Crosspartition Clustering: - PowerPoint PPT Presentation

Title: Crosspartition Clustering:


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Cross-partition Clustering
Revealing Analogous Themes across Related Topics
Zvika Marx, Ido Dagan, Eli Shamir
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Outline

• Motivation identifying analogies /
  correspondences across different domains a
  fascinating aspect of intelligence !
• Computational framework revealing concepts /
  themes through Word Clustering
• Probabilistic clustering the Information
  Distortion / Information Bottleneck methods
• The Cross Partition Clustering Method
• Algorithm and underlying principles
• Application to cross-religion comparison

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What is Analogy?

• Non-obvious similarity or correspondence
• Principled, deep, systematic relation (in
  contrast to mere appearance)
• Analogies are discovered or revealed
• related with problem solving
• require insight, creativity, fluid thinking
• Concept formation , Feature selection ?

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Example Orchestra and Army
General
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Cross-partition Clustering Setting

• Given data pre-partitioned to distinct subsets
  w1,, wN, N ? 2
• Goal revealing themes that cut across all subsets

Subset w1
Subset w2
Subset wN

• soft (probabilistic) assignments
• (the formalism may even allows soft
  pre-partitioning)

partition
partition
partition
Previous works Dagan, Marx Shamir, CoNLL
2002 Marx, Dagan Shamir, NIPS 2003
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Background Probabilistic Clustering

• Input
• for each x?X (clustered element) relative freq
  p(x)
• for each x and each y?Y (feature)
• conditional occurrence probability p(yx)
• Output
• for each x and each cluster c assignment
  probability p(cx)
• ( and for each c, distribution over the y's
  p(yc) a centroid representation of c
  in the feature space )

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Prob. Clustering Iterative Loop

• K-means style iterative loop
• (1) Recalculate assignment probabilities pt(cx)
  
• pt(cx) ? pt-1(c) exp ??KLp(yx)pt?1(yc)
  
• exponentially inverse to KL divergence between
  the representative feature distributions of x and
  c
• (2) Recalculate cluster centroids pt(yc) for
  each cluster c
• pt(yc) ? ?x p(x) pt(cx) p(yx)

t
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Information Distortion / Bottleneck

• Data clustering interpreted as a means for
  conveying the relevant information in the data
• It maximizes information the clusters provide
  about whats relevant (i.e. the feature variable
  Y)
• Subject to the above, minimize the information
  provided by the data about the clusters ? Maximum
  Entropy
• Optimization problem
• argmin H(C) ? H(CX) ? H(YC)
• The optional H(C) differentiate IB (with) from
  ID (without)
• The K-means iterative steps are derived from
  this term

over all p(c), p(cx), p(yc) distributions
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ID/IB Convergence

• The minimized term H(C) ? H(CX) ? H(YC)
  is bounded
• Each iterative loop reduces its value (at time t)
  by KL pt(c) pt-1(c)
• ?x p(x) KL pt-1(cx) pt(cx)
• ? ?c pt(c) KL pt(yc) pt-1(yc) gt 0
• ? convergence to a configuration of distributions
  that (locally) minimizes the term

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CP Clustering Setting (reminder)

• Data pre-partitioned to w1,, wN, N ? 2
• Goal revealing, themes that cut across all
  subsets

Subset w1
Subset w2
Subset wN

• soft (probabilistic) assignments
• (the formalism may also allow soft
  pre-partitioning)

partition
partition
partition
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Cross-partition Clustering

• Input additional to p(x), p(yx)
• for each x and each w?W (pre-given subset)
• prob. of assignment to pre-given subset p(wx)
• In principle, p(wx) can be any prob. dist. over
  W in our experiments 0/1 hard partitioning
• Output
• p(cx) (as in any probabilistic clustering)
• A novel aspect re-associating (re-assigning)
  features to clusters p(cy)
• Two types of centroids p(yc,w), p(yc)

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The Cross Partition Algorithm

• (1) Assignment probability p(cx) (as in IB/ID)
• pt (cx) ? exp ??KLp(yx)pt?1(yc)
• (2) Recalculate w-projected local centroids
• pt (yc,w) ? ?x p(x) pt (cx) p(yx) p(wx)
• (3) Re-associate feature with clusters
• pt (cy) ? ?w pt (yc,w)?p(w)
• (4) Biased centroids, based on the above
• pt (yc) ? pt (cy) p(y)

t
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Cross-partition Principles

• Assignments p(cx) as in IB/ID (relying on MaxEnt
  principle)
• Look for C that, jointly with W, is informative
  about Y distribution
• ? local centroids p(yc,w)
• Re-associate features with clusters, p(cy),
  so that the associations are independent of W
• (again relying on MaxEnt principle)

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4 Different Terms to Optimize
(1) FCP1 ? H(C) ? H(CX) ? H(YC)
H(YC) ? ? ?x p(x) ?c p(cx) ?y p(yx) log
p(yc) (2) FCP2 H(YC,W) ( assuming
I(CYWX) 0 ) ? ? ?x p(x) ?c p(cx) ?y
p(yx) ?w p(wx) log p(yc,w) (3) FCP3 ?
H(C) ? H(CY) ? H(YC,W) H(CY)
? ?y p(y) ?c p(cy) log p(cy) H(YC,W)
? ? ?w p(w) ?y p(y) ?c p(cy) log p(yc,w)
(4) FCP4 H(YC) ? ? ?y p(y) ?c p(cy)
log p(yc)
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Dynamics ID/IB versus CP
Information Distortion
Cross Partition
? H(CX)
? H(CX)
H(YC,W)
H(YC)
H(YC)
? H(CY)
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Priored and Unpriored Variants

• As in the IB method, it is possible to add prior
  in the iterative cycle update steps (depending on
  the exact terms being optimized)
• - In step (1)
• pt(cx) ? pt?1(c) exp
  ??KLp(yx)pt?1(yc)
• - In step (3)
• pt(cy) ? pt (c) ?w pt?1(yc,w)?p(w)
• So there are four variants of the CP method
  (withwithout prior in step (1)(3) )
• The previous works mentioned before (CoNLL2002,
  NIPS2004) in fact implement two of these variants

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Religion Data

• Given 5 corpora focused on religions
  Buddhism, Christianity, Hinduism, Islam and
  Judaism.
• Encyclopedic entries, online magazines,
  introductory web articles.
• Co-occurrence statistics
• 200 (auto extracted) keywords of each religion
  (same word appearing in two corpora is taken as
  two distinct elements)
• Count feature words (7000) in an undirected ?5
  window truncated by sentence boundaries.

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Clusters Reveal Meaningful Themes

• Two Clusters spiritual vs. establishment
  aspects
• Seven Clusters (our titles, highest p(cy)
  features that did not have a dual role of
  clustered keywords)
• schools central, dominant?, mainstream,
  affiliate
• divinity omnipotent?, almighty, mercy,
  infinite
• religious experience intrinsic, mental,
  realm, mature
• writings commentary, manuscript, dictionary,
  grammar
• festivals and rite annual, funeral,
  rebuild, feast
• sin and suffering vegetable, insect,
  penalty, quench
• community and family parent, nursing,
  spouse, elderly
• Interesting correspondence to classical comp.
  religion work dimensions of the scared (Smart,
  1999)
• ritual, mythic, experiential/emotional, ethical,
  social, material

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Evaluation

• Measure how well the output clusters capture
  expert clusters, of freely chosen keywords.
• We have not instructed the experts on how to
  choose the words.
• Three experts participated each one of them
  covered a different subset of all possible
  religion comparisons.

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Example Good Match to Expert

• Our sacred writings cross-partition cluster
• terms used by the expert are underlined
• first 15 words per religion shown (p(cx)
  indicated)
• Corresponding expert cluster ( hit scores
  high in another cluster)

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Example Poor Match to Expert

• Our suffer, sin and punishment CP cluster
• The mysticism expert cluster was most closely
  relevant

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Quantitative Evaluation

• Comparing religion pairs (W 2) hard
  clustering
• Evaluation restricted to terms common to two
  experts
• Jaccard coefficient proportion between
• num. of pairs of words co-assigned to the same
  cluster (no matter which) by both expert and
  algorithm
• A num. of pairs co-assigned by one but not by
  the other

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Conclusion

• Focus on particular features ones that are
  important in the context of identifying
  commonalities across domains
• Applicable to real-world data
• Principled info-theoretic approach
• For future work
• Detect relational structure
• Problem solving
• More applications Commercial products, Legal

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Thank You

• Time
• - Last session
• Patience
• (Last session!)