Addressing Issues in Foundational Ontology Mediation
Zubeida Casmod Khan and C. Maria Keet
School of Mathematics, Statistics, and Computer Science, University of KwaZulu-Natal, Durban, South Africa
UKZN/CSIR-Meraka Centre for Artificial Intelligence Research, Durban, South Africa
Keywords:
Foundational Ontology, Ontology Mediation, Semantic Interoperability, Ontology Alignment, Ontology
Mapping, Ontology Matching, Ontology Merging.
Abstract:
An approach in achieving semantic interoperability among heterogeneous systems is to offer infrastructure to
assist with linking and integration using a foundational ontology. Due to the creation of multiple foundational
ontologies, this also means linking and integrating those ones. In order to achieve this, we have selected
the widely used foundational ontologies DOLCE, BFO, and GFO, and their related modules, on which to
perform ontology mediation (alignment, mapping, and merging). The foundational ontologies were aligned
by identifying correspondences between ontology entities using seven tools, documentation, and our manual
alignments, and comparing their effectiveness. Thereafter, based on the alignments, we created correspon-
dences in the ontology files resulting in entity mappings and merged ontologies. However, during the mapping
process, it was found that differences in foundational ontologies, such as their hierarchical structure, conflict-
ing axioms due to complement and disjointness, and incompatible domain and range restriction, cause logical
inconsistencies in foundational ontology alignments, thereby greatly reducing the number of mappings. We
analyse and present these logical inconsistencies with possible solutions to some of them.
1 INTRODUCTION
There has been an exponential growth in ontology de-
velopment for the Semantic Web, including a move
toward modular and networked ontologies. Founda-
tional ontologies are commonly used to facilitate se-
mantic interoperability. However, Semantic Web sys-
tem developers use their ontologies with a preferred
foundational ontology. The semantics and underlying
Ontology of each foundational ontology differs, caus-
ing a problem in semantic interoperability. Heteroge-
neous systems on the Semantic Web are restricted to
committing to a single foundational ontology in order
to promote interoperability. However, no single foun-
dational ontology is used across all systems, therewith
preventing interoperability. In order for these applica-
tions to share and process information correctly, there
is a need for foundational ontology interoperability,
so that ontology developers committing to a preferred
foundational ontology will achieve seamless linking
to other domain ontologies linked to another foun-
dational ontology. Such an infrastructure was envi-
sioned as the “WonderWeb Foundational Ontologies
Library” (WFOL) (Masolo et al., 2003), but this in-
frastructure still does not exist. The main precondi-
tions for a WFOL are content comparisons and ontol-
ogy mediation. Ontology mediation refers to identi-
fying and solving differences between heterogeneous
ontologies, in order to allow reuse and interoperabil-
ity. Its three main processes are alignment, mapping,
and merging (de Bruijn et al., 2006). There are only
few paper-based alignments of foundational ontolo-
gies, being between GFO and DOLCE (Herre, 2010)
and between DOLCE and BFO (Seyed, 2009; Temal
et al., 2010), which, however, are partial, with older
versions of the ontologies, informal, and/or aligned
but not mapped. To the best of our knowledge, no
systematic comparison of the contents of foundational
ontologies has been done, nor full alignments, let
alone providing consistent mappings.
We aim to contribute to fill this gap of semantic in-
teroperability by selecting three well-known founda-
tional ontologies, DOLCE (Masolo et al., 2003), BFO
(http://www.ifomis.org/bfo) with RO (Smith et al.,
2005), and GFO (Herre, 2010) with which we per-
form a rigorous foundational ontology content com-
parison and mediation to aid in achieving founda-
tional ontology interchangeability. The alignment
process is carried out by using the manual alignment
as a gold standard and (semi-)automated alignment
with seven alignment tools to examine them on their
capabilities to align foundational ontologies. The ac-
5
Keet C. and Dawood Z..
Addressing Issues in Foundational Ontology Mediation.
DOI: 10.5220/0004518000050016
In Proceedings of the International Conference on Knowledge Engineering and Ontology Development (KEOD-2013), pages 5-16
ISBN: 978-989-8565-81-5
Copyright
c
2013 SCITEPRESS (Science and Technology Publications, Lda.)
curacy and percentage of alignments that were found
vary greatly among the tools due to their diverse
alignment algorithms, ranging from 18 to 94% and 17
to 31%, respectively. Further alignment issues appear
in the transitivity of alignments across the three foun-
dational ontologies due to absence of some entity or
conflicting parthood theories, whilst some may be re-
solved by asserting them as sibling classes. Mapping
the aligned entities whilst keeping a consistent ontol-
ogy reduces the feasible set from 85 alignments to 43
successful mappings due to disjointness and comple-
ment axioms elsewhere in the ontology, and due to in-
compatible domain and range axioms, which in some
cases can be solved from a logic viewpoint by assert-
ing subsumption instead. For each mediation process
(alignment, mapping and mediation), we present the
issues encountered for foundational ontology media-
tion and aim to solve these issues.
In the remainder of the paper, we provide a liter-
ature review in Section 2. A high-level content com-
parison of the foundational ontologies is described in
Section 3, which is followed by an analysis of align-
ments in Section 4, and of the mappings in Section 5.
We discuss the results in Section 6 and conclude in
Section 7.
2 LITERATURE REVIEW
There has not been much work done in comparing
content of the foundational ontologies. By this, we
mean comparing their classes, properties and rela-
tions. Some work on comparing the primitive rela-
tions of BFO (i.e., the Relation Ontology (RO)) and
DOLCE has been done (Seyed, 2009) where it is
found that the philosophies behind the foundational
ontologies affect the way the relations are modelled.
For instance, BFO is based on realist principles and
has no abstract entities while GFO is both descriptive
and realist in nature and allows abstract entities in an
ontology, and BFO’s parthood relation has part does
not consider abstract entities, while GFO has a part-
hood relation abstract has part that considers abstract
entities at a higher-level than its has part relation.
Temal et al. (Temal et al., 2010) created a BFO-
DOLCE mapping in order to integrate medical in-
formation. The classes (universals or categories) are
mapped with equivalence and subsumption relations.
Based on the older so-called SNAP and SPAN version
of BFO, they found that all BFO universals were suc-
cessfully mapped to DOLCE, but not all DOLCE enti-
ties could be mapped to BFO. These alignments were
not checked on consistency of the mappings and were
done on some First Order Logic version of the on-
tologies, where the SNAP-BFO has, e.g., Boundary,
that BFO v1.1 in OWL does not have, and DOLCE
is claimed to have Collection, which appears neither
in the principal documentation (Masolo et al., 2003)
nor in the OWLized version of DOLCE. Some of their
alignments are useful, however, which we will return
to in Section 4.
From a computational viewpoint instead of an On-
tology and modelling viewpoint, we consider several
aspects of ontology mediation and matching. Ontol-
ogy mediation (de Bruijn et al., 2006) is divided into
three operations: mapping, alignment, and merging.
To be precise in the terminology we use throughout
the paper, we provide several definitions on ontology
matching in this section, which are taken from (Eu-
zenat and Shvaiko, 2007), Chapter 3. First, there is
the actual mediation, or matching, process:
Definition 1 (Matching Process). The matching pro-
cess can be seen as a function f which, from a pair of
ontologies to match o and o
0
, an input alignment A, a
set of parameters p and a set of oracles and resources
r, returns an alignment A
0
between these ontologies:
A
0
= f (o, o
0
, A, p, r).
To be able to talk about an actual alignment or
mapping, the notion of “entity language” has to be
introduced, which is used to express precisely those
entities that will be matched.
Definition 2 (Entity language). Given an ontology
language L, an entity language Q
L
is a function from
any ontology o L which defines the matchable enti-
ties of ontology o.
Then, a correspondence consists of a relation be-
tween two entities in different ontologies, which is
uniquely identified and has some confidence value as-
signed to it.
Definition 3 (Correspondence). Given two ontolo-
gies o and o
0
with associated entity languages Q
L
and Q
L
0
, a set of alignment relations θ and a confi-
dence structure over Ξ, a correspondence is a 5-tuple:
hid, e, e
0
, r, ni, such that id is a unique identifier of the
given correspondence, e Q
L
(o) and e
0
Q
0
L
0
(o
0
),
r θ, and n Ξ.
Ontology alignment, then, is the process of spec-
ifying correspondences between entities, by using a
particular alignment relation, such as equivalence,
subsumption, or a predefined similarity relation.
Definition 4 (Alignment). Given two ontologies o
and o
0
, an alignment is made up of a set of correspon-
dences between pairs of entities belonging to Q
L
(o)
and Q
L
0
(o
0
) respectively.
Ontology mapping deals with creating correspon-
dences between ontologies based on alignments such
KEOD2013-InternationalConferenceonKnowledgeEngineeringandOntologyDevelopment
6
that the resultant ontology is still consistent and does
not have unsatisfiable classes or relations. Euzenat
and Shvaiko do consider this with respect to models
of aligned ontologies, which is too lengthy to repeat
here, and De Bruijn et al. does not provide a definition
of their idea of mapping as a ‘consistent alignment in
the context of the whole ontology’ either. Therefore,
we capture the gist in the following definition, using
Euzenat and Shvaiko’s notational conventions.
Definition 5 (Mapping). Given two ontologies o and
o
0
, a mapping is made up of a set of correspon-
dences between pairs of entities belonging to Q
L
(o)
and Q
L
0
(o
0
), respectively, and this mapping is satis-
fiable and does not lead to an unsatisfiable entity in
either o or o
0
.
In merging, a new merged ontology is created
from the original ontologies.
Definition 6 (Merging). Given two ontologies o and
o
0
, a merging is the creation of a new ontology o
00
containing o and o
0
and all mappings between entities
belonging to Q
L
(o) and Q
L
0
(o
0
) such that o
00
does not
have unsatisfiable entities and is consistent.
Overviews of approaches, frameworks, and tech-
nologies used to perform ontology mapping, align-
ment and merging are discussed elsewhere (e.g.,
(de Bruijn et al., 2006)), and more detail about al-
gorithms and issues can be found in (Euzenat and
Shvaiko, 2007).
A number of tasks for the problem at hand are
based on ontology mediation. Performing founda-
tional ontology mediation with automated tools is a
good approach and a starting point because there are
many foundational ontology modules, and founda-
tional ontologies are constantly being updated. It is
rather time-consuming to explore each foundational
ontology, especially when there are differences in
hierarchy and structure. By applying several tools
to align foundational ontologies, one can determine
which tools are better suited for foundational ontolo-
gies, and the type of alignments that are misaligned
or not discovered by tools. We summarize the align-
ment tools that are used in the experimental evalua-
tion, of which we note that LogMap, YAM++, Hot-
Match, Hertuda and Optima have been evaluated with
positive results by the Ontology Alignment Evalua-
tion Initiative (OAEI) in terms of their precision, re-
call and other performance measures.
H-Match (Castano et al., 2003) is an algorithm
for matching ontologies at different depth levels, with
different accuracies, based on user choices. The algo-
rithm takes into account linguistic and semantic fea-
tures of ontologies to perform matching and uses one
of four matching models: surface, shallow, deep or in-
tensive. The surface model only considers linguistic
affinity between entity names to measure similarity.
In shallow, deep and intensive models, context is also
considered to determine entity similarity.
PROMPT (Noy and Musen, 2000) is an ontology
matching plug-in for Prot
´
eg
´
e that allows for compar-
ison, mappings, and merging between ontologies. It
is a semi-automatic method that invokes algorithms
based on a combination of concept-representation
structure, the relations between entities and user’s ac-
tions. PROMPT offers the user four different algo-
rithms to use for initial comparison: lexical match-
ing, FOAM plugin, lexical matching with synonyms
and using UMLS concept identifiers for matching. It
is only supported in older versions of Prot
´
eg
´
e, which
makes it unstable.
LogMap (Jim
´
enez-Ruiz and Cuenca Grau, 2011)
automatically generates mappings between ontolo-
gies using logic-based semantics of the input ontolo-
gies. It offers an improvement to other mapping tools
in that it addresses scalability and logical inconsisten-
cies. LogMap allows a user to upload ontologies in a
number of formats and implements existing reasoners
to check the satisfiability of the ontologies.
YAM++ (Ngo and Bellahsene, 2012) aligns en-
tities by information retrieval or machine learning if
training data is available. Three matchers are imple-
mented in YAM++: an element level matcher, a struc-
tural matcher and a semantic matcher. The element
level and structural mapper discover alignments while
the semantic matcher revises these alignments to re-
move inconsistencies and ensure logical mappings.
HotMatch (Dang et al., 2012) is a tool based on a
combination of many matching algorithms. The two
types of algorithms are element level and structural
matching. However, there is more than one of each
implemented. There are also filters in HotMatch, used
to remove duplicate mappings found by the matchers.
Upon input of a source and target ontology, HotMatch
deploys its matchers and filters sequentially resulting
in mappings between the two.
Hertuda (Hertling, 2012) is an entity matcher that
applies element level matching with a string compar-
ison. The alignments generated by Hertuda are only
satisfiable in OWL Lite/DL. As a result, object prop-
erties in the ontologies are handled separately. This
may cause some difficulties in aligning object prop-
erties in the foundational ontologies because their do-
mains and ranges affect the alignments.
Optima (Kolli and Doshi, 2008) is a fully auto-
matic tool which iteratively improves alignments. It
is aimed at aligning large ontologies but may also be
used for smaller ontologies. Its similarity measure is
based on both syntactic and semantic similarity.
AddressingIssuesinFoundationalOntologyMediation
7
3 FOUNDATIONAL ONTOLOGY
CONTENT COMPARISON
In this section, we provide an informal content com-
parison between the foundational ontology pairs by
identifying differences and similarities between the
them. A content comparison is beneficial in that it
forms the basis for performing ontology mediation
operations. A content comparison does not include
abstract comparisons such as those based on philo-
sophical choices, ontological alignments and software
engineering properties, which has been addressed
elsewhere (Khan and Keet, 2012), but rather a high-
level comparison of the structure, organisation, and
entities of the foundational ontologies.
DOLCE, BFO and GFO contain both 3D and 4D
entities. Both BFO and GFO name these entities Con-
tinuant and Occurrent while DOLCE names them en-
durant and perdurant. Some syntactic variants ex-
ist between DOLCE, BFO, and GFO, e.g., DOLCE’s
space-region vs. BFO’s SpatialRegion vs. GFO’s
Spatial region. In DOLCE, BFO, and GFO, classes
that share the same name and idea are process, func-
tion and role.
DOLCE entities are of type particular, BFO’s en-
tities are Universals while GFO contains a combina-
tion of the two, both Individual and Universal entities.
DOLCE and BFO have similar structures at a high-
level only in that both have separate branches of 3D
and 4D entities. GFO’s high-level structure is differ-
ent as it offers a distinction between Category and In-
dividual entities. DOLCE’s endurant and perdurant
branches are linked by participation relations; BFO’s
and GFO’s 3D and 4D entity branches are completely
independent of each other.
DOLCE and GFO have advanced support for rep-
resenting entity properties (e.g., colour) and their val-
ues (e.g., blue) while BFO has limited support for
this. To describe these entities, DOLCE uses the
terms quality, quale and quality-space, BFO uses the
term Quality while GFO names these entities Prop-
erty, Property value and Value space. DOLCE’s
quality branch is disjoint to its endurant and perdu-
rant branches. In BFO, on the other hand, Qual-
ity is subsumed by Continuant branch, while GFO
has Property subsumed by the higher-level Individ-
ual. BFO’s temporal entities, including temporal re-
gions, intervals, and instants, are subsumed by Oc-
current, while DOLCE’s temporal entities are split up
into three parts, being temporal regions that are sub-
sumed by abstract entities, temporal qualities that are
subsumed by quality entities, and subclasses of perdu-
rants. All of GFO’s temporal entities are subsumed
by its Space-time entity, which is disjoint to its Con-
crete and Abstract entities. Most of DOLCE’s spatial
entities are subsumed by its abstract entity with the
exception of spatial-location-q which is subsumed by
quality, while GFO’s spatial entities are subsumed by
its space-time entity. BFO’s SpatialRegion entity is
subsumed by Continuant. DOLCE and GFO have ab-
stract entities while BFO does not.
DOLCE and GFO contain relational properties.
BFO does not have relational properties included in
the ontology, but rather as a separate ontology, the
Relational Ontology (RO) (Smith et al., 2005). BFO
2.0 is currently being developed, where BFO is in-
tegrated with RO. DOLCE’s relational properties are
all based on either of its six primitive relations: part-
hood, temporary parthood, constitution, participation,
quality, and quale. For mereology, DOLCE adopts the
axioms of General Extensional Mereology (GEM).
BFO core is a comprehensive mereology represented
in first-order logic and contains collections, sums and
universal axioms. GFO’s mereology contains the fol-
lowing axioms: antisymmetry, transitivity, set inclu-
sion, proper parthood, and other GFO-specific axioms
based on these.
Thus, the organisation of entities within the three
ontologies differ. In some cases, entities that seem
similar fall in contradicting or disjoint classes. These
differences in structure and organisation may cause
inconsistencies when performing mapping, as we
shall see later in detail.
4 ALIGNMENT
For foundational ontology alignment, i.e., aligning on
an entity-by-entity basis, certain aspects of the un-
derlying philosophies of each foundational ontology
have been ignored, because else it would result in few
or no alignments and for practical usage of their OWL
files, they are less pressing issues (e.g., DOLCE is
descriptive and contains particulars, while BFO is re-
alist and contains universals). We align classes and
object properties with equivalence relations first, and
use subsumption relations afterward to resolve some
mapping inconsistencies.
We create alignments for 20 pairs of ontologies.
These ontologies include DOLCE-Lite, BFO, GFO,
FunctionalParticipation, SpatialRelations, and Tem-
poralRelations (which are more-detailed modules of
DOLCE), BFORO and GFO-Basic. BFORO refers
to the merged ontology of BFO with the RO, and
GFO-Basic is a less-detailed module of GFO. We per-
form ontology alignment by using existing tools, doc-
umentation and manually using the content compari-
son, entity axioms and annotations. Further, for each
KEOD2013-InternationalConferenceonKnowledgeEngineeringandOntologyDevelopment
8
resource (tool, documentation or manual alignment),
we measure its accuracy by firstly examining each of
its output alignments to determine whether or not the
equivalence relation is correct. Thereafter we define
accuracy as the number of ‘correct’ alignments over
the total alignments given by the resource (Eq. 1),
where ‘correct’ denotes the alignment is also in the
set of alignments found manually, i.e., what is typi-
cally considered as the ‘gold standard’. We define the
found measure of the resources as the number of cor-
rect alignments over the total possible correct align-
ments, after manual intervention (Eq. 2).
Accuracy =
|correct alignments|
|total alignments
resource
|
× 100 (1)
Found =
|correct alignments|
|total alignments
gold
|
× 100 (2)
4.1 Alignment Results
We describe the results of the manual alignments first,
and then the results obtained with the matching tools.
4.1.1 Manual Alignments
The yield of the manual alignments between the
main foundational ontologies (DOLCE-Lite, BFO
and GFO) resulted in 17 alignments for DOLCE-Lite
BFO, 23 alignments for BFO GFO and 35
alignments for GFO DOLCE-Lite, hence, 75 in to-
tal; the complete set of alignments can be accessed
at http://www.thezfiles.co.za/ROMULUS/. Of these
75 alignments, 37 are for alignments between object
properties and are displayed in Tables 1, 2, and 3. The
mapped class alignments are available and discussed
elsewhere (Khan and Keet, 2013) and online accessi-
ble, and the difference between class alignments and
mappings for GFO DOLCE-Lite are displayed in
Table 4. When we consider entity alignments includ-
ing the related modules of the foundational ontologies
(e.g., GFO-Basic), there is a total of 85 alignments.
Naturally, there are many more than 85 alignments
if we consider identical alignments that occur among
the same entities in related modules; e.g., DOLCE-
Lite:particular GFO:Individual and FunctionalPar-
ticipation:particular GFO:Individual. There are 14
alignments common between these three ontologies,
which is displayed in Table 5.
The manual alignments were aided by the GFO
documentation (Herre, 2010) and checked against the
alignments proposed by (Temal et al., 2010; Seyed,
2009). The GFO documentation (Herre, 2010) con-
tains a list of similarities between GFO and DOLCE
which helped with the alignment process. Some of
Table 1: Equivalence alignments for relational properties
between DOLCE-Lite and BFO; the alignments numbered
in bold font can also be mapped.
DOLCE-Lite BFORO
1. generic-location located in
2. generic-location-of location of
3. part has part
4. part-of part of
5. proper-part has proper part
6. proper-part-of proper part of
7. participant has participant
8. participant-in participates in
Table 2: Equivalence alignments for relational properties
between DOLCE-Lite and GFO; the alignments numbered
in bold font can also be mapped.
DOLCE-Lite GFO
1. generic-constituent has constituent part
2. generic-constituent-of constituent part of
3. generically-dependant-on depends on
4. generic-dependant necessary for
5. has-quale has value
6. quale-of value of
7. boundary has boundary
8. boundary-of boundary of
9. q-present-at exists at
10. temporary-participant-in agent in
11. temporary-participant has agent
12. generic-location occupies
13. generic-location-of occupied by
14. part abstract has part
15. part-of abstract part of
16. proper-part has proper part
17. proper-part-of proper part of
18. participant has participant
19. participant-in participates in
Table 3: Equivalence alignments for relational properties in
BFO and GFO; the alignments in bold are also mapped.
BFORO GFO
1. has part has part
2. part of part of
3. has proper-part has proper part
4. proper part of proper part of
5. has participant has participant
6. participant in participates
7. located in occupies
8. location of occupied by
9. has agent has agent
10. agent in agent in
the alignments could not be used, however, due to
changes in the two foundational ontologies. We were
able to use 42% of the alignments from the docu-
mentation. We discuss four equivalence alignments
from (Temal et al., 2010). We changed the align-
ment bfo:ProcessualEntities dolce:perdurant to
bfo:Occurrent dolce:perdurant, because by defini-
AddressingIssuesinFoundationalOntologyMediation
9
tion occurrents and perdurants both represent entities
that have temporal parts and unfold in time. Temal
et al.s alignment of bfo:Quality with dolce:physical-
quality is more precise than ours, because, as men-
tioned above, we chose to ignore the some philoso-
phies (the realist debate) with the hope of achieving
a higher number of alignments. That is, our mapping
has bfo:Quality dolce:quality, thereby ignoring the
fact that BFO does not consider abstract entities. We
agree with bfo:SpatialRegion dolce:space-region
and bfo:TemporalRegion dolce:temporal-region,
and use this equivalence, too. Seyed (Seyed, 2009)
examined only three relations—dependency, quality,
and constitution—and found that they are different in
DOLCE and BFO. The basic numbers of the align-
ments are included in Table 6.
Table 4: Equivalence alignments for classes between
DOLCE-Lite and GFO ontologies; the alignments num-
bered in bold font can also be mapped.
DOLCE-Lite GFO
1. particular Individual
2. endurant Presential
3. physical-endurant Discrete presential
4. physical-object Material object
5. amount-of-matter Amount of substrate
6. perdurant Occurrent
7. process Process
8. state State
9. abstract Abstract
10. set Set
11. quality Property
12. quale Property value
13. quality-space Value space
14. time-interval Chronoid
15. space-region Spatial Region
16. temporal-region Temporal Region
4.1.2 Automated Alignments
Table 7 lists the numbers of alignments found by the
selected tools. We describe some further data in the
remainder of this section.
H-Match generated many alignments, but most of
the output was not accurate. Many entity pairs that
were matched using H-Match were found to be incor-
rectly aligned; e.g., DOLCE-Lite:quale bfo:Role.
This resulted in us being able to use only 18% of
these alignments, with the rest being false positives.
PROMPT was generally unstable resulting in force
closure of the application. It generated suggestions
of which we were able to use 56%, with the rest being
false positives; e.g., bfo:Site gfo:Situoid.
While LogMap provided few alignments between
the foundational ontologies (less than ten in all
cases), most alignments were accurate. The one
Table 5: Common alignments between DOLCE-Lite, BFO
and GFO.
DOLCE-Lite BFORO GFO
Class
1. endurant Independent
Continuant
Presential
2. physical-object Object Material object
3. perdurant Occurrent Occurrent
4. process Process Process
5. quality Quality Property
6. space-region SpatialRegion Spatial region
7. temporal-region Temporal-
Region
Temporal region
Relational property
1. proper-part has proper part has proper part
2. proper-part-of proper part of proper part of
3. participant has participant has participant
4. participant-in participates in participates in
5. generic-location located in occupies
6. generic-
location-of
location of occupied by
Table 6: Comparison of manually performed alignment ac-
curacies of the GFO documentation (Herre, 2010), related
works, and ours, and aggregates for mappings.
Seyed Herre Temal
et al.
Ours
Class alignments
DOLCE-Lite
BFO
- - 2/7 9/9
BFO GFO - - - 13/13
GFO
DOLCE-Lite
- 13/31 - 16/16
Object property alignments
DOLCE-Lite
BFO
0 - - 8/8
BFO GFO - - - 10/10
GFO
DOLCE-Lite
- 0 - 19/19
Overall alignments
Total 0/0 13/31 2/7 75/75
Accuracy 0% 42% 29% 100%
Found 0% 37% 12% 100%
Overall mappings
Total 0/0 8/31 1/7 40/40
Accuracy 0% 26% 14% 100%
Found 0% 61% 9% 100%
false positive in LogMap was the alignment of
bfo:IndependentContinuant gfo:Independent.
YAM++ generated many alignments. However, while
most of the alignments for DOLCE BFO and BFO
GFO were accurate, only about half were accurate
for GFO DOLCE. Overall we were able to use
almost 64% of its alignments. Like LogMap, YAM++
also incorrectly aligned bfo:IndependentContinuant
gfo:Independent. Some of YAM++’s other false
positive alignments include dolce:generic-constituent
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Table 7: Comparison of alignment accuracies of the matching tools and aggregates for mappings.
H-Match PROMPT LogMap YAM++ Hot Match Hertuda Optima
Class alignments
DOLCE-LiteBFO 4/16 3/8 2/2 4/4 3/3 3/3 4/12
BFOGFO 5/31 7/12 7/8 6/7 7/7 7/7 8/14
GFODOLCE-Lite 4/25 4/8 3/3 8/11 5/5 5/5 5/16
Object property alignments
DOLCE-LiteBFO 0 0 0 0 0 0 0/1
BFOGFO 0 0 4/4 0 0 0 1/3
GFODOLCE-Lite 0 4/4 0 5/14 5/7 6/8 2/23
Overall alignments
Total 13/72 18/32 16/17 23/36 20/22 21/23 20/69
Accuracy 18% 56% 94% 64% 91% 91% 29%
Found 17% 24% 21% 31% 27% 28% 27%
Overall mappings
Total 10/72 11/32 16/17 15/36 11/22 12/23 13/69
Accuracy 14% 34% 94% 42% 50% 52% 19%
Found 25% 28% 40% 38% 28% 30% 33%
gfo:has sequence constituent, dolce:quality-
space gfo:Space and dolce:temporary-proper-part
gfo:has constituent part.
HotMatch generated a fair amount of alignments
between the ontologies. Overall, we were able to
use 91% of HotMatch’s alignments, with just 2 align-
ments out of all 22 being false positives. Hertuda’s
output was surprisingly similar to HotMatch’s output,
with just one more alignment than HotMatch. We
were able to use 91% of Hertuda’s alignments, with
just 2 alignments out of all 23 being false positives.
Common false positives in YAM++, Hertuda and Hot-
Match were the alignments between dolce:part
gfo:has part and dolce:part-of gfo:part of, which
is discussed in Section 4.2.1. Optima generated many
alignments for each pair. However, there were many
false positives, consequently we were able to use 29%
of its alignments overall. This may be because Op-
tima is aimed at aligning large ontologies and the
foundational ontologies in question are of reasonable
size. Optima incorrectly aligned gfo:Continuous
bfo:Continuant, dolce:Region bfo:SpatialRegion
and dolce:dependent-place bfo:Dependent.
4.2 Alignment Issues
We have encountered two types of issues in align-
ment: transitivity, where there was no ‘full circle’
alignment between some entities of the three ontolo-
gies, and approximate alignments, where there is no
clear relationship to describe the match.
4.2.1 Transitivity
Transitivity in entity alignments works as follows: if
the equivalence relation holds between entities from
the first and second ontology and it holds between
entities from the second and third ontology; it nec-
essarily holds between entities from the first and
third ontology. Applying transitivity to entity align-
ments assists in detecting errors. For instance, if
one were to align dolce:endurant gfo:Persistant,
and gfo:Persistant bfo:Continuant, then by tran-
sitivity this means that dolce:endurant is equivalent
to bfo:Continuant, which is incorrect. In most cases,
the foundational ontology alignments are transitive.
There were two types of exceptions, being the ab-
sence of an entity and what can be termed conse-
quences of conflicting philosophies.
Absence of an Entity. An alignment cannot be a
candidate for transitivity if there is an equivalence be-
tween only two out of the three ontologies. From the
three main ontology alignments, the following ones
were not transitive due to the absence of an entity:
Absence of a DOLCE entity (7 cases): bfo:Entity
gfo:Entity, bfo:DependentContinuant
gfo:Dependent, bfo:ObjectBoundarygfo:Mate-
rial boundary, bfo:Function gfo:Function,
bfo:Role gfo:Role, bfo:has agent
gfo:has agent, bfo:agent in gfo:agent in.
Absence of a GFO entity (1 case): dolce:spatio-
temporal-region bfo:SpatioTemporalRegion
Absence of a BFO entity (17 cases): gfo:Individual
dolce:particular, gfo:Amount of substrate
dolce:amount-of-matter, gfo:State
dolce:state, gfo:Abstract dolce:abstract,
gfo:Set dolce:set, gfo:Property value
dolce:quale, gfo:Value space dolce:quality-
space, gfo:Chronoid dolce:time interval,
gfo:has constituant part dolce:generic-
consitituant, gfo:constituant part of
dolce:generic-constituant-of, gfo:necessary for
dolce:generic-dependent, gfo:depends on
AddressingIssuesinFoundationalOntologyMediation
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dolce:generically-dependent-on, gfo:has value
dolce:has-quale, gfo:value of dolce:quale-
of, gfo:has boundary dolce:boundary,
gfo:boundary of dolce:boundary-of,
gfo:exists at dolce:q-present-at
From this type of transitivity issue, we see that for the
three main ontology alignments, in most cases BFO
entities are absent. There are a few cases of absent
DOLCE entities and one case of an absent GFO entity.
Conflicting Philosophies. The philosophies of
foundational ontologies affect their entities to a cer-
tain extent. In some cases, two entities that are
aligned to each other may not be aligned to the same
entity of a third ontology.
dolce:physical-endurant bfo:Material-
Entity, dolce:physical-endurant gfo:Discrete
presential and bfo:MaterialEntity gfo:Material
persistant. Let us align bfo:MaterialEntity
dolce:physical-endurant, ignore their underlying
philosophies (i.e., that BFO is an ontology of
universals and DOLCE of particulars). However,
in GFO, there are two entities for representing
this type of entity, based on distinct philosophical
notions: gfo:Discrete presential, being subsumed
gfo:Individual, is suited for dolce:physical-
endurant while gfo:Material persistant, being
subsumed by gfo:Universal, is suited for
bfo:MaterialEntity.
dolce:part bfo:has part, dolce:part
gfo:has abstract part and bfo:has part
gfo:has part (idem for their inverses). In
DOLCE, both the domain and range of part is
particular. In BFORO, there is no domain and
range for has part. In GFO, both the domain and
range of abstract has part is Item, while both the
domain and range for has part is Concrete. The
former relational property may be better suited
for DOLCE because it is a descriptive ontology
and contains abstract entities. The latter is better
suited for BFORO as it is a realist ontology,
representing the world as is, thereby containing
concrete entities only.
The ontology matching tools discussed in Sec-
tion 4.1.2 misaligned dolce:part gfo:has part and
their inverses. This is because object property incon-
sistencies are not fully recognised by reasoners (Keet,
2012), hence their conflicting domains and ranges did
not affect the satisfiability of the ontology.
4.2.2 Approximate Alignments
There are a number of approximate alignments be-
tween foundational ontology entities. By this we
mean that they are not equivalent to each other or sub-
sumed by one another, but share some common char-
acteristics. By identifying these relations between
these entities, foundational ontology developers could
possibly relate them as sibling classes by grouping
them both under a common superclass. We mention
three of them.
dolce:arbitrary-sum, bfo:ObjectAggregate and
gfo:Configuration: All three of these entities de-
scribe a collection of something. dolce:arbitrary-
sum, however, has no unity criterion e.g., a pencil
and laundry basket are together a dolce:arbitrary-
sum, and it can contain both dolce:physical-
endurant and dolce:non-physical-endurant enti-
ties. dolce: physical-endurant is not restricted
just to instances of dolce:physical-object but can
possibly include dolce:feature and dolce:amount-
of-matter. bfo:ObjectAggregate, on the other
hand, has overall unity and can be considered
as a whole. It is restricted to bfo:Object only,
and in the case of BFO, all objects are physi-
cal. gfo:Configuration is simply a collection of
gfo:Presential facts. gfo:Presentials are not re-
stricted to whole physical objects and can include
other gfo:Presential entities. For this reason, it
cannot equate to bfo:ObjectAggregate. Further-
more, it holds a restriction that it must contain
at least one material entity. dolce:arbitrary-sum
could contain physical, non-physical or both enti-
ties, with no restrictions.
dolce:state and bfo:SpatioTemporalInstant:
DOLCE describes dolce:state by using an exam-
ple of a rock erosion describing state as a time in-
terval of the erosion is collapsed into a time point.
Similarly BFO defines bfo:SpatioTemporalInstant
as a “connected spatiotemporal region at a
specific moment”. The difference between the
two lies in the fact that dolce:state is homeomeric
while bfo:SpatioTemporalInstant is not.
dolce:relevant-part and bfo:FiatObjectPart:
DOLCE describes dolce:relevant-part as a feature
that is a relevant part of their host; e.g., the edge
of a cube. BFO defines bfo:FiatObjectPart as a
material entity that is part of an object but not
demarcated by physical discontinuities; e.g.,
the lower portion of the leg. In this sense they
are both part objects that are physical entities.
However, it is unclear whether dolce:relevant-part
is demarcated by physical discontinuities or not
and whether BFO’s fiat object parts are ‘relevant’
somehow. This requires further investigation.
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5 MAPPING AND MERGING
Ontology Mapping uses the alignments from the
alignment process to create correspondences between
entities in the ontologies. The output from the align-
ment process is broader, while the output from the
mapping process is narrower as inconsistencies affect
the mapping process. Merging is performed by creat-
ing a new ontology of the source ontologies with their
mappings between each other. Ontology mapping and
merging was performed by relating classes and object
properties in Prot
´
eg
´
e. Entities were mapped in the
order of their level in the hierarchy, from higher to
lower level, because foundational ontologies by defi-
nition are general high-level ontologies. Therefore, in
mapping, preference must be first given to high-level
entities to have agreement among general entities and
avoid inconsistencies at that level.
Alignments that cannot be mapped due to logical
inconsistencies result in unsuccessful mappings. The
inconsistencies were identified by using the following
method. For each candidate class mapping:
1. Assert the equivalence for the found alignment.
2. Run the automated reasoner.
3. Check if there are any unsatisfiable classes.
4. If there are unsatisfiable classes, use the reasoner
explanation feature to generate an explanation.
5. Analyse explanations.
6. Remove inconsistent mapping, if applicable.
For each candidate object property mapping, since
object property inconsistencies and flaws are not
properly recognised by reasoners (Keet, 2012), we
identified inconsistencies by checking if an object
property pair’s domain and range restrictions are sat-
isfiable by using the above method.
The numbers in bold face in Table 5 represent the
alignments that resulted in successful mappings be-
tween the common entities of the three main ontolo-
gies. From the 14 alignments in Table 5, six success-
ful mappings exist. Recall from the previous section
on alignment, there was a total of 85 distinct align-
ments between all foundational ontologies and related
modules, and 75 alignments between the main foun-
dational ontologies. Performing the method to iden-
tify inconsistencies in alignments resulted in 42 dis-
tinct logical inconsistencies of which 35 alone were
from the main ontologies. From all the distinct equiv-
alence alignments, only half were satisfiable and re-
sulted in successful mappings. Comparing these map-
pings to the alignments found by the tools, LogMap
doubled its percentage found to 40% and performed
best compared to the six others evaluated (see Table 7,
bottom three rows).
To solve inconsistencies in the mapping attempts,
we analysed each alignment on the logical explana-
tion for the inconsistency and the description of the
entity provided by the foundational ontology develop-
ers, and checked whether it was possible to change the
alignment from equivalence to subsumption. How-
ever, there are still many unsolvable inconsistencies,
mainly due to hierarchical and structural differences
in the foundational ontologies. Due to space limita-
tions, we describe only a representative selection of
the logical inconsistencies and (logically satisfiable)
possible solutions; the full list of inconsistencies is
available at http://www.thezfiles.co.za/ROMULUS/.
Inconsistencies Due to Disjoint Classes. For this
type of inconsistency, the entities to be aligned are
disjoint to each other, either directly, through higher-
level equivalence relations or through their subclasses
or superclasses. If entities are disjoint, they cannot
overlap, hence cannot be equivalent.
dolce:temporal-region - gfo:Temporal region -
bfo:TemporalRegion: The issue with incompat-
ible temporal regions between BFO, GFO, and
DOLCE is depicted in Fig. 1 and is a result of
the OWL DisjointClasses class axiom between
gfo:Concrete, gfo:Space Time and gfo:Abstract,
and between dolce:Abstract and dolce:Per-
durant, or, from the other viewpoint: because
BFO made TemporalRegion an Occurrent,
DOLCE made it Abstract, and GFO neither. This
does not seem to be resolvable.
bfo:Role - gfo:Role: gfo:Processual role is a sub-
class of gfo:Role and gfo:Process. gfo:Process
is a subclass of gfo:Occurrent. gfo:Occurrent is
equivalent to bfo:Occurrent. bfo:Role is a sub-
class of bfo:Continuant. bfo:Continuant is dis-
joint to bfo:Occurrent. In this equivalence re-
lation, both gfo:Role and gfo:Occurrent are su-
perclasses of gfo:Processual role, and bfo:Role
is a subclass of bfo:Continuant; gfo:Occurrent
and bfo:Continuant are disjoint, hence the two
classes cannot be equivalent. Solution: Logi-
cally, bfo:Role cannot be equivalent to gfo:Role.
However, bfo:Role can be subsumed by gfo:Role.
Therefore the relation can be changed to gfo:Role
subsumes bfo:Role.
gfo:necessary for - dolce:generic-dependent: If
we were to equate these object properties, we
would have to assume that their domains and
ranges are equivalent, which is not the case;
the situation is depicted in Fig. 2. Solution:
Logically, gfo:necessary for cannot be equiva-
lent to dolce:generic-dependent, because equat-
ing their domains and ranges causes inconsis-
tencies. However, dolce:generic-dependents
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bfo:TemporalRegion
bfo:Occurent
gfo:Occurrent
gfo:Concrete gfo:Space_Time
gfo:Temporal_Region
×
declaring equivalence results in inconsistency due to
disjointness among higher-level categories
×
gfo:Abstract dolce:Abstract
dolce:temporal-region
×
dolce:Perdurant
bfo:TemporalRegion
bfo:Occurent
Figure 1: Graphical depiction of why the aligned gfo:Temporal Region, bfo:TemporalRegion, and dolce:temporal-region cannot
be mapped in any way without causing an inconsistency; : aligned entities, ×: disjoint entities.
gfo:Item
gfo:Category gfo:Individual
×
declaring equivalence results in
inconsistency due to disjointness
and mappings among higher-
level categories
dolce:Particular
gfo:necessary_for
dolce:generic-dependent
Figure 2: Visualisation of the root cause of the
non-mappable gfo:necessary for and DOLCE-Lite:generic-
dependent; ×: disjointness, : equivalence mapping.
domain and range, dolce:particular can logi-
cally be subsumed by gfo:necessary fors do-
main and range, gfo:Item. Therefore the relation
can be changed to gfo:necessary for subsumes
bfo:generic-dependent.
dolce:generic-location - bfo:located in: This
issue is due to disjointness among domain/range.
dolce:generic-locations range is dolce:particular
and bfo:located ins range is bfo:Continuant.
bfo:Continuant is disjoint to bfo:Occurrent
and bfo:Occurrent dolce:perdurant. In
DOLCE, perdurant v has-Quality.temporal-
location-q and the domain of dolce:has-
Quality is dolce:particular (the superclass of
dolce:perdurant). Thus, bfo:Continuant is dis-
joint to has-Quality.temporal-location-q, and
cannot be equivalent, causing the range re-
strictions to be unsatisfiable in the alignment.
Therefore dolce:generic-location cannot map to
bfo:located in.
Other unresolvable cases are, among others, dolce:set
- gfo:Set and dolce:quality-space - gfo:Value space.
Inconsistencies Due to Complement Classes. For
this type of inconsistency, the entities to be aligned
were found to be complements of each other, either
directly, through higher-level equivalences or through
subsumption. We describe here one such case.
bfo:MaterialEntity - gfo:Material
persistant,
which is visualised in Fig. 3. The cru-
cial aspect in GFO is the class axiom
Universal v instantiated by.Item, and the com-
plement for individuals. Concerning mappings,
bfo:IndependentContinuant gfo:Presential.
gfo:Material_persistant
gfo:Universal gfo:Item
declaring equivalence results in
inconsistency due to the complement
bfo:IC
instantiated_by some
gfo:Individual
NOT instantiated_by some
gfo:Presential
bfo:MaterialEntity
Figure 3: Visualisation of the root cause of the non-
mappable bfo:MaterialEntity and gfo:Material persistant; :
equivalence mapping, IC = IndependentContinuant.
However, GFO has Presential v Individual
and Individual v ¬∃instantiated by.Item.
Thus, gfo:Material persistant is a subclass
of gfo:instantiated by some gfo:Item while
bfo:MaterialEntity is a subclass of the com-
plement of that class, hence bfo:MaterialEntity
cannot be equivalent to gfo:Material persistant.
Solution: The alignment can be changed into
bfo:MaterialEntity - gfo:Discrete presential,
which avoids the complement issue but it is
not free of argument (recall the “conflicting
philosophies” item in Section 4.2.1).
6 DISCUSSION
Given the size of the ontologies and our high toler-
ance by ignoring underlying philosophies, the amount
of alignments, and, even more so, the amount of map-
pings is less than one may have expected; or: once
investigated in detail, the foundational ontologies are,
at present, not particularly interchangeable even at the
logical level. Only six pairwise mappings exist, i.e.,
they being, essentially, equivalent throughout all three
examined foundational ontologies.
Concerning feasibility to carry out automated
alignments, in most cases, the tools evaluated with
the OAEI performed better than the others, with the
exception of Optima. LogMap had the highest ac-
curacy, because it also considers the logic-based se-
mantics of the ontologies and uses automated reason-
ing services throughout the process, therewith elim-
inating those false positives that would have led to
a logical inconsistency. However, LogMap gener-
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ated very few alignments compared to other accu-
rate tools (YAM++, Hertuda and HotMatch), indicat-
ing that the additional heuristics implemented are too
strict at least for foundational ontology alignment.
Most false positive alignments generated by
the tools, such as bfo:IndependentContinuant
gfo:Independent, indicate that the algorithms imple-
ment syntactic matching, which, based on the results
we obtained, is not sufficient or suitable for foun-
dational ontology matching because many entities
have a common syntax e.g., dolce:quality-space
gfo:Space both have the string ‘space’ in common but
are entirely different entities; Table 8 includes a selec-
tion of such false positives that are caused by syntactic
matching in the tools when aligning the three founda-
tional ontologies. The tools failed to recognise simple
alignments such as dolce:perdurant gfo:Occurrent,
bfo:Quality gfo:Property. In this sense, semantic
matching is not considered, or if it is, it fails to recog-
nise synonyms of the philosophical scope on which
foundational ontologies are built upon. Structural
matching is not an effective method either, due to the
fact that the hierarchies and structures of the founda-
tional ontologies differ greatly which causes the root
distances of mappable entities to differ. For aligning
foundational ontologies, it will be useful if existing
semantic matchers would include something alike a
‘philosophy WordNet’ that specialises in philosophi-
cal terms, synonyms, and definitions used in founda-
tional ontologies.
Table 8: False positives caused by syntactic matching gen-
erated by the alignment tools; the terms in italics represent
the strings that are common between aligned entities.
DOLCE-Lite BFO
physical-region ConnectedSpatio
TemporalRegion
non-physical-object Object
region SpatioTemporalRegion
BFO GFO
IndependentContinuant Independent
Site Situoid
Continuant Continuous
GFO DOLCE-Lite
has sequence
constituent
generic-constituent
has-part part
Space quality-space
The results of the tool analysis is a good indica-
tion of which tools to experiment with for founda-
tional ontology alignment in general. However, they
found less than a third of the actual alignments at this
stage, and therefore it is still vital to perform manual
alignment for foundational ontologies. The tools also
did not generate subsumption relations for any of the
alignments, but this could perhaps be an extension to
the basic idea of LogMap by means of another call
to the reasoner. One could investigate whether Op-
tima is useful to identify accurate alignments among
the larger foundational ontologies SUMO (Niles and
Pease, 2001) and YAMATO (Mizoguchi, 2010).
On a positive note, the systematised list of issues
now can be taken up by ontologists. While some of
the inconsistencies found are quite elaborate, others
should be easier to resolve both ontologically (philo-
sophically) and where in the ontology the entity is
positioned; e.g., the notion of a mathematical Set is
fairly well investigated already, and likewise the dif-
ferent theories of parthood. As such, the results pre-
sented here provide a solid foundation for ample on-
tological investigations. From an engineering view-
point and in case of urgent need for interoperability,
one could take a quite different strategy: OWL 2 EL
does not have negation, and therefore it should be pos-
sible to assert more mappings between the OWL 2 EL
modules of the foundational ontologies. Whether that
is the best strategy is a different matter, and it does not
take away the substantial list for which there was no
transitivity due to ‘missing’ entities. In any case, we
now know that some mappings are possible, hence,
also some foundational ontology interoperability.
7 CONCLUSIONS
The foundational ontologies DOLCE, BFO, and GFO
were pairwise aligned and mapped. They were
aligned manually, which served as the ‘gold stan-
dard’, and with the aid of seven alignment tools. The
accuracy and percentage of alignment found were
compared, where LogMap had the highest accuracy
with 94% and HotMatch and Hertuda as close sec-
ond, and YAM++ found the most correct alignments
(31% of the total manual alignments among the three
main ontologies (75)). The evaluation of the tools in-
dicated that the algorithms currently implemented by
the tools are not well-suited for foundational ontology
mediation. Semantic matching in the tools need to be
improved to include philosophical synonyms which
are used in foundational ontologies. Declaring the
correspondences in all ontology files based on its 85
alignments resulted in only 43 mappings, with the re-
maining 42 causing logical inconsistencies. The in-
consistencies are due primarily to differences in their
respective hierarchical structure with conflicting ax-
ioms, such as complement and disjointness, and in-
compatible domain and range restriction. On closer
inspection, some inconsistencies may be resolved us-
ing subsumption or making them sibling classes.
AddressingIssuesinFoundationalOntologyMediation
15
Future research includes mapping other founda-
tional ontologies, adding subsumption mappings, and
evaluating the current alignments with the founda-
tional ontology developers. We also aim to imple-
ment a facility for community input on the alignments
and mappings, which could to be facilitated via the
foundational ontology library that is available online
at http://www.thezfiles.co.za/ROMULUS/.
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