeling of relationships between entities. Although the model was widely implemented and used, it failed to become dominant for two main reasons. Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in their established products such as IMS and DL/I. Secondly, it was eventually displaced by the relational model, which offered a higher-level, more declarative interface. Until the early 1980s the performance benefits of the low-level navigational interfaces offered by hierarchical and network databases were persuasive for many large-scale applications, but as hardware became faster, the extra productivity and flexibility of the relational model led to the gradual obsolescence of the network model in corporate enterprise usage.

History

The network model's original inventor was Charles Bachman, and it was developed into a standard specification published in 1969 by the Conference on Data Systems Languages (CODASYL) Consortium. This was followed by a second publication in 1971, which became the basis for most implementations. Subsequent work continued into the early 1980s, culminating in an ISO specification, but this had little influence on products.

Bachman's influence is recognized in the term Bachman diagram, a diagrammatic notation that represents a database schema expressed using the network model. In a Bachman diagram, named rectangles represent record types, and arrows represent one-to-many relationship types between records (CODASYL set types).

Database systems

Some well-known database systems that use the network model include:

IMAGE for HP 3000
Integrated Data Store (IDS)
IDMS (Integrated Database Management System)
Raima Database Manager
Univac DMS-1100
Norsk Data SIBAS
Oracle CODASYL DBMS for OpenVMS (originally known as DEC VAX DBMS)

References

David M, k., 1997. Fundamentals, Design, and Implementation. database processing ed. s.l.:Prentice-Hall.

External links

Wikimedia Commons has media related to Network models.

"CODASYL Systems Committee "Survey of Data Base Systems"" (PDF). 1968-09-03. Archived from the original (PDF) on 2007-10-12.
Network (CODASYL) Data Model
SIBAS Database running on Norsk Data Servers

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