The traditional taxonomy is monohierarchical – there is one and only one place for every term. This is only sensible for many purposes; no one wants to look up a book in a library catalog only to find out that it is either in Section A or Section F, and no biologist would ever identify a new species as being both a fungus and an animal. “A place for everything and everything in its place” is the guiding principle of the monohierarchical taxonomy.

But there are times when that guiding principle just isn’t appropriate.

Take synthetic biology, for instance. To some biologists, DNA is just a biopolymer – a biologically created compound made up of distinct smaller compounds. A synthetic biologist wouldn’t be likely to disagree with that characterization; DNA is a biopolymer, so the traditional biological taxonomy still stands. It is also a type of information storage. The traditional biologist wouldn’t disagree with that characterization either, but might question its relevance in building a biology taxonomy. When the synthetic biologist is designing devices that modify DNA strands to store data and other devices to read that data, though, it becomes relevant. DNA is a data medium as well as a biopolymer. It belongs with magnetic tape and optical discs as much as it does with cellulose and starches. In the same way, genetically engineered spider silk is both an animal product and an artificial fiber in equal measure – pigeonholing it into a specific location in the taxonomy keeps it out of an equally good location.

What about household electronics? By 2008, Sony’s Blu-Ray discs had overtaken Toshiba’s HD-DVDs and were clearly going to be the next generation video format of choice. But Blu-Ray players were still relatively rare and expensive. If you knew where to look, or even to look at all, one of the most economical options for a new Blu-Ray player was the Playstation 3. Unfortunately, even online retailers weren’t marketing the game console as a Blu-Ray player. A monohierarchical taxonomy at the retailer would obviously classify the systems as game consoles – that’s exactly what they were. But they were also functional and affordable Blu-Ray players. There’s no way of knowing for certain, of course, but it is entirely possible that online retailers like could have sold even more Playstation 3 consoles if their customers had seen the consoles as an option when searching for Blu-Ray players.

These aren’t isolated situations. Synthetic biology isn’t the only multidisciplinary field. Modern science includes chemical physics, astrophysics, neuroeconomics, and a whole host of other fields that draw from two or more distinct disciplines. The whole point of these multidisciplinary sciences is to study the places where the parent disciplines converge. Technological convergence is a real and growing trend. Microwave televisions may not be the wave of the future, but a smart oven that can bake a pie based on a recipe it downloaded off the internet and then call you on your cell phone when it’s done may be just around the corner; if your next oven comes from a computer manufacturer, where will it be listed in the online catalog?

Luckily, modern taxonomy has a tool to deal with that problem: polyhierarchy. In a polyhierarchical thesaurus, you might still find DNA in the traditional biological place, as a child term of biopolymers, but you might also find it as a child term of storage media. Likewise, you could find that Playstation 3 either by browsing the list of game consoles or by browsing the list of Blu-Ray players. It isn’t suitable for every situation, but it makes for a more flexible thesaurus that provides added value in many circumstances. An article on spider silk is tagged in a way that lets both the researcher interested in animal products and the one interested in artificial fibers know that it may be relevant. An online store search returns the microwave television in a search for either microwaves or televisions. The polyhierarchical thesaurus replaces “A place for everything and everything in its place” with “Everything goes every place it fits.”

Tim Soholt, Webmaster
Access Innovations, Inc.