What is Network Model | What is Relational Model ?

• What is Network Model ?

1. The network data model was developed to overcome the limited ca hierarchical model. Here, multiple parernt-child relationships are used.
   
   
2. The original network model and larnguage were presented in the Con. (Conference on Data Systems Languages) through its Data Base Task Group (DRTC DASYL is sometimes called the DBTG model. 
   
   
3.  The network model uses a network structure, which is a data structure consisting ot nodes and branches.
   
   
4.  In this model, there is no distinction between parent and child nodes as in the hierarchical model. Each node may be related to more than one node.
   
   
5.  In this model, directed graphs are used instead of tree structure to represent the structure of database. Here, records appearing as nodes and relationships as edges the graph.
   
   
6.  The main difference of network model with hierarchical model is that a netwOn model permits a child node to have more than one parent nodes, Wnere hierarchical model does not allows a child node to have multiple parent nodes.
   
   
   
   
   

• Advantages of Network Model:-  

1. Conceptual Simplicity: Like hierarehical model, network model is also simple and easy to implement.
   
   
2. Capability to handle more relationship types: The network model can handie one to one (1:1) and many to many (N: N) relationship.
   
   
3.  Ease to access data: Rapid and easy access to data is possible in this model due to multiple acoess paths to the data elenments.
   
   
4.  Data Integrity: Since it is based on the parent child relationship, there is always a link between the parert segment and the child segment under it.
   
   
5.  Data Independence: The network model is better than hierarchical model in case of data independence.
   
   

• Disadvantages of Network Model :-  

1. System Complexity: All the records have to maintain using pointers thus the database structure becomes more complex.
   
   
2.  Operational Anomalies: As discussed earlier in network model large number of pointers is required so insertion, deletion and updating more complex.
   
   
3.  Absence of structural Independence: There is lack of structural independence because when we change the structure then it becomes compulsory to change the application too.
   
   

• What is Relational Model ?
  

1. The most popular data model in DBMS is the Relational Model. The principles of the relational model were first outlined by Dr. E. F. Codd in a June 1970.
   
   
2.  The relational model is considered as one of the most popular developments in the database technology because it can be used for representing most of the real world objects and the relationships between them.
   
   
3.  In relational model, data is organized in terms of rows and columns in a table known as relation. Each table consists of rows aliso known as tuples .
   
   
4. Any two tables can be linked irrespective of hierarchical placement. Therefore, any table can be accessed directly without having to access child tables through a hierarchy or network of parent tables.
   
   
5.  The relational database relates or connects data in different tables through the use of a common field or attribute.
   
   
6.  This model doesn't require any information that specifies how the data should be stored physically.
   
   
7.  Relatively complex and efficient data structures can be created with the relational data model .
   
   

• Advantages of Relational Model :-  
  

1. Conceptual Simplicity: We have seen that both the hierarchical and network models are conceptually simple, but relational model is simpler than both of those two.
   
   
2. Design Impleme mentation: The relational model achieves both data independence and structural independence.
   
   
3. Ad hoc query capability: The presence of very powerful, flexible and easy to use capability is one ot the main reasons for the immense popularity of the relational database model.
   
   
4.  Security: Security control and authorization can also be implemented more easily by moving sensitive attributes in a given table into a separate relation with its own authorization controls.
   

• Disadvantages of Relational Model :-
  

1. Hardware overheads: Relational database systems hide the implementation complexities and the physical data storage details from the user. For doing this, the relational database system need more powerful hardware computers and data storage devices. .
   
   
2. Cost: One disadvantage of relational databases is the expensive of setting up and maintaining the database system. In order to set up a relational database, you generally need to purchase special software.
   
   
3.  Ease of design can lead to bad design: The relational database is easy to design and use. The user needs not to know the complexities of the data storage. This ease of design and use can lead to the development and implementation of the very poorly designed database management system.
   
   

• What is Semantic Data models ?

          The Semantic Data Model (SDM), like other data models, is a way of organizing data to represent it in a logical way.
          SDM differs from other data models, however, in that it focuses on providing more meaning of the data itself, rather than primarily on the relationships and attributes of the data.
          This model provides a high-level understanding of the data by abstracting it further away from the physical aspects of data storage.

            In semantic data model, an entity represents some aspect or item in the real world, such as an EMPLOYEE. These entities in SDM focus on types, which are more general, instead o sets of data.                  For instance, a semantic data model entity type might be PERSON, which provides an elementary category that can be easily understood. In a relational model, however, you might end up with a number of different tables including- person, spouse, children, house, ana Each of these things represents part of what makes up the person, but with SDM, the cPSON is the whole entity, rather than breaking it down into parts.

           In this way, an entity in SDM is very similar to a domain. Therefore, inside this domain of PERSON, PERSON there would be a list of names of people that are to be represented by the data. objects in this domain would then point to specific instances of a person that are The objects in this represented by eacn person entity. For example, the domain PERSON contains name Rahul, repre Sunny, Jimmy, and John. Each of these names points to a specific object instance of PERSON, so that Rahul points to a record giving detail about Rahul, such as name, gender, or marital status, and so on for each of the entities listed under PERSON.

• What is Entity-Relationship Model (E-R MODEL) ?
  

        Entity-Relationship Model (E-R Model) is a high-level conceptual data model developed by Peter Chen in 1976 to facilitate database design. Conceptual Modeling is an important phase in designing a successful database. A conceptual data model is a set of concepts that describe the structure of a database and associated retrieval and updation transactions on the database. The E-R model is the generalization of the earlier available commercial models ike the Hierarchical and the Network Model.                      So to sum up, the Entity-Relationship (E-R) Model is based on a view of a real world that consists of set of objects called entities and relationships among entity sets which are basically a group of similar objects. The relationships between entity sets is represented bya named E-R relationship and is of 1:1, 1: N or M: N type which tells the mapping from one entity set to another. 

                    A basic component of the E-R model is the Entity-Relationship diagram which is used to visually represent data objects and the relationships between them. 

•  Features of the E-R Model :-
  

1. The E-R diagram used for representing E-R Model can be easily converted into relations (tables) in relational model.
   
   
2.  The E-R Model is used for the purpose of good database design by the database developer so to use that data model in various DBMS.
   
   
3.  It is helpful as a problem decomposition tool as it shows the entities and the relationship between those entities.  
   
   

•  Entities and Attribute :-
  

1. The basic object that the ER model represents is an entity, which is a "thing" in he real world with an independent existence. An entity may be an object with a physical existence- a particular person, car, house etc. or it may be an object witha conceptual existence- a company, a job, or a university course.
   
   
2.  Each entity has attributes- the particular properties or characteristics that describe it. For example, an EMPLOYEE entity may be described by its attributes- rname, age, address, salary, and job. A particular entity will have a value for each of its attr+butes. The attribute values that describe each entity become a major part of the data stored in the database.