Data models
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[edit] Data Models
Data models are the set of concept to describe the structure of the database, and certain constraints that the database should obey.
[edit] Categories of Data Models
1.Conceptual
-High Level,semantic
-Abstract state
-Highly philosophical,away from reality
-It can be idea or notion in mind
2.Physical
-Low level, internal
3.Implementation
-Representation
[edit] Relational model
1.Logical relationship
2.Predicale calculus. R1(X,Y)----R2(A,B).This relationship can be define more logically using the relational model.
3.Data is organized in the forms of rows and column similar to table.
4.Columns of table are called attributes.
5.In this model,we group the data items in one or more independent table that can be related to each other through common field.
Advantages of Relational model
1.Efficient,effective even with limited memory and processing capacity.
2.It has variety in enquires to the database.
3.It is concerned with data not with structure so this improves the performance.
4.It uses pointer to implement record relationship.
5.It represent to real world objects.
Disadvantages of Relational model
1.Relational model does not allow nested structure.Nested structure are required in CAD/CAE.
2.It support limited number of data types like char,integer,text.
3.It is impossible to represent every information in table.
[edit] Hierarchical Model
1.It was developed by IBM in 1968.
2.Tree like structure with records forming the nodes and fields forming the branches of the trees.
3.This type of model is natural, structured, simple, straightforward.
4.Accountability is clear, priority is defined.
Disadvantages of Hierarchical model
1.It is rigid model.
2.It cannot represent the real world.
3.In this model, there is problem in inserting and deleting anomaly.
4.There is little scope of query optimization.
5.Database is visualized as the linear arrangement of records.
[edit] Network Model
1. It was given by Honeywell in 1964-65.
2.Data is represented by records using links among them.
3.It is similar to hierarchical except that an entity can have more than one parent.
Advantage of Network model
1.It can represent 1 to many relationship.
2.It is consistent model.
3.Search is easy as there are multiple access path to data elements.
4.Language is navigational.
Disadvantage of Network model
1.It is very complex model.
2.Insertion,deletion and updation of any record requires pointer adjustment.
3.Little scope for query optimization.
4.There is also difficulty in moving through nodes.
