Database Reference
In-Depth Information
Medina
Norton Soke
Old Medina Road S1
Isis
FIGURE 6.6
Dividing the Old Medina Road into sections.
The second problem with our statements is that they do not provide enough infor-
mation on their own to reconstruct the network. Does the order go Medina, Norton
Soke, Isis, or Norton Soke, Isis, Medina, or what?
To get around this, it is more normal to break the road up into sections as shown
in Figure 6.6 and then use these sections to connect the settlements:
Old Medina Road S1 is part of Old Medina Road.
Old Medina Road S2 is part of Old Medina Road.
Old Medina Road S1 is connected to Old Medina Road s2.
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Old Medina Road S1 is connected to Medina.
Old Medina Road S1 is connected to Norton Soke.
Old Medina Road S2 is connected to Norton Soke.
Old Medina Road S2 is connected to Isis.
It is now possible to reconstruct the connectivity.
In fact, it is normal to decompose a network connection for two main reasons:
to enable the network connectivity to be correctly expressed as in our example and
to enable properties to be associated with specific sections of the connection. In the
case of the Old Medina Road, one section of the road between Norton Soke and Isis
is single track, and we want to record this explicitly. To do so, we further break down
the road into four sections rather than two, as depicted in
Figure 6.7
.
The route between Norton Soke and Isis is then described as follows:
Old Medina Road S2 is connected to Norton Soke.
Old Medina Road S2 is connected to Old Medina Road S3.
Old Medina Road S3 is connected to Old Medina Road S4.
Old Medina Road S4 is connected to Isis.
Old Medina Road S2 has exactly 2 Lanes.
Old Medina Road S3 has exactly 1 Lane.
Old Medina Road S4 has exactly 2 Lanes.
