Boolean Retrieval

Boolean Retrieval

Boolean Retrieval is a retrieval model where documents are represented as sets of terms, and queries are expressed as Boolean expressions of terms using operators like AND, OR, and NOT.

Mechanism

• Input: A query like (Brutus AND Caesar) AND NOT Cassius.
• Representation: Often visualized using a Term-Document Incidence Matrix, where rows represent terms and columns represent documents (1 if present, 0 if absent).
• Processing: The system performs bitwise operations on the incidence vectors (or more commonly, intersects posting lists in an Inverted Index).

Match vs. Rank

In Boolean Retrieval, there is no “ranking.” A document either matches the boolean condition (stays in the result set) or it doesn’t. There is no concept of a document being “more relevant” than another.

Pros and Cons

Pros	Cons
Precise control for expert users	No relevance ranking (all or nothing)
predictable and transparent results	”Feast or famine”: too many or zero results
Efficient technical implementation	Difficult for non-expert users to write queries

Connections

• Data Structure: Usually implemented via an Inverted Index.
• Evolution: Succeeded by ranked retrieval models like Vector Space Model and BM25.
• Operations: Uses Tokenization and Stemming to normalize terms before matching.

Appears In

• IR-L02 - Indexing and Boolean Retrieval