Evolution in
OWL 2 QL & OWL 2 EL Ontologies
Dmitriy Zheleznyakov
28th of January, 2014, Oslo
Ontology
General
rules:
Schema:
o To use ontologies in applications,
we need special, formal syntax
Cleric
is-a
Pope

All popes are clerics
Facts:
Data:
Pope(Benedict XVI)
Benedict XVI is a pope
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Ontology
Schema:
Cleric
is-a
Pope
Data:
o Do ontologies differ from data bases?
o Data bases: explicit knowledge only
o Benedict XVI is a pope
o Ontologies: explicit & implicit knowledge
o Benedict XVI is a pope
o Reasoning: Benedict XVI is a cleric
Data:
Pope(Benedict XVI)
reasoning
Cleric(Benedict XVI)
Explicit knowledge
Implicit knowledge
2
Ontology Languages
Schema:
Cleric
is-a
Pope
o The focus of this work:
ontology languages for the Semantic Web
o Web Ontology Language: OWL 2 (W3C
Standard)
o OWL 2 QL
o OWL 2 EL
Data:
o Good computational properties
o Efficient schema and data management
o Used in practice
Pope(Benedict XVI)
3
OWL 2 QL: Ontology-Based Data Access
o Ontology-Based Data Access (OBDA)
o provide unified query interface
to heterogeneous data sources
…
4
OWL 2 QL: Ontology-Based Data Access
o Ontology-Based Data Access (OBDA)
o provide unified query interface
to heterogeneous data sources
o EU FP7 project Optique will develop
an OBDA system
o use-case partners: Statoil, Siemens
o Ontologies may change:
o new knowledge about domain
o new data source is added
o Motivation for our work:
o to address the dynamicity of OBDA systems
by studying evolution of schema and data
…
4
OWL 2 EL: Clinical Science, Bio Ontologies
o Ontologies enable communication and
knowledge sharing
between doctors, scientists, etc.
il dottore
o SNOMED CT: > 311k terms
o constantly under development:
o 5 modification teams
o every 2 weeks
the main team integrates changes,
o 2002  2008
SNOMED went 278k  311k terms
o It is the standard to describe the results of
experiments in the US clinical labs
o Motivation for our work:
o to provide techniques that facilitate
ontology development for such a vast
community
el doctor
5
Our Goal
o To facilitate evolution of ontology-based systems
o insertion of knowledge
o deletion of knowledge
o On two levels:
o schema
Original ontology
Schema:
o data
Cleric
is-a
o With as little changes
as possible
Pope
Data:
Pope(Benedict XVI)
To insert
Cleric
is-a
Priest
To delete
Pope(Benedict XVI)
6
How to Approach the Problem?
Original ontology
Schema:
Schema:
Cleric
is-a
Pope
Pope(Benedict XVI)
• a conceptual understanding
of how to evolve ontologies
• checking its computational
properties
Cleric
is-a
Data:
1. Define an operator and
understand it
New knowledge
Priest
Data:
2. Develop an algorithm to
compute the result
3. Implement the algorithm
Priest(Adam)
Resulting ontology
Schema:
Cleric
is-a
Pope
is-a
Priest
Data:
Priest(Adam)
Pope(Benedict XVI)
7
Previous Work
Model-based operators
Formula-based operators
Many evolution operators
proposed
[AGM’85]
[Borgida’85]
[Dalal’88]
[Winslett’88]
[Satoh’88]
[Katsuno&Mendelzon’91]
[Winslett’90]
AI: 80’s – 90’s
Propositional logic,
weaker then
OWL 2 QL & OWL 2 EL
Adaptation
of some operators
[Kang&Lau’04]
[Liu& al’06]
[Flouris&al’04]
[Qi&Du’09]
[Flouris&al’05]
[DeGiacomo&al’07-09]
[Qi&al’06] [Wang&al’10]
KR: 2004-2006 2007-2010
8
General Overview of the Results
Work for restriction
For
of OWL 2 QL
OWL 2 QL & EL
- inexpressibility
OWL 2 QL
- counterintuitive
results OWL 2 EL
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
- inexpressibility
- counterintuitive
results
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
9
Understanding Model-Based Operators
Work for restriction
of OWL 2 QL
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
10
Understanding Model-Based Operators
o We have shown: operators are determined
by three parameters
o this gives a three-dimensional space
of operators
o Classical operators fit in this space
o Novel operators can be easily defined
by changing parameters
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Understanding Model-Based Operators
o We noticed: operators are determined
by three parameters
o this gives a three-dimensional space
of operators
o Classical operators fit in this space
o Novel operators can be easily defined
by changing parameters
o We can add new values to dimensions!
o more operators can be defined!
11
Inexpressibility of Model-Based Operators
Work for restriction
of OWL 2 QL
inexpressibility
- counterintuitive
results
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
12
Inexpressibility of Model-Based Operators
Schema:
Wife
hasHusband
Husband
Disjoint with
Schema:
Wives are married to their husbands
Priest cannot be husbands
Priest
Data:
hasHusband(Mary,John)
Priest(Adam)
Priest(Bob)
Facts:
Mary is married to John and
Adam and Bob are priests
13
Inexpressibility of Model-Based Operators
a model:
Schema:
Wife
hasHusband
Husband
Disjoint with
Priest
Priest
Adam
hasHusband
Mary
John
Bob
Data:
hasHusband(Mary,John)
Priest(Adam)
Priest(Bob)
Data to add:
Under model-based operators:
We incorporate new knowledge
directly into models
Facts to add:
John is a priest
Priest(John)
13
Inexpressibility of Model-Based Operators
Priest
Adam
hasHusband
Mary
1.
Priest
hasHusband
Adam
John
Bob
Bob
John
John cannot be a husband of
Mary anymore!
What happens to her?
2.
Three options:
1. She divorced
2. She married some one else
3. She married to a former priest
Priest
Adam
hasHusband
Mary
Jack
Bob
John
Data to add:
3.
Priest
Adam
Priest(John)
hasHusband
Mary
Bob
John
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Inexpressibility of Model-Based Operators
Priest
Adam
hasHusband
Mary
1.
Priest
hasHusband
Adam
John
Bob
Bob
John
We showed:
all these options cannot be captured
in OWL 2 QL and OWL 2 EL
OR
2.
Adam
We need at least disjunction which is
not in OWL 2 QL and OWL 2 EL
Data to add:
Priest
Mary
Jack
Bob
John
OR
3.
Priest
Adam
Priest(John)
hasHusband
hasHusband
Mary
Bob
John
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Bad Behaviour of Model-Based Operators
Work for restriction
of OWL 2 QL
inexpressibility
- counterintuitive
results
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
14
Bad Behaviour of Model-Based Operators
Some of model-based operators behave as follows:
Schema:
Data:
No schema
Facts:
Adam and Bob are priests
Priest(Adam)
Priest(Bob)
Data to add:
Facts to add:
John is a priest
Priest(John)
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Bad Behaviour of Model-Based Operators
Some of model-based operators behave as follows:
Schema:
Priest
Adam
Bob
Such behaviour
is not useful
Data:
for any application
Priest(Adam)
Priest(Bob)
Data to add:
Expected
result:
Priest
Adam
Actual
result:
Priest
John
Bob
John
Priest(John)
15
Restriction of OWL 2 QL
Work for restriction
of OWL 2 QL
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
16
Restriction of OWL 2 QL
o We found the reason of the bad
behaviour of model-base operators:
Schema:
Wife
hasHusband
Husband
Disjoint with
A binary relation participates
in disjointness
Priest
o Priest cannot be husbands
o What if we forbid
this bad interaction?
o We showed:
most of model-based operators work!
o this fragment captures (FO part of) RDFS
(another W3C standard)
Priest
Adam
hasHusband
Mary
John
Bob
disjoint with
17
Summing up on Model-Based Operators
o Model-based operators
o suffer from inexpressibility
o tend to lose too much of information
o counterintuitive behaviour
o Our verdict:
o model-based operators are not suitable
for the case of OWL 2 QL or OWL 2 EL
o We turned to Formula-based operators!
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Formula-Based Operators
Work for restriction
of OWL 2 QL
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
- inexpressibility
- counterintuitive
results
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
19
Formula-Based Operators
Schema:
Male
Male
o Preserve all the knowledge:
both explicit and implicit
is-a
Cleric
o Example: delete Priests are Males
is-a
is-a
o We do not want to lose info that
Adam is Male
Priest
Explicit
schema
Data:
Implicit
schema
Data:
Priest(Adam)
Male(Adam)
Explicit
data
Implicit
data
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Formula-Based Operators
Schema:
Male
Male
o Preserve all the knowledge:
both explicit and implicit
is-a
Cleric
is-a
is-a
o How to delete it in such a way
that it will not appear even implicitly?
Priest
Explicit
schema
o Example: delete Priests are Males
Implicit
schema
o Delete
o either Priests are Clerics
o or Clerics are Males
Schema to delete:
Male
is-a
Priest
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Formula-Based Operators
o Preserve all the knowledge:
both explicit and implicit
o Example: delete Priests are Males
The resulted schema:
either
or
Male
o How to delete it in such a way
that it will not appear even implicitly?
Male
Male
Cleric
Cleric
is-a
Cleric
is-a
Priest
Priest
o Delete
o either Priests are Clerics
o or Clerics are Males
Priest
o What to do with a multiple choice?
Classical approaches:
o Keeping both – impossible
o Combining them
o too much of information is lost
o we proved: it is computationally hard
20
Bold Operator
Work for restriction
of OWL 2 QL
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
21
Bold Operator
There is no way to decide
which resultdelete
is better!Priests are Males
o Example:
This is application dependent and
o How to delete it in such a way
should be up to the user
that it will not appear even implicitly?
o Delete
o either Priests are Clerics
The resulted schema:
o or Clerics are Males
either
or
Male
Male
is-a
Cleric
Cleric
is-a
Priest
Priest
o What to do with a multiple choice?
o We propose: Bold operator.
It picks up one of them
o The result is non-deterministic…
o … But can be computed
in polynomial time (for OWL 2 QL)
o In the case of OWL 2 EL:
o Implicit knowledge can be infinite
o Bold operator does not work
22
Tunable Operator
Work for restriction
of OWL 2 QL
Model-based
operators
Bold
operator
Works for
OWL 2 QL
Tunable
operator
Works for
OWL 2 QL & EL
Formula-based
operators
Propositional
logic
OWL 2 QL
OWL 2 EL
23
Tunable Operator
Schema:
o Tunable operator
Male
Male
is-a
disjoint with
Cleric
is-a
Husband
Priest
Explicit
schema
is-a
Husband
o allows to choose
what part of implicit knowledge
will be preserved
disjoint with
Implicit
schema
24
Tunable Operator
Schema:
o Tunable operator
Male
Male
is-a
disjoint with
Cleric
is-a
is-a
Husband
o allows to choose
what part of implicit knowledge
will be preserved
Priest
Explicit
schema
Implicit
schema
24
Tunable Operator
No implicit part
Whole implicit part
25
Summing up on Formula-Based Operators
o Classical Formula-based operators
o suffer from inexpressibility
o tend to lose too much of information
o Bold operator:
o works for OWL 2 QL
o fails for OWL 2 EL
o Tunable operator:
o works for both OWL 2 QL and OWL 2 EL
26
Current Work
o Applying our results to the Optique project
o in progress
o Incorporating evolution in transition systems
o IJCAI’2013
o Information hiding & Controlled query evaluation
o ISWC 2013
o submitted to an international conference
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