Upper ontology (information science)

In information science, an upper ontology (top-level ontology, or foundation ontology) is an attempt to create an ontology which describes very general concepts that are the same across all domains. The aim is very broad semantic interoperability between a large number of ontologies accessible "under" this upper ontology. As the metaphor suggests, it is usually a hierarchy of entities and associated rules (both theorems and regulations) that attempts to describe those general entities that do not belong to a specific problem domain.

The seemingly conflicting use of metaphors implying a solid rigorous bottom-up "foundation" or a top-down imposition of somewhat arbitrary and possibly political decisions is no accident - the field is characterized by controversy, politics, competing approaches and academic rivalry.

Development

Upper ontologies are also commercially valuable, creating competition to define them. Peter Murray-Rust has claimed that this leads to "semantic and ontological warfare due to competing standards", and accordingly any standard foundation ontology is likely to be contested among commercial or political parties, each with their own idea of 'what exists'.

No one upper ontology has yet gained widespread acceptance as a de facto standard. Different organizations are attempting to define standards for specific domains. The 'Process Specification Language' (PSL) created by the National Institute for Standards and Technology (NIST) is one example.

There is debate over whether the concept of using a single, shared upper ontology is even feasible or practical at all. There is further debate over whether the debates are valid - often leading to outright censorship and boosterism of particular approaches in supposedly neutral sources "including this one. Some of these arguments are outlined below, with no attempt to be comprehensive. Please do not censor them because you promote some ontology."

Why an upper ontology is not feasible

Historically, many attempts in many societies have been made to impose or define a single set of concepts as more primal, basic, foundational, authoritative, true or rational than others. In the kind of modern societies that have computers at all, the existence of academic and political freedoms imply that many ontologies will simultaneously exist and compete for adherents. While the differences between them may be narrow and appear petty to those not deeply involved in the process, so too did many of the theological debates of medieval Europe, but they still led to schisms or wars, or were used as excuses for same. The tyranny of small differences that standard ontologies seek to end may continue simply because other forms of tyranny are even less desirable. So private efforts to create competitive ontologies that achieve adherents by virtue of better communication may proceed, but tend not to result in long standing monopolies.

A deeper objection derives from ontological constraints that philosophers have found historically inescapable. Some argue that a transcendental perspective or omniscience is implied by even searching for any general purpose ontology - "see God's eye view"- since it is a social / cultural artifact, there is no purely objective perspective from which to observe the whole terrain of concepts and derive any one standard.

A narrower and much more widely held objection is implicature: the more general the concept and the more useful in semantic interoperability, the less likely it is to be reducible to symbolic concepts or logic and the more likely it is to be simply accepted by the complex beings and cultures relying on it. In the same sense that a fish doesn't perceive water, we don't see how complex and involved is the process of understanding basic concepts.

*There is no self-evident way of dividing the world up into concepts, and certainly no non-controversial one
* There is no neutral ground that can serve as a means of translating between specialized (or "lower" or "application-specific") ontologies
* Human language itself is already an arbitrary approximation of just one among many possible conceptual maps. To draw any "necessary correlation" between English words and any number of intellectual concepts we might like to represent in our ontologies is just asking for trouble. (WordNet, for instance, is successful and useful precisely because it does not pretend to be a general-purpose upper ontology; rather, it is a tool for semantic / syntactic / linguistic disambiguation, which is richly embedded in the particulars and peculiarities of the English language.)
* Any hierarchical or topological representation of concepts must begin from some ontological, epistemological, linguistic, cultural, and ultimately pragmatic perspective. Such pragmatism does not allow for the exclusion of politics between persons or groups, indeed it requires they be considered as perhaps more basic primitives than any that are represented.

Those who doubt the feasibility of general purpose ontologies are more inclined to ask “what specific purpose do we have in mind for this conceptual map of entities and what practical difference will this ontology make?” This pragmatic philosophical position surrenders all hope of devising the encoded ontology version of “everything that is the case,” Wittgenstein, Tractatus Logico-Philosophicus).

According to Barry Smith in "The Blackwell Guide to the Philosophy of Computing and Information" (2004), "the project of building one single ontology, even one single top-level ontology, which would be at the same time non-trivial and also readily adopted by a broad population of different information systems communities, has largely been abandoned." (p. 159)

Finally there are objections similar to those against artificial intelligence; Technically, the complex concept acquisition and the social / linguistic interactions of human beings suggests any axiomatic foundation of "most basic" concepts must be cognitive, biological or otherwise difficult to characterize since we don't have axioms for such systems. Ethically, any general-purpose ontology could quickly become an actual tyranny by recruiting adherents into a political program designed to propagate it and its funding means, and possibly defend it by violence. Historically, inconsistent and irrational belief systems have proven capable of commanding obedience to the detriment of harm of persons both inside and outside a society that accepts them. How much more harmful would a consistent rational one be, were it to contain even one or two basic assumptions incompatible with human life?

Why an upper ontology is feasible

Most of the objections to upper ontology refer to the problems of life-critical decisions or non-axiomatized and difficult to understand problem areas such as law or medicine or politics. Some of these objections do not apply to infrastructure or standard abstractions that are defined into existence by human beings and closely controlled by them for mutual good, such as electrical power system connections or the signals used in traffic lights. No single general metaphysics is required to agree that some such standards are desirable. For instance, while time and space can be represented many ways, some of these are already used in interoperable artifacts like maps or schedules.

Most proponents of an upper ontology argue that several good ones may be created with perhaps different emphasis. Very few are actually arguing to discover just one within natural language or even an academic field. Most are simply standardizing some existing communication.

Several common arguments against upper ontology can be examined more clearly by separating issues of concept definition (ontology), language (lexicons), and facts (knowledge). For instance, people have different terms and phrases for the same concept. However, that does not necessarily mean that those people are referring to different concepts. They may simply be using different language or idiom. Formal ontologies typically use linguistic labels to refer to concepts, but the terms mean no more and no less than what their axioms say they mean. Labels are similar to variable names in software, evocative rather than definitive.

A second argument is that people believe different things, and therefore can't have the same ontology. However, people can assign different truth values to a particular assertion while accepting the validity of certain underlying claims, facts, or way of expressing an argument with which they disagree. "Using, for instance, the issue/position/argument form."

Even arguments about the existence of a thing require a certain sharing of a concept, even though its existence in the real world may be disputed. Separating belief from naming and definition also helps to clarify this issue, and show how concepts can be held in common, even in the face of differing belief. For instance, wiki as a medium may permit such confusion but disciplined users can apply dispute resolution methods to sort out their conflicts, e.g. Wikipedia ArbCom.

Advocates argue that most disagreement about the viability of an upper ontology can be traced to the conflation of ontology, language and knowledge, or too-specialized areas of knowledge: many people, or agents or groups will have areas of their respective internal ontologies that do not overlap. If they can cooperate and share a conceptual map at all, this may be so very useful that it outweighs any disadvantages that accrue from sharing. To the degree it becomes harder to share concepts the deeper one probes, the more valuable such sharing tends to get. If the problem is as basic as opponents of upper ontologies claim, then, it applies also to a group of humans trying to cooperate, who might need machine assistance to communicate easily.

If nothing else, such ontologies are implied by machine translation, used when people cannot practically communicate. Whether "upper" or not, these seem likely to proliferate.

Available ontologies

Cyc

A well-known and quite comprehensive ontology available today is Cyc, a proprietary system under development since 1985, consisting of a foundation ontology and several domain-specific ontologies (called "microtheories"). A subset of that ontology has been released for free under the name OpenCyc, and a more or less unabridged version is made available for non-commercial use under the name ResearchCyc.

Basic Formal Ontology (BFO)

The [http://www.ifomis.org/bfo BFO] or Basic Formal Ontology framework developed by [http://ontologist.com Barry Smith] and his associates consists in a series of sub-ontologies at different levels of granularity. The ontologies are divided into two varieties: SNAP (or snapshot) ontologies, comprehending continuant entities such as three-dimensional enduring objects, and SPAN ontologies, comprehending processes conceived as extended through (or as spanning) time. BFO thus incorporates both three-dimensionalist and four-dimensionalist perspectives on reality within a single framework. Interrelations are defined between the two types of ontologies in a way which gives BFO the facility to deal with both static/spatial and dynamic/temporal features of reality. Each SNAP ontology is an inventory of all entities existing at a time. Each SPAN ontology is an inventory (processory) of all the processes unfolding through a given interval of time. Both types of ontology serve as basis for a series of sub-ontologies, each of which can be conceived as a window on a certain portion of reality at a given level of granularity. An example of an application of BFO can be seen in the Ontology for Biomedical Investigations (OBI).

DOLCE and DnS

Developed by Nicola Guarino and his associates at the Laboratory for Applied Ontology ( [http://www.loa-cnr.it/ LOA] ), the Descriptive Ontology for Linguistic and Cognitive Engineering ( [http://wonderweb.semanticweb.org/deliverables/documents/D18.pdf DOLCE] ) is the first module of the WonderWeb foundational ontologies library. As implied by its acronym, DOLCE has a clear "cognitive bias", in that it aims at capturing the ontological categories underlying natural language and human commonsense. DOLCE, however, does not commit to a strictly referentialist metaphysics related to the intrinsic nature of the world. Rather, the categories it introduces are thought of as cognitive artifacts, which are ultimately depending on human perception, cultural imprints and social conventions. In this sense, they intend to be just "descriptive" (vs "prescriptive") notions, that assist in making already formed conceptualizations explicit. DOLCE is an ontology of particulars, in the sense that its domain of discourse is restricted to them. Of course, universals are used to organize and characterize the particulars, but they are not themselves subject to being organized and characterized (e.g., by means of metaproperties).

[http://www.loa-cnr.it/Papers/D07_v21a.pdf DnS] (Descriptions and Situations), developed by Aldo Gangemi (LOA, Rome), is a "constructivist" ontology that pushes DOLCE’s descriptive stance even further. DnS does not put restrictions on the type of entities and relations that one may want to postulate, either as a domain specification, or as an upper ontology, and it allows for context-sensitive ‘"redescriptions"’ of the types and relations postulated by other given ontologies (or ‘ground’ vocabularies). The current OWL encoding of DnS assumes DOLCE as a ground top-level vocabulary. DnS and related modules also exploit ‘Codeps’ (Content Ontology Design Patterns), a newly created tool which provides a framework to annotate ‘focused’ fragments of a reference ontology (i.e., the parts of an ontology containing the types and relations that underly ‘expert reasoning’ in given fields or communities).

Both DOLCE and DnS are particularly devoted to the treatment of social entities, such as e.g. organizations, collectives, plans, norms, and information objects. The [http://www.loa-cnr.it/ontologies/DLP_397.owl DOLCE-2.1-Lite-Plus] OWL version, including a number of DnS-based modules, has been and is being applied to several ontology projects.A lighter OWL axiomatization of DOLCE and DnS, which also simplifies the names of many classes and properties, adds extensive inline comments, and thoroughly aligns to the repository of Content patterns (available soon as a collaborative design portal) is now available as [http://www.loa-cnr.it/ontologies/DUL.owl DOLCE-Ultralite (abbreviated: DUL)] . Despite its simplification, which greatly speeds up consistency checking and classification of OWL domain ontologies that are plugged to it, the expressivity of DOLCE-Ultralite is not significantly different from the previous DOLCE-Lite-Plus. DOLCE OWL versions, DOLCE-Ultralite and the pattern repository are developed and maintained by Aldo Gangemi [mailto://[e-mail]] and the Rome branch of LOA.

General Formal Ontology (GFO)

The [http://www.onto-med.de/en/theories/gfo/index.html General Formal Ontology] (GFO), developed by [http://www.informatik.uni-leipzig.de/fk/pers/herre.html Heinrich Herre] and his colleagues of the research group [http://www.onto-med.de Onto-Med] in Leipzig, is a realistic ontology integrating processes and objects. It attempts to include many aspects of recent philosophy, which is reflected both in its taxonomic tree and its axiomatizations. GFO allows for different axiomatizations of its categories (such as the existence of atomic time-intervals vs. dense time). The basic principles of GFO are published in the [http://www.onto-med.de/en/publications/scientific-reports/om-report-no8.pdf Onto-Med Report Nr. 8] .

Two GFO specialties, among others, are its account of persistence and its time model. Regarding persistence, the distinction between endurants (objects) and perdurants (processes) is made explicit within GFO by the introduction of a special category, a [http://www.onto-med.de/en/theories/gfo/part1/node20.html persistant] . A persistant is a special category with the intention that its instances "remain identical" (over time). With respect to time, time intervals are taken as primitive in GFO, and time-points (called "time boundaries") as derived. Moreover, time-points may coincide, which is convenient for modelling instantaneous changes.

WordNet

WordNet, a freely available database originally designed as a semantic network based on psycholinguistic principles, was expanded by addition of definitions and is now also viewed as a dictionary. It qualifies as an upper ontology by including the most general concepts as well as more specialized concepts, related to each other not only by the subsumption relations, but by other semantic relations as well, such as part-of and cause. However, unlike Cyc, it has not been formally axiomatized so as to make the logical relations between the concepts precise. It has been widely used in Natural Language Processing research.

uggested Upper Merged Ontology

The Suggested Upper Merged Ontology (SUMO) is another comprehensive ontology project. It includes an upper ontology, created by the IEEE working group P1600.1 (predominantly by Ian Niles and Adam Pease). It is extended with many domain ontologies and a complete set of links to WordNet. It is freely available.

Biomedical ontology

Examples of "domain ontologies" can be found at the Open Biomedical Ontology site. They act as an umbrella organisation for many ontologies specific to biological topics (such as cellular organelles).

* [http://obo.sourceforge.net/ Open Biomedical Ontologies]
* [http://www.bioontology.org/tools/portal/bioportal.html Search, browse and visualise the OBO ontologies online via the NCBO Bioportal]
* [http://oboedit.org/?page=index Ontology browser for most of the Open Biomedical Ontologies]

ee also

* Foundations of mathematics
* Formal Ontology
* Semantic interoperability
* Commonsense knowledge

External links

* [http://www.onto-med.de/en/theories/gfo/index.html General Formal Ontology (GFO) homepage]
* [http://www.loa-cnr.it/ Laboratory of Applied Ontology (LOA) homepage]
* [http://ontolog.cim3.net/cgi-bin/wiki.pl?UpperOntologySummit Upper Ontology Summit (March 2006)]