Semantic networks provide structure to a set of concepts, as a network or a web. They are often defined as graph representations of the relationships among sets of concepts. In a larger sense, in the world of computer science, they are sets of concepts with relationships that are defined in such a way that computers, or the World Wide Web, can work with those relationships.

Semantic networks need to be built on top of something else. The semantic networks are made to form a web, or a web of knowledge. As we know, there are lots of ways to think about knowledge, lots of ways to approach it, but at the end of the day it is the concepts themselves that form the nodes on the web – meaning the intersection of the data. To build the web we need to find a way to create a node and then make the relationships. Those relationships might be the broader and narrower terms from a thesaurus or taxonomy. They might be the synonyms and they might be the hierarchies from another column or another table providing a way to flesh out the information. You can show all kinds of cause and effect kinds of relationships, whole/part ownership, and things like that in that kind of expansion. This expanded network of terms and relationships is made possible with computer technology. It would take individuals much longer to figure them out and make the connections.

The concepts in a semantic network can be thought of as nodes, with various relationships branching out from those nodes. The expanded relationships can be ones that taxonomists and ontologists are familiar with, such as specific whole-part relationships, cause-effect, and parent-child.

Princeton University’s WordNet is often used as a source for this work; it appears in several search engines. However, WordNet is really a synonym gradient, rather than a true semantic network in the full sense. To my mind, it does not lend itself to use as a semantic web, but some people will mention WordNet in the same breath as “semantic web,” so I want you to understand the difference between them. If you are looking for the sense of a term, or looking for simple ways to expand terms (and if you can’t afford to buy the American Heritage Dictionary, which is the other one that people frequently invoke) then using a variation on WordNet, which is available fairly inexpensively, is a good option.

To a geneticist, “recombination” may seem perfectly clear, and in no need of clarification. He or she may automatically think of genetic recombination, in which DNA strands break and rejoin in different ways. Even for other geneticists with a different specialty within genetics, though, “recombination” may have something to do with genetic algorithms and chromosomes. If the taxonomy covers various sciences and not just genetics, “recombination” could trigger any of the following, as indicated on the Wikipedia disambiguation page for Recombination (bless Wikipedia for their disambiguation pages, even though they need to be taken with a grain of salt): in genetics (as mentioned above), the process by which genetic material is broken and joined to other genetic material; in semiconductor physics, the elimination of mobile charge carriers (electrons and holes); in plasma physics, the formation of neutral atoms from the capture of free electrons by the cations in a plasma; in cosmology, the time at which protons and electrons formed neutral hydrogen in the timeline of the Big Bang; in chemistry, the opposite of dissociation.  This underscores the need to find out what whomever you are working with means.

Marjorie M.K. Hlava
President, Access Innovations

Note: The above posting is one of a series based on a presentation, The Theory of Knowledge, given at the Data Harmony Users Group meeting in February of 2011. The presentation covered the theory of knowledge as it relates to search and taxonomies.