Page 184 - DCAP312_WEB_TECHNOLOGIES_II

Web Technologies-II

Notes 9.3 Network Database Model

The hierarchical data model represent well any business data that intrinsically contains levels one
below the extra. We have just discussed how the developed application deals with hierarchical
levels of plant record with assemblies broken down into buried components. The hierarchical
data model suits this application well. However, in the real world, most data structures do
not conform to a hierarchical arrangement. The levels of data structures do not fall into nice
dependencies one below another as in a hierarchy. In the hierarchical data model, you have
noticed that each data segment at any level can have only one parent at the next higher level.
In practice, many sets of related elements may not be subjected to such restrictions.

Let us consider a common set of related data elements in a typical business. The data elements
pertain to customers placing orders and making payments, salespersons being assigned, and
salespersons being part of sales territories. All of these data elements cannot be arranged in a
hierarchy. The relationships cross over among the data elements as though they form a network.
Refer to Figure 9.2 and note how it represents a network arrangement and not a hierarchical
arrangement. Observe the six data elements of sales territory, salesperson, customer, order,
order line item, and payment as nodes in a network arrangement.

Figure 9.2: Network Data Model

Owner Member Owner
record type
record type record type
SALES CUSTOMER
TERRITORY
Owner
Member record type
record type
ORDER PAYMENT
Member
record type
SALES
PERSON Member Owner
record type record type
Owner ORDER
record type
LINE ITEM
Relationship links Member
through physical record type
pointers

The network data model overcomes some of the limitations of the hierarchical data model. The
network data model is more representative of real-world information requirements than the
hierarchical model. The network data model can represent most business information.
Let us go over the key features of the network model by referring to Figure 9.2.
9.3.1 Levels

As in most real-world situations, no hierarchical levels exist in the network model. The lines
in a network data model simply connect the appropriate data structures wherever necessary
without the restriction of connecting only successive levels as in the hierarchical model. Note
the lines connecting the various data structures with no restrictions.

9.3.2 Record Types
In the network data model, each data structure is identified as an evidence type. For example,
the CUSTOMER record type represents the data content of all customers. The ORDER record
type represents the data content of all orders.

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