Admittedly, I only read up to the end of the claims section here: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2F

Admittedly, I only read up to the end of the claims section here: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,893,120.PN.&OS=PN/5,893,120&RS=PN/5,893,120 http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sec... If you read those and skim to see passages like these: "The problem, then, is to provide the speed of access of hashing techniques for large, heavily used information storage systems having expiring data and, at the same time, prevent the performance degradation resulting from the accumulation of many expired records. Although a hashing technique for dealing with expiring data is known and disclosed in U.S. Pat. No. 5,121,495, issued Jun. 9, 1992, that technique is confined to linear probing and is entirely inapplicable to external chaining. The procedure shown there traverses, in reverse order, a consecutive sequence of records residing in the hash table array, continually relocating unexpired records to fill gaps left by the removal of expired ones. Unlike arrays, linked lists leave no gaps when items from it are removed, and furthermore it is not possible to efficiently traverse a singly linked list in reverse order. There are significant advantages to external chaining over linear probing that sometimes make it the method of choice, as discussed in considerable detail in the aforementioned texts, and so hashing techniques for dealing with expiring data that do not use external chaining prove wholly inadequate for certain applications. For example, if the data records are large, considerable memory can be saved using external chaining instead of linear probing. Accordingly, there is a need to develop hashing techniques for external chaining with expiring data. The methods of the above-mentioned patent are limited to arrays and cannot be used with linked lists due to the significant difference in the organization of the computer's memory." The triviality of the patent should be fairly evident (but if I've jumped to a bad conclusion, I'm happy to be corrected). Fair point though!