1. A computer comprising: a semantic network ( 104 ) comprising a first semantic network element ( 105 ) associated with a first index ( 113 ) and a link ( 106 ) that refers to the first semantic network element; an index maintainer ( 107 , 115 ) coupled to at least one omission rule ( 108 , 116 ) configured to determine for the link whether the link is to be included in an index associated with a semantic network element that the link references; and a clusterer ( 111 ) configured to cause related objects to be clustered near each other in an address space of the computer; wherein the clusterer causes the link to be clustered with the first semantic network element in response to the index maintainer adding the link to the first index and omitting the link from an index associated with another node that the link refers to.