Abstract
Introduction
A primary purpose of work on ontology is to create a common computable semantics for concepts in the world. An ontology describes the concepts and the relation between these concepts together with constraints on how to interpret them.
The role of fondational ontologies in ontology construction, matching and integration is manifold. Their potential for clarity in semantics and a rich formalization are important requirements for ontology development improving ontology quality [41,52] and preventing bad ontology design [34,75]. These ontologies may also act as semantic bridges supporting interoperability between ontologies [35,50,51].
In the semantic web and linked data in general, as stated in [3],
When a foundational ontology is used in the development and integration of domain ontologies – during or after –
Ontology matching is a research area aimed at finding ways to make different ontologies interoperable. The matching process can be seen as the task of generating a set of correspondences (i.e., an alignment) between the entities of different ontologies [18]. Correspondences express relationships between ontology entities. For instance, the concept of
Whereas the area of ontology matching has developed in the last decades, the problem of matching ontologies involving foundational ontologies has seen less development regarding automatic solutions [44,70]. This is not surprising since matching foundational and domain ontologies is a highly complex task, even when done manually. It requires the deep identification of the semantic context of concepts and, at a minimum, the identification of subsumption relations, and in a way such that the subsumption relations must of course be consistent with the formalization of the subsuming concept in the upper ontology. In fact, subsumption and other relations are often neglected by most state-of-the-art matchers.
There have been many manual efforts to make sense of how different foundational ontologies relate to other lexical and semantic data bases, and how they improve the process of matching domain ontologies. In this paper, we survey various approaches to ontology matching using foundational ontologies to create shared semantics.
An additional challenge is that there is little agreement on many of the possible goals and methods of ontology construction or the formal languages in which to encode an ontology. Developers of ontologies have variously advocated very small upper ontologies or large ones, very expressive formal logics, or very minimal ones as a way to support fast logical inference. Evaluations and surveys have typically been conducted by the authors themselves, or their collaborators and supporters (with the possible exception of [50]).
Considering this scenario, this paper reviews the following tasks of ontology matching involving foundational ontologies:
matching of foundational ontologies;
matching of foundational ontologies to lexicons;
matching domain ontologies with the help of foundational ontologies; and
matching foundational ontologies to domain ontologies.
We discuss the main strengths and weaknesses of existing approaches and highlight the challenges to be addressed in the future. We consider that this comprehensive study may set the grounds for advancing domain and foundational ontology matching.
The scope of this paper is in using foundational ontologies for matching and integration of ontologies. While this necessarily touches on the topics of how to create or evaluate ontologies themselves, we will address this topic only in the service of evaluation the use case of ontologies for matching. As such, we do not attempt to review all available foundational ontologies, but just study the use of them for matching other ontologies.
The rest of the paper is organised as follows: Section 2 introduces the different foundational ontologies and ontology matching. Section 3–Section 6 discuss the approaches in the categories (i)–(iv) introduced above. Section 7 discusses the open challenges in the field and Section 8 concludes the survey.
Background
Foundational ontologies
An ontology typically provides a vocabulary that describes a domain of interest and a specification of the meaning of terms used in the vocabulary. Depending on the precision of this specification, the notion of ontology encompasses several data and conceptual models, for example, sets of terms, classifications, database schemes, or fully axiomatized theories [80].
In particular, ontologies can be classified according to their “level of generality” [30]: We here follow the terminology proposed by [30] in distinguishing top-level and domain ontologies regarding their level of generality. More recently, the term
Several foundational ontologies have been developed, influenced by different philosophies and views on how to conceptualize reality. Several comparisons can be found in the literature, as in [43,50,76]. Some common criteria for comparing ontologies are artifact representation criteria (dimensions, representation languages, modularity) [50], ontological commitments and subject domain and applications [43].
We list a number of well-known ontologies that have documented use in ontology matching and integration efforts. We introduce the main insights behind each proposal, and current term (class+property) and axiom counts. Different variants and versions, and the availability of alignments to lexical resources (such as WordNet [54]) and ontologies are discussed in the next sections.
This list summarized in Table 1 gives an idea of the variety of foundational ontologies. One can see the variety in number of entities ranging from dozens to thousands, on the other hand there is some uniformity in adoption of the OWL standard in a majority of the listed ontologies. We point out as well that most ontologies do not publish versioned releases and exact number of classes or identifiers are not available for most. We tried to provided the most up to date counts of terms or at least order of magnitude counts for the larger ones, along with the best reference available to any online repositories where the latest versions are available.
Summary of foundational ontologies used in ontology integration, discussed in the next sections
The list is also not exhaustive as we describe only the ontologies that are more often cited in the task of ontology matching. There are other top or foundational ontologies such as SOWA’s ontology,11
Ontology matching refers to a process that consists of generating an alignment (
(Matching process).
The matching process can be seen as a function
Each of the elements featured in this definition can have specific characteristics which influence the difficulty of the alignment task.
An alignment (
(Alignment).
An alignment
A correspondence expresses a relation
(Correspondence).
A correspondence if the correspondence is if the correspondence is
The correspondence

Fragment of

Fragment of
While the RDF alignment format provided in the Alignment API16
In the following, we discuss the use of foundational ontologies in different matching tasks: (i) matching of foundational ontologies; (ii) matching of foundational ontologies to lexicons; (iii) matching domain ontologies with the help of foundational ontologies; and (iv) matching foundational ontologies to domain ontologies.
As stated in [42], while the purpose of a foundational ontology is to address interoperability among ontologies, the development of different foundational ontologies re-introduces the interoperability problem. As briefly discussed in the previous section, these ontologies have been developed directed at different classes of applications, as well as relying on different theoretical assumptions.
Early work addressed this problem [27,79,85] from different perspectives on the alignments. While [27] compared specific treatments of fundamental issues (as significant discrepancies related to universals and particulars, qualities, constitution and spatio-temporality) and how similar notions apply differently in BFO and DOLCE, [79] compared the primitive relations (dependence, quality, and constitution) between these ontologies. In [85], the alignment between BFO and DOLCE was established in order to conciliate their respective realistic and cognitive points of view and to integrate medical data. While 100% of BFO categories were aligned to DOLCE, 81% of DOLCE categories were aligned to BFO.
More recently, [90] compares BORO and UFO ontologies according to the their metaphysical choices that define their structure and composition. Instead of comparing terms in both ontologies, the authors compare how the two approaches address issues such as
Other studies addressed other foundational ontologies. In [42], alignments between BFO, DOLCE and GFO have been established with automatic matching tools and manually, with substantially fewer alignments found by the matching tools. The alignments in the context of the whole ontology revealed a considerable number of logical inconsistencies. This work has been extended in [73] in two ways: considering matching systems participating in OAEI 2018, and a new pair of aligned foundational ontologies (SUMO and DOLCE). The alignments in [42] and [59] served as a reference alignment to automatically evaluate the matchers. Examples of reference correspondences include: (
Overall, the results found are in line with what has been reported when evaluating the behaviour of matchers in the task of matching domain and foundational ontologies, which would also require identification of subsumption relations [74]. Current tools fail on correctly capturing the semantics behind the ontological concepts, which requires deeper contextualization of the concepts on the basis of their hierarchy and axioms. Addressing the identification of subsumption relations, the approach in [40] relies on extracting hypernym relations from ontology annotations for establishing such kind of correspondences. Results on exploiting lexico-syntactic patterns and definitions layout on DOLCE and SUMO were evaluated on a manually generated subsumption reference.
From another perspective, the core characterization of mereotopology (a theory of physical parts) of SUMO and DOLCE has been studied in [56], relating their axiomatizations via ontology alignments. This included corrections and additions of axioms to the analyzed theories which eliminate unintended models and characterize missing ones. Finding alignments between DOLCE and SUMO was also addressed in [59], where the SmartDOLCE and SmartSUMO ontologies have been developed on the basis of DOLCE and SUMO. The alignment of the just the taxonomic statements from SUMO to DOLCE involved extracting the upper-level of SUMO and the non-trivial task of aligning the remaining concepts to appropriate DOLCE categories.
Aligning foundational ontologies reveals also the problem of matching their different versions. In [78], a method for tracking, explaining and measuring changes between successive versions of BFO1.0, BFO1.1, and BFO2.0 was applied. The aim was to provide a more comprehensive analysis of the changes with respect to the BFOConvert tool18
Formalizeations [10] within the Common Logic Ontology Repository (COLORE), were used in the specification of alignments between upper ontologies in [28]. These alignments serve for the verification of foundational ontologies. Similarly, [11] shows how to apply techniques for ontology verification to link interpretations among ontologies.
Table 2 summarizes work on matching of foundational ontologies. They are mostly manual efforts, with a few of the resulting alignments made available.
Summary of matchings of foundational ontologies (∗
Several efforts in equipping lexical resources with foundational ontologies have been made in order to associate a formal semantics to their lexical layer. As stated in [20,21], while WordNet has been used in numerous work as an ontology, where the hyponym relations between word senses are interpreted as subsumptions relation between concepts, it is only serviceable as an ontology if some of its links are interpreted according to a formal semantics that tell us something about the world and not just about language.
For example, WordNet has the sense of “chair” as a hyponym of “seat” but only an English gloss meant for humans to read for each, and no logical semantics that defines the hyponym link, with the result that hyponyms are often incorrectly treated by users as being logically transitive. An ontology would, at a minimum, define the axiom of transitivity, and state that it holds on the hyponym relation. Most ontologies have little more than class/subclass relations however. One might also want to state that a chair is a artifact made by humans with the intent for use in supporting a seated humans. Some upper ontologies have axioms that define their terms, and some large taxonomies have terms for specific things like chairs, but very few have axiomatized large number of detailed objects, processes and relationships. This poses a problem for matching algorithms if there aren’t both detailed formalizations that can be used to objectively determine a correct match and a large inventory so that matches are not to trivially general terms like object or event.
A number of researchers have investigated different ontological problems in treating WordNet as an ontology (e.g., confusion between concepts and individuals, constraints violations, heterogeneous levels of generality, etc.) [20] and provided the WordNet taxonomy with more rigorous semantics. First the WordNet taxonomy was reorganized to meet the OntoClean [31] methodology requirements, and the resulting upper level nouns were then mapped to DOLCE classes representing their highest level categories. This alignment is concentrated on the noun database, since most particulars in DOLCE describe categories whose members are denoted by nouns. The result is the OntoWordNet resource expressing alignments between WordNet 1.6 version and DOLCE Lite Plus. An extension is presented in [24] in order to extract association relations from WordNet, and to interpret those associations in terms of a set of conceptual relations in DOLCE.
Later, this alignment has been updated [25] with a revision of the manual alignments and different versions of DOLCE and WordNet, WordNet 3.0 and (DOLCE UltraLitePlus), which is a simplified version of DOLCE Lite Plus, intended to make classes and properties names more intuitive and express axiomatizations in a simpler way, among other features.
While these works focused mostly on WordNet noun synsets, [81] extended the previous alignments by aligning verbs according to their links to nouns denoting perdurants, transferring to the verb the DOLCE class assigned to the noun that best represents that verb’s occurrence. They argue that many NLP applications need to deal with events, actions, states, and other temporal entities that are usually represented by verbs.
The alignment of WordNet to other foundational ontologies has been also addressed. In [77], a semi-automatic method for aligning WordNet 3.0 and BFO2.0 is described. It adopts previous alignments between WordNet and the KYOTO ontology, whose top layer is based on DOLCE. The method involves manually creating a set of alignments between the ontologies and implementing a set of matching rules.
In [67], the authors report the matching and integration of several background resources and ontologies of varying complexity to the Cyc knowledge base. These resources and ontologies included large pharmaceutical and medical thesauri and large portions of WordNet. For this task, ontologists have been trained with domain experts and interactive clarification dialog-based tools were developed to enable experts to directly match/integrate their ontologies. In [58], SUMO was originally mapped manually to WordNet 1.6 and then manually updated to 3.0.19
SUMO and WordNet were used in a semi-automated process to match the millions of terms in the YAGO20
Summary of matching with lexicons (∗
Finally, in [45], WordNet has been extended by applying the notion of
Table 3 summarizes the works presented in this section. There are some available alignments, approaches are mostly semi-automatic, with one case of manual alignment and one case of automatic alignment. WordNet is the lexical resource that is considered in all work listed and two different versions are involved in the alignments (1.6 and 3.0).
Foundational ontologies provide a reference for rigorous comparisons of different ontological approaches, and a framework for analysing, harmonizing, matching and integrating existing domain ontologies [59]. In domain ontology matching, in particular, they act as semantic bridges to help the task. For instance, reducing the matching space to the entities under a same category e.g., avoiding matching
Despite the potential gain of exploiting foundational ontologies in domain ontology matching, few works have addressed this alternative, possibility due to the still lack of systematic alignments between domain and foundational ontologies. This gain has been quantitatively measured in [51], where a set of algorithms exploiting such semantic bridges are applied. The circumstances of cases where foundational ontologies improve domain ontology matching, with respect to approaches ignoring them, were then studied. The experiments were conducted with SUMO-OWL (a restricted version of SUMO), OpenCyc and DOLCE and demonstrate that overall the alignment via upper ontologies impacts in F-measure positively. Additionally, in [60] a set of alignment patterns based on OntoUML (a conceptual modeling language based on UFO) are applied to a set of alignments generated by matching systems. An analysis of the impact of patterns to avoid common errors was presented.
The semi-automatic LOM matcher [48] combines WordNet synset matching (checking terms from the ontologies to be matched sharing common synsets) and
From a manually established alignment between biomedical ontologies and BFO, in [82], a matching approach relies on filtering out correspondences at domain level that relate two different kinds of ontology entities. The matching approach is based on a set of similarity measures and the use of foundational ontology as a parameter for better understanding the conceptual nature of terms within the similarity calculation step. Besides the reported improvement in the results obtained, the introduction of foundational ontologies in the alignment process increased the influence of semantic factors in this task, further expanding the universe of information to be explored during the alignment.
Summary of matching via foundational ontologias
Summary of matching via foundational ontologias
Table 4 summarizes the use of foundational ontologies as an aid to the of matching domain ontologies. Here the automatic approaches are adopted more frequently. Alignments, however, were not found to be available.
Methodologies for constructing ontologies should not neglect the use of foundational ontologies and may better address it in a
While matching foundational ontologies is mostly manually done, with more automation in matching domain ontologies via foundational ones, in this section, both approaches have been performed.
Manual alignment
Many approaches for mapping rely on a manual alignment process. In [8], DOLCE was used to integrate two geoscience knowledge representations, the GeoSciML schema and the SWEET ontology, in order to facilitate cross-domain data integration. The aim was to produce a unified ontology in which the GeoSciML and SWEET representations are aligned to DOLCE and to each other. In that perspective, DOLCE works as a semantic bridge and this approach fits in the category of domain matching with foundational ontologies. The alignments have been manually established and representation incompatibility issues have been discussed so far. Similarly, in [66], manual alignments were established between the O&M (Observations and Measurements) ontology and DOLCE, in order to restrict the interpretations of entities in the O&M model and to make explicit the relations between their categories.
DOLCE has been manually aligned to the domain ontology describing services (OWL-S) in [52], in order to address its conceptual ambiguity, poor axiomatization, loose design and narrow scope. They have also developed a core ontology of services to serve as middle level between the foundational and OWL-S, and can be reused to align other Web Service description languages.
In [13], several schemata of FactForge, which enables SPARQL queries over a LOD cloud, have been aligned to the foundational ontology PROTON in order to provide a unified way to access to the data. The alignments were created by knowledge engineers through a manual process. Equivalence e.g., (
As stated in Section 5, manual alignments have also been established between biomedical ontologies and BFO, in [82]. In this line, [9] analysed the “compatibility” between an ontology of the biomedical domain (UMLS) and the Cyc Ontology, by manually aligning UMLS to Cyc.
In [72], ontologies from the OAEI Conference track have been manually aligned to SUMO. As a complete manual alignment between SUMO and WordNet is available, such alignments have been used as bridges to facilitate the matching task. Four annotators have been worked on the alignments. Table 5 shows a fragment of the spreadsheet used for the annotators to align the domain concepts to the SUMO concepts.
Fragment of the spreadsheet for the manual alignment between cmt ontology in Fig. 2 and SUMO, via WordNet
Fragment of the spreadsheet for the manual alignment between
During the process of alignment, several difficulties arose for interpreting the real meaning that the concept represents in the domain ontology. For instance, the concepts
In contrast, one can examine a SUMO definition of a term such as
In [61], existing alignments between DBPedia ontology and DOLCE-Zero21
While the previous proposals mainly generate manual alignments, BLOOMS+ [39] is an early work on automatising the process. It has been used to automatically align PROTON to LOD datasets using as gold standard the alignments provided in [13]. BLOOMS+ first uses Wikipedia to construct a set of category hierarchy trees for each class in the source and target ontologies. It then determines which classes to align using 1) similarity between classes based on their category hierarchy trees; and 2) contextual similarity between these classes to support (or reject) an alignment. BLOOMS+ significantly outperformed existing matchers in the task.
In [69] the authors have proposed an automatic approach for matching domain and foundational ontologies that exploits existing alignments between WordNet and foundational ontologies. The matching process is divided in two main steps. The first step identifies the correct synset to a concept and the second one identifies the correspondence of a domain concept to a foundational concept. The approach has been evaluated using DOLCE and domain ontologies from the OAEI conference data set,22
IEEE Standard Ontologies for Robotics and Automation,” in IEEE Std 1872-2015, vol., no., pp.1-60, 10 April 2015.
In [49] WordNet was used as background knowledge, and their matching approach combines concept definition enrichment, disambiguation and filtering of candidate correspondences with inconsistency detection. The approach has been used for matching DOLCE+DnS Ultralite and a domain ontolology describing mobile services.
Automatic foundational distinctions of LOD entities (class vs. instance or physical vs. non-physical objects) is done in [3] with two strategies: an (unsupervised) alignment approach and a (supervised) machine learning approach. The alignment approach, in particular, relies on the linking structure of alignments between DBpedia, DOLCE, and lexical linked data, using resources such as BabelNet, YAGO and OntoWordNet. For instance, they use the paths of alignments and taxonomic relations in these resources and automated inferences to classify whether a DBpedia entity is a physical object or not.
Summary of matching with domain ontologies and cross-domain ontologies (∗
Table 6 summarizes work in alignments between domain and foundational ontologies. Several efforts have been made to align DOLCE to domain ontologies, SUMO and PROTON are also considered in more than one work. These projects use different domain ontologies, and results are unavailable is most of the cases, therefore a detailed third-party comparison of approaches is yet not possible.
The following sections discuss a series of issues regarding matching of foundational ontologies: the complexity of the task, the automation of systems with capabilities to include such alignments, the lack of evaluation data sets, the evolution of different versions and the problems that poses, the desired variety and lack of expressiveness in the alignments, and finally, multilingualism.
Complexity of the task
The problem of matching ontologies gets more complex when involving foundational ontologies, that explains why there is less development regarding automatic solutions [44,70]. It requires the deep identification of the semantic context, the identification of subsumption relations, and consistentency with the formalization. In fact, subsumption and other relations are often neglected by most state-of-the-art matchers.
As seen in the previous sections, most approaches still rely on manually or semi-automatically established alignments. This task is far from being trivial, even when done manually. This has been recently corroborated in [84], where manually classifying domain entities under foundational ontology classes is reported to be very difficult to do correctly. Manual ontology matching is also an expensive task that may introduce a bias as it represents a point of view expressing the interpretation of the concepts influenced by the background of the expert. As knowledge on foundational ontologies is specialized, it is important that such evaluation considers an overview of different experts in this area. Moreover, while manual alignment on a small set of concepts is feasible, bigger data sets would require considerable effort. The findings in [84] also point out the need for improving the methodological process of manual integration of domain and foundational ontologies, in accordance with what has been stated in [41].
Automation
While more automation is an obvious requirement in the field, the poor performance of solutions addressing automatically matching different foundational ontologies or with domain ontologies have demonstrated the difficulty of the task, as reported in experiments evaluating current matching tools [42,71]. Current tools fail on correctly capturing the semantics behind concepts (even when such semantics are present), which requires deeper contextualization on the basis of hierarchies and axioms. In that sense, further context and documentation is required, in particular for domain ontologies, to help identifying the right semantics (e.g, the ontologies from the largely used OAEI Conference dataset have a very poor lexical layer and limited or non-existent axiomatized semantics).
Furthermore, while diverse (domain) ontology matching approaches rely on external background knowledge, (BabelNet,25
Besides the points raised above, the task requires the identification of other relations than equivalences, such as subsumption and meronymy. The latter is largely neglected by current matchers. In particular, the main problem of matching foundational and domain ontologies is that, most matchers typically rely on string-based techniques as an initial estimate of the likelihood that two elements refer to the same real world phenomenon, hence the found correspondences represent equivalences with concepts that are equally or similarly written. However, in many cases, this correspondence is not the case [71]. In fact, when having different levels of abstraction it might be that the matching process is capable of identifying subsumption correspondences rather than equivalence, since the foundational ontologies have concepts at a higher level.
Evaluation
Despite the variety of tasks in the OAEI campaigns,32
Another aspect refers to the evolution or the consistency of alignments with respect to the evolution or the different variants of the ontologies. For example, DOLCE and its different variants have been used in diverse proposals, as many efforts have been dedicated to the development of this ontology. DOLCE has been exposed with reduced axiomatization and extensions with generic or domain plugins, such as for DOLCE-Lite [24], DOLCE Lite Plus33
Another issue is related to the evolution of the resources aligned to the ontologies. As stated in [61], conflicts may arise between an alignment defined on a version, and a newer version. The alignment provided for an older version may become incoherent in case of a non-conservative change of the ontology in the newer version. It is the case in the alignments between DOLCE and the different versions of DBPedia. Taking the example presented by the authors, for instance,
Evolving alignments to cope with the different versions of the ontologies is still an open challenge.
Most alignments generated in the research we have surveyed were limited to linking of a single entity of a source ontology to a single entity of a target ontology. The links lack expressiveness to a large extent. In order to better express the relationships between entities from different ontologies, they require rather full fledged axioms, as pointed out in [13,67]. In the example from [13], a complex correspondence states that the professions are modeled as instances of the class
The most significant issue in ontology matching is that most ontologies lack definitions of terms in logic, comparable to the completeness of natural language definitions in dictionaries. Most of the intended semantics of terms are left to the intuition of humans reading their names. Until richer definitions become the norm, ontology matching, whether manual or automatic, will remain difficult to conduct or evaluate.
Multilingualism
Very few foundational ontologies are equipped with lexical layers in languages other than English (e.g., BFO has been enriched with a lexical annotation in Portuguese, SUMO is the exception and is matched to the 26 languages in Open Multilingual WordNet [7]). However, with the increasing amount of multilingual data on the Web and the consequent development of ontologies in different languages, foundational ontologies should also be equipped with richer multilingual annotations in order to facilitate the multilingual and cross-lingual ontology matching tasks.
Final remarks
Ontology matching has reached some maturity in terms of matching domain ontologies. There is however room for further developments in the adoption of foundational ontologies in the task. Systematically enriching domain ontologies with foundational ones would also promote their use as semantic bridges in the task of matching domain ontologies. One of the difficulties however is the need of specialised knowledge as injecting foundational ontologies in ontology matching, in general, requires deeply understanding the foundational concepts and its relations. Another issue concerns the lack of formal definitions associated to lexicons (comments and labels) helping to understand the precise semantics of each concept. These are among the main brakes to automatising together with the points discussed above.
This paper has provided an overview of the adoption and exploration of foundational ontologies in the task of ontology matching, on different perspectives: work attempting to compare and match foundational ontologies, natural language definitions vs logical statement issues addressed by linking lexicons and foundational ontologies, the role of foundational ontologies as bridges for linking domain ontologies; and equipping existing domain ontologies with foundational distinctions. We have pointed out the limitations to be addressed in order to bring the clarity of semantics of foundational ontologies in ontologies in general.
In a broader scope, semantic web in general and its materialisation with the linked open data initiative still lack such ontological distinction, as recently stated in [3,88]. This has been further corroborated in [5], where it is stated that in the semantic web, there is an increasingly need for serious engagement with ontology, understood as a general theory of the types of entities and relations making up their respective domains of inquiry. However, there is still little interaction between the communities, despite the fact that they share common ambitions in terms of knowledge understanding. This goes beyond the matching task as discussed in this paper in the sense that is has to take into account the data being described by the ontologies.
