Archive for the ‘Implicit Associations’ Category

Semantic Vectors

Tuesday, August 16th, 2011

Semantic Vectors

From the webpage:

Semantic Vector indexes, created by applying a Random Projection algorithm to term-document matrices created using Apache Lucene. The package was created as part of a project by the University of Pittsburgh Office of Technology Management, and is now developed and maintained by contributors from the University of Texas, Queensland University of Technology, the Austrian Research Institute for Artificial Intelligence, Google Inc., and other institutions and individuals.

The package creates a WordSpace model, of the kind developed by Stanford University’s Infomap Project and other researchers during the 1990s and early 2000s. Such models are designed to represent words and documents in terms of underlying concepts, and as such can be used for many semantic (concept-aware) matching tasks such as automatic thesaurus generation, knowledge representation, and concept matching.

The Semantic Vectors package uses a Random Projection algorithm, a form of automatic semantic analysis. Other methods supported by the package include Latent Semantic Analysis (LSA) and Reflective Random Indexing. Unlike many other methods, Random Projection does not rely on the use of computationally intensive matrix decomposition algorithms like Singular Value Decomposition (SVD). This makes Random Projection a much more scalable technique in practice. Our application of Random Projection for Natural Language Processing (NLP) is descended from Pentti Kanerva’s work on Sparse Distributed Memory, which in semantic analysis and text mining, this method has also been called Random Indexing. A growing number of researchers have applied Random Projection to NLP tasks, demonstrating:

  • Semantic performance comparable with other forms of Latent Semantic Analysis.
  • Significant computational performance advantages in creating and maintaining models.

So, after reading about random indexing, etc., you can take those techniques out for a spin. It doesn’t get any better than that!

Reflective Random Indexing and indirect inference…

Tuesday, August 16th, 2011

Reflective Random Indexing and indirect inference: A scalable method for discovery of implicit connections by Trevor Cohen, Roger Schvaneveldt, Dominic Widdows.

Abstract:

The discovery of implicit connections between terms that do not occur together in any scientific document underlies the model of literature-based knowledge discovery first proposed by Swanson. Corpus-derived statistical models of semantic distance such as Latent Semantic Analysis (LSA) have been evaluated previously as methods for the discovery of such implicit connections. However, LSA in particular is dependent on a computationally demanding method of dimension reduction as a means to obtain meaningful indirect inference, limiting its ability to scale to large text corpora. In this paper, we evaluate the ability of Random Indexing (RI), a scalable distributional model of word associations, to draw meaningful implicit relationships between terms in general and biomedical language. Proponents of this method have achieved comparable performance to LSA on several cognitive tasks while using a simpler and less computationally demanding method of dimension reduction than LSA employs. In this paper, we demonstrate that the original implementation of RI is ineffective at inferring meaningful indirect connections, and evaluate Reflective Random Indexing (RRI), an iterative variant of the method that is better able to perform indirect inference. RRI is shown to lead to more clearly related indirect connections and to outperform existing RI implementations in the prediction of future direct co-occurrence in the MEDLINE corpus.

The term “direct inference” is used for establishing a relationship between terms with a shared “bridging” term. That is the terms don’t co-occur in a text but share a third term that occurs in both texts. “Indirect inference,” that is finding terms with no shared “bridging” term is the focus of this paper.

BTW, if you don’t have access to the Journal of Biomedical Informatics version, try the draft: Reflective Random Indexing and indirect inference: A scalable method for discovery of implicit connections