Boolean operators are hard for users to understand:
"Give me all documents on Unix and MS DOS" actually means:
"Give me all documents that are about Unix or about MS DOS"
- Most systems only support one operator at a time: either and
all words, meaning "match all keywords", or or all words,
meaning "match any keyword".
- Each word corresponds to a set of documents. Logical operators are
translated into set operators. (and is set intersection,
or is set union)
- Few systems support negation: finding documents not containing
certain words or phrases. This helps eliminate the wrong documents
for words that have several meanings depending on the context.
