Extracting features is one of the most critical tasks in data mining, and it generally affects your end result more than the choice of data mining algorithm. Unfortunately, there are no hard and fast rules for choosing features that will result in high performance data mining. In many ways, this is where the science of data mining becomes more of an art. Creating good features relies on intuition, domain expertise, data mining experience, trial and error, and sometimes a little luck.
Not all datasets are presented in terms of features. Sometimes, a dataset consists of nothing more than all of the books that have been written by a given author. Sometimes, it is the film of each of the movies released in 1979. At other times, it is a library collection of interesting historical artifacts.
From these datasets, we may want to perform a data mining task. For the books, we may want to know the different categories that the author writes. In the films...