Hierarchical Model - A hierarchical database is similar in nature to a file system, with a root or parent node and one or more children referencing the parent. This makes for a very fast
data-access path.
The hierarchical model organizes data elements as tabular rows, one for each instance of an entity. Consider a company's organizational structure. At the top we have a General Manager (GM). Under him we have several Deputy General Managers (DGMs). Each DGM looks after some departments and each department will have a manager and many employees. When represented in hierarchical model, there will be separate rows for representing the GM, each DGM, each department, each Manager and each Employee. The row position implies a relationship to other rows. A given employee belongs to the department that is closest above it in the list and the department belongs to the manager that is immediately above it in the list and so on.
it has the disadvantages of low flexibility, lack of an ad-hoc
query capability, and high application maintenance.
Data integrity Since the hierarchical model is based on the parent Childes relationship, there is always a link between the parent segment and the child segments under it The child segments arc always aromatically referenced to its parent.
data-access path.
The hierarchical model organizes data elements as tabular rows, one for each instance of an entity. Consider a company's organizational structure. At the top we have a General Manager (GM). Under him we have several Deputy General Managers (DGMs). Each DGM looks after some departments and each department will have a manager and many employees. When represented in hierarchical model, there will be separate rows for representing the GM, each DGM, each department, each Manager and each Employee. The row position implies a relationship to other rows. A given employee belongs to the department that is closest above it in the list and the department belongs to the manager that is immediately above it in the list and so on.
it has the disadvantages of low flexibility, lack of an ad-hoc
query capability, and high application maintenance.
Data integrity Since the hierarchical model is based on the parent Childes relationship, there is always a link between the parent segment and the child segments under it The child segments arc always aromatically referenced to its parent.
No comments:
Post a Comment