RuleML2015: Using PSL to Extend and Evaluate Event Ontologies

Using PSL to Extend and Evaluate Event Ontologies

Megan Katsumi and Michael Gruninger

Semantic Technologies LabUniversity of Toronto

Ninth International Web Rule SymposiumAugust 2-5, 2015

Katsumi, Gruninger (Semantic Technologies Lab) University of Toronto (MIE) RuleML 2015 1 / 37

An Opportunity for CEP

Events on the Semantic Web

Unsurprisingly, a popular topic

Many event ontologies for the Semantic Web have been developed

Is this an opportunity for Complex Event Processing?

Can we reuse Semantic Web Event Ontologies to support Complex EventProcessing?


Event Ontologies on the Semantic Web

Some examples:

The Simple Event Model (SEM): interoperability with event information onthe web

Linked Open Descriptions of Events (LODE): aims to integrate eventinformation between ontologies

The Event Ontology: no specific application

Applications tend to focus on integration of event information.


Why Bother?

If Semantic Web event ontologies can support CEP

We can reason about the event data that has and will be integrated withthese ontologies

Other CEP approaches can benefit similarly by incorporating these ontologiesinto their design

More opportunities for CEP applications


Complex Event Processing with Competency Questions

How to evaluate whether the ontologies can support the desired CEP applications?

Competency Questions (CQs): queries used to evaluate the reasoning abilityof a theory

Evaluated as an entailment problem: T ∪ Σ |= CQ

If the CQ is entailed, then the semantics and signature of the theory aresufficient!


CEP Queries

A Sample of the Queries Used:

CQ2 What can possibly occur next after an occurrence of some activity?

CQ3 Are occurrences of two activities possibly subactivity occurrences ofthe same complex activity occurrence?

CQ4 Are any other activities possibly taking place at the same place andthe same time as a particular activity?

CQ5 Assuming that occurrences of two activities are part of the sameoverall activity occurrence, what activities possibly occurredbetween them?

CQ6 What activity could have occurred before an occurrence of someother observed activity?

CQ7 Is there an activity that will definitely occur after an occurrence ofsome activity?


CEP Results

How did they do?

All ontologies failed to answer any of the queries

Not surprising

Event Ontologies were designed for integration, not CEP applicationsGenerally, Semantic Web ontologies known to have reasoning limitations


Now What?

Can we reuse Semantic Web Event Ontologies to support Complex EventProcessing?

Doesn’t look like it

The end?


Now What?

But seriously...

Consider:

What caused these failures?

Can anything be done?

Recall, T ∪ Σ |= CQ

Entailment requires the ontologies to have sufficient signature and semantics.


Issues Identified

2 Types of Causes Observed:

1 Depth of Scope All ontologies failed to answer any CQs in scope

2 Breadth of Scope All but 4 of the 13 queries were out of scope for all 3Semantic Web Event Ontologies


Issues Identified

Each requires a different solution:1 Depth of Scope

add axioms to increase depth

2 Breadth of Scope

add axioms to expand signature


Increasing Depth

Extend the original ontology and add semantics

Write axioms from scratch

Reuse axioms from an existing (more expressive) theory


Increasing Depth via Grafting

A less expressive ontology is grafted to a more expressive one to provideadditional, relevant semantics.

Grafting to Add Depth

An ontology T3 is the grafting of the ontology T2 onto the ontology T1 iff thereexists T ′

1,T′2,T

′3 such that

1 T ′3 is a nonconservative extension of T ′

2 such that both theories have thesame signature;

2 T ′1 faithfully interprets T ′

3;

3 Ti is language-equivalent to T ′i .


Increasing Depth via Grafting

What this looks like:

sem.owl

sem-x.owl

psl.owlpsl_dl.clif

sem.clif

sem-x.clif

psl_swrl.clif psl.swrl

sem-r.swrlsem-r.clif

Figure : Grafting SEM to psl.owl


Results: Increased Depth of Scope

Where formalization was possible:

SEM extended with grafting: answers all successfully

The Event Ontology extended with grafting: answers all successfully

LODE extended with grafting: still lacks sufficient semantics


Increasing Breadth

Extend the original theory to add concepts

Write or reuse axioms to add and define new concepts

Good news and bad news...


Increasing Breadth

The bad news:

No easy fix: Can’t simply add rules/axioms with the missing concepts

Original ontology doesn’t have the the required data

An issue of incomplete information

Fix must be implemented at the ontology level: redesign or choose a differentontology


Increasing Breadth

The good news:

Required signature expansion is feasible!

psl.owl for example


Summary

Failure to answer query

T ∪ Σ 6|= CQ

Axioms Missing Query not definable

Insufficient Semantics(Depth of Scope)

Grafting

Necessary Semanticsnot Definable

Future Work

Query LanguageRestriction

Future Work

Missing Concepts(Breadth of Scope)

Ontology Revision

Can we reuse Semantic Web Event Ontologies to support Complex EventProcessing? Yes! but...

Techniques applicable for (re)use of Semantic Web ontologies (beyond CEPspecifically)

Future work: the language barrier


Supplementary Material - Grafting I

sem x.owl:

1 TransitiveProperty( :hasSubEvent)

2 FunctionalProperty( :hastime)

3 SubClassOf( :Event ObjectSomeValuesFrom( :hastime TemporalEntity))

4 DisjointObjectClass( :Event :TemporalEntity)

5 DisjointObjectClass( :Event :Actor)

6 DisjointObjectClass( :Actor :TemporalEntity)

7 DisjointObjectClass( :Place :TemporalEntity)

8 DisjointObjectClass( :Place :Event)

9 DisjointObjectClass( :Place :Actor)

10 SubObjectProperty( ObjectPropertyChain( InverseObjectProperty(:hasSubEvent) :hasPlace) :hasPlace)

11 SubObjectProperty( ObjectPropertyChain( InverseObjectProperty(:hasSubEvent) :hasActor) :hasActor)


Supplementary Material - Grafting II

event x.owl1 TransitiveObjectProperty( :sub event)2 SubClassOf( :Event ObjectSomeValuesFrom( :time time:TemporalEntity))3 DisjointObjectClass( :Event time:TemporalEntity)4 DisjointObjectClass( :Event :Thing)5 DisjointObjectClass( :Thing time:TemporalEntity)6 DisjointObjectClass( :Thing geo:SpatialThing)7 DisjointObjectClass( :Event geo:SpatialThing)8 DisjointObjectClass( time:TemporalEntity geo:SpatialThing)9 DisjointObjectClass( time:TemporalEntity foaf:Agent)10 DisjointObjectClass( geo:SpatialThing foaf:Agent)11 DisjointObjectClass( :Event foaf:Agent)12 SubClassOf( foaf:Agent :Thing)13 SubObjectProperty(:agent :factor)14 SubObjectProperty( ObjectPropertyChain( InverseObjectProperty(

:sub event) :place) :place)15 SubObjectProperty( ObjectPropertyChain( InverseObjectProperty(

:sub event) :agent) :agent)


Supplementary Material - Grafting III

lode x.owl

1 SubClassOf( :Event ObjectSomeValuesFrom( :atTimeowltime:TemporalEntity))

2 DisjointClass( :Event owltime:TemporalEntity)

3 DisjointClass( :Event geo:SpatialThing)

4 DisjointClass( geo:SpatialThing owltime:TemporalEntity)

5 DisjointClass( dul:Object :Event)

6 DisjointClass( dul:Object owltime:TemporalEntity)

7 DisjointClass( dul:Object geo:SpatialThing)

8 DisjointClass( dul:Agent :Event)

9 DisjointClass( dul:Agent geo:SpatialThing)

10 DisjointClass( dul:Agent owltime:TemporalEntity)


Supplementary Material - CQ Results I

CQ Results (all):

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Supplementary Material - CQ Results II

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Supplementary Material - CQ Results III

CQ Formalizations

CQ1: What actors participated in the occurrence, O21? (Ans: P2)FOL: exists a (actor(a) & performed in(a,O21)).PSL.OWL: Actor and performed in value O21Event OWL: Agent and agent value O21LODE OWL: Agent and ’involved agent’ value O21SEM OWL: Actor and inverse (’has Actor’) value O21

CQ1-2: Or, what actors perform A2? (Ans: P1,P2)FOL: exists a (actor(a) & performs(a,A2)).PSL.OWL CQ1-2: Actor and performs value A2Event, LODE, SEM OWL: N/A – out of lexicon scope

CQ1-3: Or, what actors participated in some occurrences of A2? (Ans: P2)FOL: exists a exists o (actor(a) & occurrence of(o,A2) &performed in(a,o)).PSL.OWL: Actor and performed in some (occurrence of value A2)SEM: Actor and inverse (’has Actor’) some (’has event type’ valueA2)Event, LODE OWL: N/A – out of lexicon scope


Supplementary Material - CQ Results IV

CQ2: What can possibly occur next after an occurrence of A2?(Occurrences of A3,A4,or A5 as long as they are suboccs of O11 orO12)

CQ3-1: Are occurrences of A21 and A4 possibly subactivity occurrences ofthe same complex activity occurrence? (Yes – A1)

CQ3-2: Are A21 and A4 subactivities of the same complex activity?

CQ4: Are any other activities taking place at L7, at the same time as theoccurrence of A5? Ans: A3

CQ5: Assuming that occurrences of A3 and A5 are part of the samecomplex activity occurrence, what activities possibly occurredbetween them?

CQ6: What activity could have occurred before an occurrence of A5?:Ans: A2,A3,A4

CQ7 Is there an activity will definitely occur after an occurrence of A3?Ans: A5

CQ8: What activities are scheduled to occur during interval I1 at locationL4?


Supplementary Material - CQ Results V

CQ9: During what time intervals (between what timepoints) are noevents occurring at L6? Ans: all intervals exc. I7, I11

CQ10: Are there any occurrences of A3 and A5 that will overlap? (i.e.compare beginof and endof of their occs)

CQ11: What subactivities in A1 is P3 participating in? Ans: A3,A5

CQ12-1: Is P2 possibly participating in A3? Ans: yes

CQ12-2: What occurrences of A2 is P2 participating in? Ans: O21

CQ13: Given an occurrence of A2 and A3, what might P3 participate innext? Ans: O51


Supplementary Material - CQ Results VI

CQ Formalizations (full):

* FOL: binary PSL lexicon in Prover9 syntax

* OWL CQs in Manchester syntax in each event ontology lexicon; mapped

from psl_actors_locations.owl

CQ1: What actors participated in the occurrence, O21? (Ans: P2)

FOL: exists a (actor(a) & performed_in(a,O21)).

OWL CQ1: Actor and performed_in value O21

Event OWL CQ1: Agent and agent value O21

LODE OWL CQ1: Agent and ’involved agent’ value O21

SEM OWL CQ1: Actor and inverse (’has Actor’) value O21

%CQ1-2: Or, what actors perform A2? (Ans: P1,P2)

FOL: exists a (actor(a) & performs(a,A2)).

OWL CQ1-2: Actor and performs value A2

Event, LODE, SEM OWL CQ1-2: N/A -- out of lexicon scope

CQ1-3: Or, what actors participated in some occurrences of A2? (Ans: P2)


Supplementary Material - CQ Results VII

FOL: exists a exists o (actor(a) & occurrence_of(o,A2) & performed_in(a,

o)).

OWL CQ1-3: Actor and performed_in some (occurrence_of value A2)

SEM CQ1-3: Actor and inverse (’has Actor’) some (’has event type’ value

A2)

Event, LODE OWL CQ1-3: N/A -- out of lexicon scope

CQ2: What can possibly occur next after an occurrence of A2? (

Occurrences of A3,A4,or A5 as long as they are suboccs of O11 or O12

)

FOL: exists o2 exists o3 exists a3 exists o (occurrence_of(o2,A2) &

subactivity_occurrence (o2,o) & subactivity_occurrence(o3,o) &

precedes(o2,o3) & occurrence_of(o3,a3)).

OWL CQ2: N/A

Event, LODE, SEM OWL CQ2: N/A (also out of scope; missing Activity and/

or ordering of occurrences)

CQ3-1: Are occurrences of A21 and A4 possibly subactivity occurrences of

the same complex activity occurrence? (Yes -- A1)


Supplementary Material - CQ Results VIII

FOL: exists o2 exists o4 exists o exists a (occurrence_of(o2,A21) &

occurrence_of(o4,A4) & subactivity_occurrence(o2,o) &

subactivity_occurrence(o4,o) & occurrence_of(o,a)).

OWL CQ3-1: inverse(occurrence_of) some ((inverse(subactivity_occurrence)

some (occurrence_of value A21)) and (inverse(subactivity_occurrence

) some (occurrence_of value A4)))

SEM CQ3-1: inverse(’has event type’) some (’has subevent’ some (’has

event type’ value A21) and ’has subevent’ some (’has event type’

value A4))

Event, LODE OWL CQ3-1: N/A -- out of lexicon scope

CQ3-2: Are A21 and A4 subactivities of the same complex activity?

FOL: exists a subactivity(A3,a) & subactivity(A4,a).

OWL CQ3-2: inverse(subactivity) value A3 and inverse(subactivity) value

A4


CQ4: Are any other activities taking place at L7, at the same time as

the occurrence of A5? Ans: A3


Supplementary Material - CQ Results IX

FOL: exists o5 exists o exists a exists t (occurrence_of(o5,A5) &

is_occurring_at(o5,t) & occurrence_of(o,a) & -(occurrence_of(o,A5))

& occurred_at(o,L7) & is_occurring_at(o,t)).

OWL CQ4: inverse(occurrence_of) some (occurred_at value L7 and (

is_occurring_at some (inverse (is_occurring_at) some (occurrence_of

value A5))))

Event, LODE, SEM OWL CQ4: N/A -- out of lexicon scope; missing Activity

and also means of comparing timepoints/intervals

CQ5: Assuming that occurrences of A3 and A5 are part of the same complex

activity occurrence, what activities possibly occurred between them

?

FOL: exists o3 exists o5 exists ob exists ab exists o (

subactivity_occurrence(o3,o) & subactivity_occurrence(o5,o) &

occurrence_of(o3,A3) & occurrence_of(o5,A5) & subactivity_occurrence

(ob,o) & occurrence_of(ob,ab) & precedes(o3,ob) & precedes(ob,o5)).

OWL CQ5: N/A

Event, LODE, SEM OWL CQ5: out of lexicon scope (Activities, ordering);

and generally N/A in OWL


Supplementary Material - CQ Results X

CQ6: What activity could have occurred before an occurrence of A5?: Ans:

A2,A3,A4

FOL: exists ob exists o5 exists o (occurrence_of(o5,A5) &

subactivity_occurrence(o5,o) & subactivity_occurrence(ob,o) &

precedes(ob,o5)).

OWL CQ6: inverse (occurrence_of) some (subactivity_occurrence some (

inverse(subactivity_occurrence) some (occurrence_of value A5)) and

precedes some (occurrence_of value A5))

Event, LODE, SEM OWL CQ6: N/A -- out of lexicon scope (missing Activity

mapping, ordering mapping)

CQ7: Is there an activity will definitely occur after an occurrence of

A3? Ans: A5

FOL: exists an exists a (activity(an) & activity(a) &

(all o all o3 (occurrence_of(o,a) & occurrence_of(o3,A3) ->

exists on exists o (occurrence_of(on,an) &

subactivity_occurrence(on,o) & subactivity_occurrence(

o3,o) & precedes(o3,on))))).


Supplementary Material - CQ Results XI

OWL CQ7: inverse(occurrence_of) some (subactivity_occurrence some

(inverse (subactivity_occurrence) some (occurrence_of value A3)) and

inverse (precedes) some (occurrence_of value A3))


mapping and/or ordering mapping)

CQ8: What activities are scheduled to occur during interval I1 at

location L4?

FOL: exists o exists a exists t1 exists t2 exists t3 exists t4 (

occurrence_of(o,a) & begins(o,t1) & ends(o,t2) & begins(I1,t3) &

ends(I1,t4) & beforeEq(t3,t1) & beforeEq(t2,t4) & occurred_at(o,L4))

.

OWL CQ8: inverse (occurrence_of) some (begins some (inverse (beforeEq)

some (inverse (begins) value I1)) and ends some (beforeEq some (

inverse (ends) value I1))) and (occurred_at value L4)


mapping and/or relation between intervals, begin, and end)


Supplementary Material - CQ Results XII

CQ9: During what time intervals (between what timepoints) are no events

occurring at L6? Ans: all intervals exc. I7, I11

FOL: exists t1 exists t2 exists i (timepoint(t1) & timepoint(t2) &

timeinterval(i) & begins(i,t1) & ends(i,t2) &

(all o all t3 (before(t1,t3) & before(t3,t2) & is_occurring_at(o,

t3)

-> -(occurred_at(o,L6))))).

OWL CQ9: inverse (psl_interval) some (not (occurred_at value L6))

SEM CQ9: inverse (’has Time’) some (not (’has Place’) value L6)

Event OWL CQ9: inverse(event:Time) some (not (event:place value L6)

LODE OWL CQ9: inverse(’at time’) only (not (’in space’ value L6))

CQ10: Are there any occurrences of A3 and A5 that will overlap? (i.e.

compare beginof and endof of their occs)

FOL: exists o3 exists o5 exists o exists t1 exists t2 exists t3 exists

t4 (occurrence_of(o3,A3) & occurrence_of(o5,A5) &

subactivity_occurrence(o3,o) & subactivity_occurrence(o5,o) & begins

(o3,t1) & ends(o3,t2) & begins(o5,t3) & ends(o5,t4) &


Supplementary Material - CQ Results XIII

((before(t1,t3) & before(t2,t4)) | (before(t3,t1) & before(t4,t2)

))).

OWL CQ10: N/A -- something like:

occurrence_of value A3 and (begins some (before some (inverse (

begins) some (occurrence_of value A5)) and ends some (inverse

(before) some (inverse (begins) some (occurrence_of value A5)

)) and subactivity_occurrence some (inverse (

subactivity_occurrence) some (occurrence_of value A5))

BUT, we’re unable to enforce that the occurrence of A5 that is part of

the same complex occ as the occ of A3 is the same one that has the

overlapping begin/end points


mapping and/or ordering over timepoints/intervals)

CQ11: What subactivities in A1 is P3 participating in? Ans: A3,A5

FOL: exists a (subactivity(a,A1) & performs(P3,a)).

OWL CQ11: subactivity value A1 and inverse (performs) value P3


mapping and/or performs Activity mapping)


Supplementary Material - CQ Results XIV

CQ12-1: Is P2 possibly participating in A3? Ans: yes

FOL: performs(P2,A3).

OWL CQ12-1: performs value A2

Event, LODE, SEM OWL CQ12-1: N/A -- out of lexicon scope (missing

Activity mapping and/or performs Activity mapping)

CQ12-2: What occurrences of A2 is P2 participating in? Ans: O21

FOL: exists o (occurrence_of(o,A2) & performed_in(P2,o)).

OWL CQ12-2: occurrence_of value A2 and inverse (performed_in) value P2

SEM CQ12-2: ’has event type’ value A2 and ’has Actor’ value P2


CQ13: Given an occurrence of A2 and A3, what might P3 participate in

next? Ans: O51


Supplementary Material - CQ Results XV

FOL: exists o2 exists o3 exists o4 exists o exists a4 (occurrence_of(o2,

A2) & occurrence_of(o3,A3) & & subactivity_occurrence(o2,o) &

subactivity_occurrence(o3,o) & subactivity_occurrence(o4,o) &

precedes(o2,o4) & precedes(o3,o4) & performed_in(P4,o4) &

occurrence_of(o4,a4)).

OWL CQ13: inverse (performed_in) value P3 and subactivity_occurrence

some (inverse (subactivity_occurrence) some (occurrence_of value A2)

and inverse (subactivity_occurrence) some (occurrence_of value A3))

and inverse (precedes) some (occurrence_of value A2) and inverse (

precedes) some (occurrence_of value A3)


mapping and/or ordering mapping)


Science

RuleML2015: Using PSL to Extend and Evaluate Event Ontologies