RuleML2015: Using PSL to Extend and Evaluate Event Ontologies

Using PSL to Extend and Evaluate Event Ontologies
Megan Katsumi and Michael Gr¨uninger
Semantic Technologies Lab
University of Toronto
Ninth International Web Rule Symposium
August 2-5, 2015
Katsumi, Gr¨uninger (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 Event
Processing?

Event Ontologies on the Semantic Web
Some examples:
The Simple Event Model (SEM): interoperability with event information on
the web
Linked Open Descriptions of Events (LODE): aims to integrate event
information 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 with
these ontologies
Other CEP approaches can beneﬁt similarly by incorporating these ontologies
into 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 ability
of a theory
Evaluated as an entailment problem: T ∪ Σ |= CQ
If the CQ is entailed, then the semantics and signature of the theory are
suﬃcient!

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 of
the same complex activity occurrence?
CQ4 Are any other activities possibly taking place at the same place and
the same time as a particular activity?
CQ5 Assuming that occurrences of two activities are part of the same
overall activity occurrence, what activities possibly occurred
between them?
CQ6 What activity could have occurred before an occurrence of some
other observed activity?
CQ7 Is there an activity that will deﬁnitely occur after an occurrence of
some 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 applications
Generally, Semantic Web ontologies known to have reasoning limitations

Now What?
Processing?
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 3
Semantic 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 provide
additional, relevant semantics.
Grafting to Add Depth
An ontology T3 is the grafting of the ontology T2 onto the ontology T1 iﬀ there
exists T1, T2, T3 such that
1 T3 is a nonconservative extension of T2 such that both theories have the
same signature;
2 T1 faithfully interprets T3;
3 Ti is language-equivalent to Ti .

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 diﬀerent
ontology

Increasing Breadth
The good news:
Required signature expansion is feasible!
psl.owl for example

Summary
Failure to answer query
T ∪ Σ |= CQ
Axioms Missing Query not definable
Insufficient Semantics
(Depth of Scope)
Grafting
Necessary Semantics
not Definable
Future Work
Query Language
Restriction
Future Work
Missing Concepts
(Breadth of Scope)
Ontology Revision
Processing? Yes! but...
Techniques applicable for (re)use of Semantic Web ontologies (beyond CEP
specifically)
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)
:hasSubEvent) :hasActor) :hasActor)

Supplementary Material - Grafting II
event x.owl
1 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)
:sub event) :place) :place)
:sub event) :agent) :agent)

Supplementary Material - Grafting III
lode x.owl
1 SubClassOf( :Event ObjectSomeValuesFrom( :atTime
owltime: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 O21
Event OWL: Agent and agent value O21
LODE OWL: Agent and ’involved agent’ value O21
SEM 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 A2
Event, 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’ value
A2)
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 or
O12)
CQ3-1: Are occurrences of A21 and A4 possibly subactivity occurrences of
the 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 the
occurrence of A5? Ans: A3
CQ5: Assuming that occurrences of A3 and A5 are part of the same
complex activity occurrence, what activities possibly occurred
between 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 location
L4?

Supplementary Material - CQ Results V
CQ9: During what time intervals (between what timepoints) are no
events 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 in
next? 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)

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