Mailing Lists Account wrote:
Generally speaking, stemmers increase recall but decrease precision. Different stems of a word frequently have slightly different meanings, and are used in different contexts: hence the loss of precision. Internet search engines are not interested in increasing recall (there are usually plenty of matches) rather their problem is increasing precision (finding the best matches). For example, there are enought sites explicitly about "cars" that there's no need to conflate these with sites that are also about "car".Doug Cutting wrote:That's because Google and most internet search engines never do any stemming.Generally speaking, are there any advantages not to apply the stemmer ? Except for certain keywords,I found use of stemmers helpful.
However, with smaller collections, recall can be a problem and stemming can be useful. A higher percentage of false positives is returned with stemming (decreased precision) but in a small collection that's acceptable if it also finds a few more relevant documents (increased recall).
I suspect the reason that internet search engines do not permit wildcards is simply a performance issue: wildcarded terms can be *much* more expensive to process, and internet search engines cannot afford them.
Doug
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