Query Expansion

Query expansion involves taking documents judged relevant by the user as the basis for a new search to find others which are similar. Words and phrases are extracted from relevant documents and weighted to generate an expanded query. Early evaluations of this facility [3] showed that it was effective for finding documents covering the same topics as those the user had already chosen.

Recent Okapi studies have examined the way in which users perceive query expansion and how the interface should best be designed to present it to them. Comparisons have been made between two forms of query expansion: automatic and interactive.

• In automatic query expansion, all the terms extracted from relevant documents are used to produce a new document set. The user never sees the terms and therefore has no control over how the expansion operates.

• In interactive query expansion, the system extracts terms from relevant documents and presents them to the user who decides which of them to include in the expanded search.

The ENQUIRE project introduced a third alternative: incremental query expansion, which is discussed in later chapters.

• Automatic Expansion: The VT100 Interface
• Interactive Expansion: The XOkapi GUI