What is Hierarchical Database System ?
Hierarchical database system keeps the data in teh form of a parent child relationship. The datas is organised as a Tree structure. The origin of a data is the root of the data tree. The data occupies with different level of the particular branch of the tree called the node. The last node in the structure is called leaf. The high level node points to zero or more node in the next level. Each child has pointers to numerous siblings.
What is Network Database System ?
In this model data are represented by a collection of records and the relationships among data are represented by links NDS is supporting Many to Many relationship.
Disadvantages of Network Database System
1) Pointers create the complexity of the model.
2) It requires more space for keeping pointer value.
What is Relation Database System ?
A data-model in which both data and their relationships are represented by means of tables is called Relational model.
The relation is the only data structure used in this model to represent both entities and their interrelationships. A relation is a two dimensional table with a unique name.
Each row of a table is called a tuple and each column of a table is called an attribute. The set of all possible values in an attribute is called the domain of the attribute.
Disadvantages of Relation Database System
1) Resuability of the structure is not possible
2) Alteration of the structure is difficult
3) Maintenance of the structure is a continuous process
What is Object Based Relational Model ?
In this model the data are organized as an object. Each object has a set of value based on their class. The data structure of the object is called Class.
Advantages of Object Based Relational Model
1) Reusability of the structure is possible.
2) This model supports to define interface for the application
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