WikiBrain

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Advanced Semantic Relatedness Usage

WikiBrain provides a robust suite of SR measures and tools. By default, when you load some language editions, Wikipedia trains the Milne Witten [2006] SR measure. This algorithm strikes an excellent balance between accuracy, speed, and coverage. However, you may tap into a variety of other algorithms.

Modes of operation

As described in the SR overview page, WikiBrain supports a variety of modes of operation. The two key dimensions it supports are:

  • Method:
    • mostSimilar(A): finds the most similar concepts for a particular query A.
    • similarity(A, B): estimates the similarity of concepts A and B.
    • cosimilarity(rows, cols): builds a cosimilarity matrix between the concept in rows and `cols.
  • Query mode:
    • phrase: Concepts are represented by free-text queries.
    • article: Concepts are represented by Wikipedia article via their id.

SR researchers have traditionally studied the similarity / phrase cell in this six cell (two by three) grid. However, WikiBrain suports all six cells. In fact, in our experience applications are more likely to need cosimilarity and mostSimilar than similarity.

Efficiency

There are two dimensions of efficiency an application needs to consider. Training complexity describes the amount of CPU time needed to create the data needed by an SR measure. It is incurred once, offline, before an application is launched. Online complexity describes the amount of CPU time needed to perform an API. This cost is incurred for every invocation of an SR API call. There is often a tradeoff between online and training complexity. Many algorithms that perform quickly and accurately reuqire longer training time.

One important example of the training vs online complexity tradeoff is in precomputing feature matrices for articles. Many SR measures can precompute feature matrices for all articles in a language. In doing so, a user pays a training penalty in exchange for runtime performance. For SR measures that support them, feature matrices are built by default when a user runs the SRBuilder in mostSimilar mode (next section).

One additional note about online complexity: For most algorithms the cosimilarity() method on m rows and n columns runs much more quickly than m * n calls to similarity().

Summary of Algorithmic Tradeoffs

The table below summarizes the most commonly used SR measures in WikiBrain and the tradeoffs between them.

Metric Data used Accuracy Training complexity Runtime complexity Has feature matrix
ESA text med-high slow slow yes
ensemble ensemble high slow slow no
milnewitten links med-high fast fast yes
category category low fast fast no
word2vec text med-high high low yes

Running the SR builder

To use these algorithms, you must build models that capture the statistical relationships an SR metric uses to calculate similarities. To do this, run the SRBuilder java program for a particular SR metric (in this case the ensemble metric). You can also use your IDE or the "override command line" feature of the GUILoader to run the builder.

./wb-java.sh org.wikibrain.sr.SRBuilder -l simple -m ensemble -o both

The above example shows the three key arguments for running the SR builder. The -l argument specifies the langauge of the SR metric you want to build. The -m argument specifies the name of the metric (from the table above). The -o argument specifies the mode. It can be similarity, cosimilarity, or both. If both is specified, feature matrices will be constructed if the SR measure supports them (see efficiency, above.)

Normalizers

Each SR measure produces estiamted SR values on an arbitrary scale. To make the values more interpretable, WikiBrain offers a variety of normalizers that translate estimated values to a consistent scale. Most SR measures use the percentile normalizer, which converts all values to percentiles on a 0 to 1.0 scale. Many more normalizers are available in the org.wikibrain.sr.normalize package. You can override a particular metric's normalizer by specifying something like the following in your configuration file:

sr.metric.local.milnewitten.similaritynormalizer : loess
sr.metric.local.milnewitten.mostsimilarnormalizer : loess

Be aware that you must rebuild your SR metric after changing the normalizer.

SR Algorithms

ESA SR Measure

An optimized implementation of Gabrilovich and Markovitch's Explicit Semantic Analysis SR measure. The ESA measure represents a query concept as a sparse "concept vector" that includes the Wikipedia articles most related to the query. It is reasonably accurate, but relatively slow - particularly for model training. Reference: Gabrilovich, Evgeniy, and Shaul Markovitch. "Computing Semantic Relatedness Using Wikipedia-based Explicit Semantic Analysis." IJCAI. Vol. 7. 2007.

MilneWitten SR Measure

The Milne / Witten SR measure calculates the overlap between the inlinks and outlinks of the query concept(s). It is reasonably fast and accurate. It works particularly well for mostSimilar queries. Reference: Witten, I., and David Milne. "An effective, low-cost measure of semantic relatedness obtained from Wikipedia links." Proceeding of AAAI Workshop on Wikipedia and Artificial Intelligence: an Evolving Synergy, AAAI Press, Chicago, USA. 2008.

Category SR Measure

The category SR measure implements a version of Strube and Ponzetti's WikiRelate SR measure. It is relatively inaccurate, but very fast, and useful for it's descriptive power and added value to the ensemble (below). This measure examines the category structure of Wikipedia (a directory graph) and finds the distance to the lowest common subsumer category. While the original paper Reference: Strube, Michael, and Simone Paolo Ponzetto. "WikiRelate! Computing semantic relatedness using Wikipedia." AAAI. Vol. 6. 2006.

Ensemble SR Measure
Word2Vec SR Measure