Taught the computer how natural languages work, for one thing. Its tokenizer picks words out of text, dealing with commas and hyphens correctly. This tokenizer is als o language-independent, since all human languages share universal linguistic properties. All you have to do is select the specific dictionary you want LinguistX to use. This also helps you make more precise queries and find what you're looking for through a word's deep meaning, not just its surface form.
Taggers decide parts of speech.
To tag a word properly means examining its context a little in the surrounding text. Obviously the extent of context examination must be as small as possible to preserve speed but wide enough to do the job. LinguistX especially shines in handling phrases. But LinguistX can tell that you are looking for exceptional batting performances in baseball. All this has come out of years of linguistic research, turned into practical software.