Database Reference
In-Depth Information
Order Detail
Customer
Following figure shows the contents of selected records within the hierarchical model
design. The record for customer
Surjeet
has a pointer to its first order (ID 101), and that
order has a pointer to the next order (ID 110). We know that Order 110 is the last order for
the customer because it does not have any pointers to additional orders. Looking at the next
layer in the hierarchy, Order 30 has a pointer to its first Order Detail record (for Product
38), and that record has a pointer to the next detail record, and forth.
Characteristics of a hierarchical model
The characteristics of a hierarchical model are listed below:
All child node occurrences can use the data of their parent node occurrences All child
nodes are deleted with the deletion of parent node.
Root node may have multiple child nodes.
A child node has only one parent node.
There are three major drawbacks to the hierarchical model:
1. Not all situations fall into the one-to-many, parent-child format.
2. The choice of the way in which the files are linked impacts performance, both positively
and negatively.
3. The linking of parent and child records is done physically. If the dependent file were re-
organized, then all pointers would have to be reset.
2.1.3 Network Database Model
A network database model organizes files in a manner that associates each file with
n
num-
ber of other files. This approach uses pointers to create a relationship between records in
