Query Modifier's Disjunctify Parse Strategy
Some users are not careful in how they perform searches. For example, they may use synonyms to try to cast a "broad net", for example:
tractor repair manual guide documentation
Watson™ Explorer Engine assumes that users carefully choose their search terms. Consequently, it uses AND logic for each term the user types in. Consequently, if a document does not contain every term that a user entered, that document will not be returned as a match. And because most documents are unlikely to contain every search term, the search above may return very few or zero documents.
The disjunctify feature makes the query use OR logic. As a result, documents that mostly match the user's query will be returned. The number of terms required for disjunctification to occur is configurable. See Configuring the Query Modifier for details.