What is an interactive key?

Traditional printed dichotomous keys offer the user a series of paired contrasting “couplets,” arranged in a fixed sequence, that lead the user though a series of choices of characteristics about a particular organism. For example,

1 With wings
  Without wings
2 With two pairs of wings
  With one pair of wings
3 Forewings membranous
  Forewings modified as hardened elytra
4 Forewings covered with scales
  Forewings covered with hairs

Starting at couplet 1, the user observes the specimen in hand to determine if it has wings of not. If not, the identification is made and the specimen is a collembolan. If the specimen has wings, the user is directed to go to couplet 2 for an additional choice of characters, and so on. Of course, dichotomous keys are usually associated with illustrations or photographs to aid the user, and there can be more than one character included within a couplet. For example,

1 With wings (Fig. 1); without a jumping mechanism or furculum on the abdomen
  Without wings; with a jumping mechanism or furculum on the abdomen (Fig. 2)

Dichotomous keys are a type of single-access key in that the user enters the key at only one place, in this case at couplet 1, and works though the key one couplet at a time until an identification is made. Most taxonomic keys published today are dichotomous and while there are strengths and weakness of dichotomous keys, they offer a powerful tool for identifying organisms (Winston 1999).

Interactive keys, on the other hand, offer a completely different approach to identification. Interactive keys are computer based and are written and accessed through specifically designed software (INTKEY and Lucid, being perhaps the most popular interactive key applications in use today, but there are others). Interactive keys are structured on a feature by entity matrix. Each entity is scored for a particular characteristic or feature it possesses. For example,

Coleoptera Collembola Diptera Hemiptera Odonata Trichoptera
no wings  
one pair    
two pairs, forewings elytra
two pairs, forewings hemelytra      
two pairs, forewings membranous        

Features contain a varying number of states. For example, the feature antennae might have the states capitate, clavate, filiform, etc. In biology, these are referred to as characters and character states, and generally refer to morphological structures, but features can pertain to inanimate objects as well (soil types, cloud formations, bones, etc.). Similarly, in biology, entities are usually species or higher taxa, in this case aquatic insect orders.

One advantage to interactive keys is that the matrix can be scored to account for user error, uncertainty, misinterpretation of a state, or rare features, among others. For example, damselfly nymphs have three caudal tracheal gills at the end of the abdomen, but these are easily broken off collected specimens. The matrix can accommodate this fact by scoring the state as “present” (commonly) or as “absent” (misinterpreted). While the matrix forms the backbone of the key, it is not seen or accessed by the user. Instead the user accesses or “plays” the key through an additional application of the software and is presented with a choice of features and their states. States pertaining to the specimen in hand are chosen by the user, and entities that do not pertain to those states are sequentially eliminated until only one entity remains - the answer!

A second advantage of interactive keys is that they are multi-access. The user is not required to enter the key at only one point, and follow a standard, fixed sequence of couplets as in a dichotomous key. Instead, the user can enter the key at any available feature and proceed to any other available feature. On the other hand, most interactive key software comes with a powerful set of automated tools to guide the user through the best choice of features to identify an entity (these are explained in the tutorial

A third, but not final, advantage of interactive keys is that images, photographs, html files, hyperlinks, and other media can be easily attached to the key and accessed by the user at any time during the identification process.

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