Identification keys

Identification keys

What is an identification key?

An identification key is a tool to assist a user identify an organism. It guides the user along a path towards an identification.

There are three main types of keys:

  • random access keys
  • pathway keys
  • hybrid keys

What is a random access key?

A random access key provides a list of the distinguishing features of the organisms in the key (in the case of crabs, this would be a set of the important features of different types of crabs). These features can be accessed in a random order and the keys are are usually computer-based, as a database is generally required to hold the key’s data.

An identification is performed by selecting from among the listed features those  that match your specimen; essentially, you describe the features of your specimen to the key. The tool then compares your described features against a database of the features of all the organisms in the key, and returns a list of those organisms that match your choices. As you choose answers to the questions asked by the key, the list of potential matches is progressively reduced.

For example, you may tell the key that your crab is brown, has a body covered in hairs and has claws that are more or less the same size. The key will list all brown, hairy, equal-clawed crabs. If only one crab matches this description, you will have completed the identification. Otherwise, there may be several crabs that match. Selecting further features may then help narrow the choice.

Random access keys available on the web include:

  • Lucid—several versions of Lucid exist. Good examples are at Lucid Central
  • DELTA—DELTA keys need to be played using a free player. A good set of DELTA keys is at the CrustaceaNet site of the Australian Museum
  • Navikey—a web-based key based on DELTA. A wide range of Navikey keys is at the Flora of China website
  • DiscoverLife – this website is building a set of keys called IDNature guides

What is a pathway key?

A pathway key asks specific questions about an organism in a specified order. The first question may be whether the claws of your crab are more or less the same size or are very unequal. Choosing ‘more or less the same size’ will lead to a second question, the answer to which will lead to a third, and so on. By answering questions in the order specified, the key will lead you along a pathway of successive questions. At the end of the path hopefully will be the name of your crab.

Pathway keys can be readily printed and are often, though not exclusively, found in books.

Examples of pathway keys are:

What is a hybrid key?

A hybrid key contains features of both random access and pathway keys. For example:

  • random access keys may include mechanisms to guide the user as to which question is best to answer next
  • computer-based keys may be used simply as a means of reducing the set of possible organisms to a small enough number that flipping through pictures of the remainder is likely to succeed.

The different types of keys are converging into a more flexible information environment. The ALA-supported IdentifyLifeis playing an important role in this process.

What are the strengths of each type of key?

Random access keys have the following strengths:

  • very flexible—you can address only the features that are most appropriate, in any order
  • often made to be very user-friendly, eg lots of images
  • may be able to handle an identification even if you have a very inadequate specimen
  • provide a great deal of guidance as you proceed through an identification
  • relatively quick and often easy to build
  • accurate and fast (when well constructed).

Pathway keys have the following strengths:

  • provide a great deal of guidance as you proceed through an identification
  • relatively quick and often easy to build
  • accurate and fast (when well constructed).

What are the weaknesses of each type of key?

Random access keys have the following weaknesses:

  • very prone to errors caused by inadequate or erroneous underlying data
  • tend to be expensive and time-consuming to build
  • often a steeper learning curve to use.

Pathway keys have the following weaknesses:

  • relatively inflexible
  • an identification will often be blocked if you can’t answer one question
  • hard to keep up-to-date as new species are discovered.