|
Vector space model (or term vector model) is an algebraic model used for information filtering, information retrieval, indexing and relevancy rankings. It represents natural language documents in a formal manner by the use of vectors in a multi-dimensional space based on an origin. It was used for the first time by the SMART Information Retrieval System. Vectors consist of lengths (magnitudes) and direction (angles). (See vectors). The basic theory proposed in the vector space model was to view the term (or keyword) query (Q) and the documents (D(n)) in which the terms were found as vectors. Relevancy rankings of documents in keyword search could be calculated using the vector theory model based on how large a deviation the angles (based on the cosine of these angles) of each document vector were in relation to the original query vector based on the scalar product between the query vector and the document vector and the assumptions of the document similarities theory. Thus a cosine value of zero meant that the query and document vector were orthogonal to each other and meant that there was no match or the term simply did not exist in the document being considered. The classic vector space model as proposed by Salton, Wong and Yang had both local and global parameters incorporated in the term weight (w(n)) equation (known as the tf-idf): w(n) = f(n) x Log (D / d(n)) where: Note that the quotient, d(n)/D, is essentially the probability of finding the document containing the term n, in the document set being used and represents the global parameter (compare with term count model below which only considered local parameters.
Assumptions and Limitations of The Vector Space Model The Vector Space Model has the following limitations: Comparison with The Term Count Model The alternative Term Count Model, an earlier model, only considered local parameters and did not account for global parameters. See the separate section on Term Count Model in Wikipedia. Models based on and extending the vector space model Models based on and extending the vector space model include: Further reading See also | ||||||||
|
| |||||||||
 |
|
| |