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every case that may be relevant to its class are provided, although some cases may have unknown
or non-applicable values for some attributes. There are 24 attributes in this example, but See5 can
deal with any number of attributes.
See5's job is to find how to predict a case's class from the values of the other attributes. See5 does
this by constructing a classifier that makes this prediction. As we will see, See5 can construct
classifiers expressed as decision trees or as sets of rules.
Application filestem
Every See5 application has a short name called a filestem; we will use the filestem hypothyroid
for this illustration. All files read or written by See5 for an application have names of the form
filestem.extension, where filestem identifies the application and extension describes the contents
of the file. The case of letters in both the filestem and extension is important -- file names
APP.DATA, app.data, and App.Data, are all different. It is important that the extensions are
written exactly as shown below, otherwise See5 will not recognize the files for your application.
Names file
Two files are essential for all See5 applications and there are three further optional files, each
identified by its extension. The first essential file is the names file (e.g. hypothyroid.names) that
describes the attributes and classes. There are two important subgroups of attributes:
•The value of an explicitly-defined attribute is given directly in the data. A discrete attribute
has a value drawn from a set of nominal values, a continuous attribute has a numeric value,
a date attribute holds a calendar date, a time attribute holds a clock time, a timestamp
attribute holds a date and time, and a label attribute serves only to identify a particular case.
•The value of an implicitly-defined attribute is specified by a formula. (Most attributes are
explicitly defined, so you may never need implicitly-defined attributes.)
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