5. A computer system for categorizing information items in a data storage and retrieval system, wherein each of said information items is associated with at least one property, said system including a computer readable memory having program code stored thereon, said program code comprising: program code for applying a global property ordering to each list of properties required for membership in each corresponding one of a currently defined set of categories; program code for generating a tree structure providing an index, wherein said tree structure indexes said currently defined set of categories based on said properties required for membership in corresponding ones of said categories, wherein said tree structure includes generating a plurality of nodes, each node being associated with an individual property and a list of categories, wherein said nodes are ordered within said tree structure based on said global property ordering, and wherein each category in said category list for each node is a category that requires the property associated with the node as well as the properties associated with all ancestor nodes of the node in the up direction for membership in that category; program code for receiving an input one of said information items; program code for selecting a subset of said defined set of categories to be checked by ordering all properties associated with said input information item into an ordered property list based on said global property ordering, and traversing said tree structure according to said ordered property list, wherein said traversing is limited to subtrees of said tree structure having nodes associated with properties in said ordered property list, wherein subtrees of said tree structure having nodes not associated with properties in said ordered property list are not traversed; and program code for categorizing said information item based on said selected subset of categories by checking the properties in said ordered list of properties to determine whether conditions for membership in each of said selected subset of categories are met, wherein conditions for membership in those categories not within said selected subset of categories are not checked.
5. A computer system for categorizing information items in a data storage and retrieval system, wherein each of said information items is associated with at least one property, said system including a computer readable memory having program code stored thereon, said program code comprising: program code for applying a global property ordering to each list of properties required for membership in each corresponding one of a currently defined set of categories; program code for generating a tree structure providing an index, wherein said tree structure indexes said currently defined set of categories based on said properties required for membership in corresponding ones of said categories, wherein said tree structure includes generating a plurality of nodes, each node being associated with an individual property and a list of categories, wherein said nodes are ordered within said tree structure based on said global property ordering, and wherein each category in said category list for each node is a category that requires the property associated with the node as well as the properties associated with all ancestor nodes of the node in the up direction for membership in that category; program code for receiving an input one of said information items; program code for selecting a subset of said defined set of categories to be checked by ordering all properties associated with said input information item into an ordered property list based on said global property ordering, and traversing said tree structure according to said ordered property list, wherein said traversing is limited to subtrees of said tree structure having nodes associated with properties in said ordered property list, wherein subtrees of said tree structure having nodes not associated with properties in said ordered property list are not traversed; and program code for categorizing said information item based on said selected subset of categories by checking the properties in said ordered list of properties to determine whether conditions for membership in each of said selected subset of categories are met, wherein conditions for membership in those categories not within said selected subset of categories are not checked. 6. The system of claim 5 , wherein said program code for selecting is responsive to receipt of said information item.