One possible problem of the IGUANA addressing schema is that the hierarchy may not be very structured in cases of house installations where a small number of fieldbuses contain a large number of nodes. This way, the third level of the hierarchy will be very large and difficult to overlook. Moreover, the addressing schema gives only a technical perspective of the fieldbus. In many cases, other views, such as geographical or logical would be more appropriate.
This problem could be solved by creating custom hierarchies, as shown in figure 44. A similar technique, called ``reference nodes'' is also suggested by [BACNET/WS]. However, ESD and the IGUANA gateway do not support such additional addressing schemes, which means that logical hierarchies would have to be implemented by the Web Service itself. Moreover, such hierarchies would have to be configured at start up and during operation, in case new fieldbus nodes are added or removed.
[VEN05] suggests to configure a logical hierarchy by using metadata provided by the fieldbus. The problem with this approach is that it is fieldbus specific and may not be possible for different fieldbus systems98. The IGUANA gateway is meant to be generic and not fieldbus specific, therefore the use of metadata for building logical hierarchies contradicts its design.