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86 4 The Semantic Web and Bioinformatics Applications

Figure 4.8 An example in which two resources are inferred to be the same. In this

case the ontology allows a gene to belong to at most one species. As a result if a gene

is linked to more than one species, then all of them must be the same. The inferred

relationship is shown in gray.

occurring as a result of other facts and rules. In general, one can reduce

spurious inferences in two ways:

1. Never overspecify. Declaring thatoccursInis a functional property is
   too strong. It may be true nearly all of the time, but even one exception
   can result in spurious inferences.


2. Specify distinctions. Explicitly declare that resources are different when
   they are known to be distinct. However, only specify this if one is re-
   ally sure that the resources are different. It does sometimes happen that
   entities such as diseases and proteins that were once thought to be dif-
   ferent subsequently turn out to be the same and the consequences can be
   profound.

Specifying that resources are different can get very tedious if there is a

large number of them. To deal with this problem, OWL has a mechanism for

specifying that a list of resources are all different from one another. For exam-

ple, the two species above could have been declared to be different by using

theowl:AllDifferentresource andowl:distinctMembersproperty

as follows:

<AllDifferent>

<distinctMembers parseType="Collection">

<Gene rdf:about="#D.rerio">

<Gene rdf:about="#D.danglia">

</distinctMembers>

</AllDifferent>