# Efficient Inference Methods for Probabilistic Logical Models

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Efficient Inference Methods for Probabilistic Logical Models
Sriraam Natarajan Dept of Computer Science, University of Wisconsin-Madison

Take-Away Message Inference in SRL Models is very hard!!!!
This talk – Presents 3 different yet related inference methods The methods are independent of the underlying formalism They have been applied to different kinds of problems

Propositional Model! The World is inherently Uncertain
Graphical Models (here e.g. a Bayesian network) - Model uncertainty explicitly by representing the joint distribution Fever Ache Random Variables Influenza Direct Influences Propositional Model!

Real-World Data (Dramatically Simplified)
Non- i.i.d PatientID Date Physician Symptoms Diagnosis P /1/ Smith palpitations hypoglycemic P /1/ Jones fever, aches influenza PatientID Gender Birthdate P M /22/63 Shared Parameters Solution: First-Order Logic / Relational Databases PatientID Date Lab Test Result PatientID SNP1 SNP2 … SNP500K P AA AB BB P AB BB AA P /1/01 blood glucose P /9/01 blood glucose Multi-Relational PatientID Date Prescribed Date Filled Physician Medication Dose Duration P /17/ /18/ Jones prilosec mg 3 months

Statistical Relational Learning (SRL)
Logic + Probability = Probabilistic Logic aka Statistical Relational Learning Models Logic Statistical Relational Learning (SRL) Add Probabilities Probabilities Add Relations Uncertainty in SRL Models is captured by probabilities, weights or potential functions

Alphabetic Soup => Endless Possibilities
Probabilistic Relational Models (PRM) Bayesian Logic Programs (BLP) PRISM Stochastic Logic Programs (SLP) Independent Choice Logic (ICL) Markov Logic Networks (MLN) Relational Markov Nets (RMN) CLP-BN Relational Bayes Nets (RBN) Probabilistic Logic Progam (PLP) ProbLog …. Web data (web) Biological data (bio) Social Network Analysis (soc) Bibliographic data (cite) Epidimiological data (epi) Communication data (comm) Customer networks (cust) Collaborative filtering problems (cf) Trust networks (trust) Fall 2003– OSU, Spring 2004 UW, Spring Purdue, Fall 2008 – CMU

Key Problem - Inference
Equivalent to counting 3SAT Models => #P-complete More pronounced in SRL Models Prohibitively large number of Objects and Relations Inference has been the biggest bottleneck for the use of SRL Models in practice

Grounding / Propositionalization

Realistic Example – Gene-fold Prediction
Thanks to Irene Ong

Recent Advances in SRL Inference
Preprocessing for Inference FROG – Shavlik & Natarajan (2009) Lifted Exact Inference Lifted Variable Elimination – Poole (2003), Braz et al(2005) Milch et al (2008) Lifted VE + Aggregation – Kisynski & Poole (2009) Sampling Methods MCMC techniques – Milch & Russell (2006) Logical Particle Filter – Natarajan et al (2008), ZettleMoyer et al (2007) Lazy Inference – Poon et al (2008) Approximate Methods Lifted First-Order Belief Propagation – Singla & Domingos (2008) Counting Belief Propagation – Kersting et al (2009) MAP Inference – Riedel (2008) Bounds Propagation Anytime Belief Propagation – Braz et al (2009)

Fast Reduction of Grounded MLNs
Counting Belief Propagation Anytime Lifted Belief Propagation Conclusion

Fast Reduction of Grounded MLNs
Counting Belief Propagation Anytime Lifted Belief Propagation Conclusion

Markov Logic Networks Weighted logic
Standard approach 1) Assume finite number of constants 2) Create all possible groundings 3) Perform statistical inference (often via sampling) Weight of formula i No. of true groundings of formula i in x (Richardson & Domingos, MLJ 2005)

Counting Satisfied Groundings
Typically lots of redundancy in FOL sentences  x, y, z p(x) ⋀ q(x, y, z) ⋀ r(z)  w(x, y, z) If p(John) = false, then formula = true for all Y and Z values

Factoring Out the Evidence
Let A = weighted sum of formula satisfied by evidence Let Bi = weighted sum of formula in world i not satisfied by evidence Prob(world i ) = e Bi e B … + e Bn e A + Bi e A + B … + e A + Bn

Take-Away Message - I Efficiently factor out those formula groundings that evidence satisfies Can potentially eliminate the need for approximate inference

Worked Example 1012 The Evidence
 x, y, z GradStudent(x) ⋀ Prof(y) ⋀ Prof(z) ⋀ TA(x, z) ⋀ SameGroup(y, z)  AdvisedBy(x, y) 10,000 People at some school 2000 Graduate students 1000 Professors 1000 TAs 500 Pairs of professors in the same group The Evidence Total Num of Groundings = |x|  |y|  |z| = 1012 1012

GradStudent(x) FROG keeps only these X values 2000 Grad Students 8000

Prof(y) 1000 Professors 9000 Others 2 × 1011 2 × 1010
GradStudent(x) ⋀ Prof(y) ⋀ Prof(z) ⋀ TA(x,z) ⋀ SameGroup(y,z)  AdvisedBy(x,y) 1000 Professors Prof(P2) Prof(y) True ¬ Prof(P1) Prof(P2) 9000 Others False ¬ Prof(P1) 2 × 1011 2 × 1010

<<< Same as Prof(y) >>>
GradStudent(x) ⋀ Prof(y) ⋀ Prof(z) ⋀ TA(x,z) ⋀ SameGroup(y,z)  AdvisedBy(x,y) <<< Same as Prof(y) >>> 2 × 1010 2 × 109

1000 true SameGroup’s SameGroup(y, z) 106 – 1000 Others 2 × 109
GradStudent(x) ⋀ Prof(y) ⋀ Prof(z) ⋀ TA(x,z) ⋀ SameGroup(y,z)  AdvisedBy(x,y) SameGroup(P1, P2) 1000 true SameGroup’s SameGroup(y, z) True 106 Combinations 106 – Others ¬ SameGroup(P2, P5) False 2000 values of X 1000 Y:Z combinations 2 × 109 2 × 106

GradStudent(x) ⋀ Prof(y) ⋀ Prof(z) ⋀ TA(x,z) ⋀ SameGroup(y,z)  AdvisedBy(x,y)
1000 TA’s TA(P7,P5) TA(x, z) True 2 × 106 Combinations 2 × 106 – 1000 Others ¬ TA(P8,P4) False ≤ values of X ≤ Y:Z combinations ≤ 106

Original number of groundings = 1012
GradStudent(x) ⋀ Prof(y) ⋀ Prof(z) ⋀ TA(x,z) ⋀ SameGroup(y,z)  AdvisedBy(x,y) 1012 Original number of groundings = 1012 106 Final number of groundings ≤ 106

Sample Results: UWash-CSE
Fully Grounded Net FROG’s Reduced Net FROG’s Reduced Net without One Challenging Rule advisedBy(x,y)  advisedBy(x,z)  samePerson(y,z))

Fast Reduction of Grounded MLNs
Counting Belief Propagation Anytime Lifted Belief Propagation Conclusion

Belief Propagation Message passing algorithm – Inference on graphical models For factor graphs Exact – if the factor graph is a tree Approximate when it has cycles Loopy BP does not guarantee convergence, but is found to be very useful in practice X3 f1 X1 f2 X2

Belief Propagation Identical Factors

Take-Away Message – II Counting shared factors can result in great efficiency gains for (loopy) belief propagation

Counting Belief Propagation
Two Steps Compress Factor Graph Run modified BP

Step 1: Compression

Step 2: Modified Belief Propagation

Factored Frontier (FF)
Probabilistic inference over time is central to many AI problems In contrast to static domains, we need approximation Variables easily become correlated over time by virtue of sharing common influences in the past Factored Frontier [Murphy and Weiss 01] Unroll DBN Run (loopy) BP Lifted First-Order FF: Use CBP in place of BP

Lifted First-order Factored Frontier
Successor fluent 20 people over 10 time steps Max number of friends 5 Cancer never observed Time step randomly selected

Fast Reduction of Grounded MLNs
Counting Belief Propagation Anytime Lifted Belief Propagation Conclusion

The Need for Shattering
Lifted BP depends on clusters of variables being symmetric, that is, sending and receiving identical messages In other words, it is about dividing random variables in cases – called as “shattering”

Intuition for Anytime Lifted BP
in(House, Town) next(House,Another) earthquake(Town) Alarm can go off due to an earthquake lives(Another,Neighbor) alarm(House) saw(Neighbor,Someone) burglary(House) masked(Someone) A “prior” factor makes alarm going off unlikely without those causes Alarm can go off due to burglary partOf(Entrance,House) in(House,Item) broken(Entrance) missing(Item)

Intuition for Anytime Lifted BP
alarm(House) earthquake(Town) in(House, Town) burglary(House) next(House,Another) lives(Another,Neighbor) saw(Neighbor,Someone) masked(Someone) in(House,Item) missing(Item) partOf(Entrance,House) broken(Entrance) Given a home in sf with home2 and home3 next to it with neighbors jim and mary, each seeing person1 and person2, several items in home, including a missing ring and non-missing cash, broken front but not broken back entrances to home, an earthquake in sf, what is the probability that home’s alarm goes off?

Lifted Belief Propagation
Model for house ≠ home and town ≠ sf not shown Message passing over entire model before obtaining query answer next(home,home2) in(home, sf) Complete shattering before belief propagation starts lives(home2,jim) earthquake(sf) saw(jim,person1) masked(person1) next(home,home3) alarm(home) lives(home2,mary) saw(mary,person2) burglary(home) masked(person2) in(home,cash) partOf(front,home) missing(cash) broken(front) in(home,Item) in(home,ring) partOf(back,home) Item not in { ring,cash,…} missing(ring) missing(Item) broken(back)

Intuition for Anytime Lifted BP
next(home,home2) Evidence in(home, sf) lives(home2,jim) earthquake(sf) saw(jim,person1) Given earthquake, we already have a good lower bound, regardless of burglary branch Query masked(person1) next(home,home3) alarm(home) lives(home2,mary) saw(mary,person2) burglary(home) Wasted shattering! Wasted shattering! Wasted shattering! Wasted shattering! Wasted shattering! masked(person2) in(home,cash) partOf(front,home) missing(cash) broken(front) in(home,Item) in(home,ring) partOf(back,home) Item not in { ring,cash,…} missing(ring) missing(Item) broken(back)

Using only a portion of a model
By using only a portion, we don’t have to shatter other parts of the model How can we use only a portion? A solution for propositional models already exists: box propagation (Mooij & Kappen NIPS ‘08)

Box Propagation A way of getting bounds on query without examining entire network. [0, 1] A

Box Propagation A way of getting bounds on query without examining entire network. [0.36, 0.67] [0, 1] A B f1

Box Propagation A way of getting bounds on query without examining entire network. [0,1] [0.1, 0.6] [0.38, 0.50] [0.05, 0.5] f2 ... A B f1 [0,1] f3 ... [0.32, 0.4]

Box Propagation A way of getting bounds on query without examining entire network. [0.2,0.8] [0.3, 0.4] [0.41, 0.44] [0.17, 0.3] f2 ... A B f1 [0,1] f3 ... [0.32, 0.4]

Box Propagation A way of getting bounds on query without examining entire network. 0.45 0.32 0.42 0.21 f2 ... A B f1 0.3 f3 ... 0.36 Convergence after all messages are collected

Take-Away Message - III
Anytime BP = Incremental Shattering + Box Propagation

Anytime Lifted Belief Propagation
Start from query alone [0,1] alarm(home) The algorithm works by picking a cluster variable and including the factors in its blanket

Anytime Lifted Belief Propagation
in(home, Town) earthquake(Town) [0.1, 0.9] alarm(home) burglary(home) (alarm(home), in(home,Town), earthquake(Town)) after unifying alarm(home) and alarm(House) in (alarm(House), in(House,Town), earthquake(Town)) producing constraint House = home Again, through unification Blanket factors alone can determine a bound on query

Anytime Lifted Belief Propagation
(in(home, sf)) in(home, sf) earthquake(sf) Cluster in(home, Town) unifies with in(home, sf) in (in(home, sf)) (which represents evidence) splitting cluster around Town = sf [0.1, 0.9] alarm(home) burglary(home) in(home, Town) Bound remains the same because we still haven’t considered evidence on earthquakes Town ≠ sf earthquake(Town)

Anytime Lifted Belief Propagation
in(home, sf) (earthquake(sf)) represents the evidence that there was an earthquake earthquake(sf) [0.8, 0.9] alarm(home) burglary(home) Now query bound becomes narrow No need to further expand (and shatter) other branches If bound is good enough, there is no need to further expand (and shatter) other branches in(home, Town) Town ≠ sf earthquake(Town)

Anytime Lifted Belief Propagation
in(home, sf) earthquake(sf) [0.85, 0.9] partOf(front,home) alarm(home) burglary(home) broken(front) in(home, Town) We can keep expanding at will for narrower bounds… Now query bound becomes narrow Town ≠ sf earthquake(Town)

Anytime Lifted Belief Propagation
next(home,home2) in(home, sf) … until convergence, if desired. lives(home2,jim) earthquake(sf) saw(jim,person1) 0.8725 masked(person1) next(home,home3) alarm(home) lives(home2,mary) saw(mary,person2) burglary(home) masked(person2) in(home,cash) partOf(front,home) missing(cash) broken(front) in(home,Item) in(home,ring) partOf(back,home) Item not in { ring,cash,…} missing(ring) missing(Item) broken(back)

Connection to Resolution Refutation
Incremental shattering corresponds to building a proof tree in(home, sf) earthquake(sf) true alarm(home) burglary(home) in(home,L), L not in {sf} earthquake(L), L not in {sf}

Fast Reduction of Grounded MLNs
Counting Belief Propagation Anytime Lifted Belief Propagation Conclusion

Conclusion Inference is the key issue in several SRL formalisms
FROG - Keeps the count of unsatisfied groundings Order of Magnitude reduction in number of groundings Compares favorably to Alchemy in different domains Counting BP - BP + grouping nodes sending and receiving identical messages Conceptually easy, scaleable BP algorithm Applications to challenging AI tasks Anytime BP – Incremental Shattering + Box Propagation Only the most necessary fraction of model considered and shattered Status – Implementation and evaluation

Conclusion Algorithms are independent of representation
Variety of Applications Parameter Learning of Relational Models Social Networks Object Recognition Link Prediction Activity Recognition Model Counting Bio-Medical Applications Relational RL

Future Work FROG CBP Anytime BP SRL Models
Combine with Lifted Inference Exploit commonality across rules CBP Integrate with Parameter Learning in SRL Models Extend to Multi-Agent RL, Lifted Pairwise BP Anytime BP Heuristic to expand the network Understand closer connections to Resolution SRL Models Learning Dynamic SRL Models Structure Learning remains an open issue

Acknowledgements* Babak Ahmadi - Fraunhofer Institute
Rodrigo de Salvo Braz – SRI International Hung Bui – SRI International Vitor Santos Costa – U Porto Kristian Kersting - Fraunhofer Institute Gautam Kunapuli – UW Madison David Page – UW Madison Stuart Russell – UC Berkeley Jude Shavlik – UW Madison Prasad Tadepalli – Oregon State University * Ordered by Last name

Thanks!

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