GFO Part I Basic Principles
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16.2 Comparison to Sowa's Ontology

The second comparison is concerned with John Sowa's ontology presented in (54). As his approach is more divergent from ours than DOLCE (cf. figures 3 and 4), we first briefly introduce Sowa's combinatorial approach. After this short introduction, we will discuss the reconstruction of the main distinctions of Sowa's ontology in GFO.

Figure: Hierarchy of Top-level Categories from (54, p. 72)42 .

16.2.1 Introduction: Construction Method

The upper level ontology of John F. Sowa was developed in pursuit of a combinatorial approach based on orthogonal distinctions. This method always generates highly symmetric structures. We confine out analysis to the 27 categories in figure 4, although Sowa discusses further, yet more specific ontological distinctions. The lattice is developed top-down by combining categories that originate from three distinctions: (i) physical vs. abstract, (ii) firstness, secondness, thirdness, (iii) continuant vs. occurrent. We will use the above distinctions as a route for the comparison.

16.2.2 Physical and Abstract Categories

Sowa distinguishes between physical and abstract entities. Following Plato and Whitehead, abstract entities are understood as eternal, mathematical objects, and as such, they do not have a location in space or in time. In contrast to this, physical entities are located in space and time. The relation that holds between physical and abstract entities is that of characterization / representation (in terms of Sowa; our instantiation). An abstract entity characterizes, and is represented, in zero or more physical entities. Sowa observes that the same physical object may be characterized by more than one abstract entity; thus, the relation of characterization / representation is a many-to-many relation.

Intuitively, the notions of physical and abstract entities correspond to the GFO notions of individual and category, respectively. We say that a category is an entity that may be predicated of other entities, and represented by predicative terms. More specifically, we introduce the instantiation relation as a special type of predication, namely as a basic relation between items and immanent universals. Universals, concepts and symbolic structures are not explicitly distinguished in Sowa's ontology. The same holds true for primitive and higher-order categories, where we explicitly allow for categories of a second and even higher order.

We agree with Sowa that one primitive category (abstract) can be predicated of (characterize) several individuals (physical). Also, more than one category can be predicated of a single individual, even if these categories do not stand in a subsumption relation.

The distinction between physical and abstract is the only distinction in Sowa's ontology that he considers context-independent, which is a significant difference with respect to the remaining two differentiations. A physical entity remains physical in all contexts. This also corresponds to our intuitions since, for example, we do not permit individuals to evolve into categories.

16.2.3 Firstness, Secondness and Thirdness

Sowa's ontology is founded on the Peircean notions of firstness, secondness and thirdness. Firstness is introduced as an independent category, which is represented in logic by a monadic predicate $P(x)$, ``which describes some aspect of $x$ without taking into account anything external to $x$'' (54, p. 70). Secondness is a Relative category, which can be represented as a dyadic predicate. Relatives grasp the external relationship to some other entity. Thirdness is a Mediating category that can be represented by means of triadic predicate. The Mediating binds together the Independent and the Relative.

The Peircean distinction is not included explicitly in GFO. Nevertheless it seems that it may be reconstructed in GFO by means of the notions of relators, roles, and players. We interpret relators as mediating category, roles as the relative, and players (independently of that playing) as a category comprising Sowa's independent entities. Let us consider the material relator $z$, founded on some marriage between a man $x$ and a woman $y$. This relator consists of two roles, where the man plays the role of a husband and the woman the role of a wife. Hence, husband and wife - understood as categories on players defined by these roles - are relative categories. Moreover, the particular relator $z$ mediates between $x$ and $y$, through roles as the basis of relative categories of independent entities.

A separate problem is the interpretation of Sowa's category of independents. In the presented example, Woman and Man are subcategories of Independent, which are also material structures. However, one could easily argue that they are not independent, as it is required in Sowa's ontology. The most independent entities from the point of view of GFO are situations and situoids, hence only these might be interpreted as independent entities in Sowa's terms. However, we feel that this interpretation would be too restrictive, and adopt the view that Independent in Sowa includes a cross-cutting collection of GFO categories, among them material structures, processes, chronoids and others.

16.2.4 Continuants and Occurrents

Sowa defines continuants and occurrents as follows:

``A continuant has stable attributes or characteristics that enable its various appearances at different times to be recognized as the same individual.

An occurrent is in a state of flux that prevents it from being recognized by a stable set of attributes. Instead, it can only be identified by its location in some region of space-time.'' (54, p. 71)

Moreover, Sowa remarks that the continuant categories are characterized by a predicate that does not involve time or a time like succession, while occurrents are characterized by a predicate that depends on time or a time like succession. One can observe that the notions of continuant and their appearances correspond fairly well to our combination of persistant and presential. Persistants provide the principle of identity to the presentials instantiating them. Furthermore, persistants as universals are not directly related to time and space. However, attribute assignments to persistants in the sense of referring to stable attributes of their presentials should be grasped in terms of relations between persistants and property universals. Further, presentials may not necessarily share a stable set of properties to be identified as the appearances of the same entity. Ontological identity is provided in GFO not by the exhibition of ``the same'' qualities, but by ontically connected instances of the same persistant.

The occurrent category of Sowa, on the one hand, appears to correspond to our notions of processes. In GFO, processes are entities that develop over time, unfold in time or perdure. Processes are related to time regions by the projection relation, which seems similar to demanding the identification of occurrents by their location in some region of space-time. Note that this location in space-time can only apply to individual processes, at least in GFO terms. On the other hand, Sowa's occurrents may be interpreted as GFO occurrents, if figure 4 is considered. The specialization of occurrent into, among others, process, history and situation is similar to the GFO categories of processes, histories, and situoids. In summary, we find it more appropriate to map Sowa's occurrents into GFO occurrents rather than processes.

16.2.5 Combination of the Distinctions

The combination of the above three distinctions made by Sowa results in six intermediate and twelve leaf categories.43 The preliminary and intuitive mapping of those with GFO categories is presented in the tables 4 and 5 (p. [*] and [*]). We observe that each of Sowa's categories appears reconstructible in GFO, except for three of them, namely: Intention, Reason and Purpose. The reason for this is that GFO is based on the theory of levels, but the mental and social levels to which the notions of intention, reason and purpose belong are only indicative.

16.2.6 Conclusion

We have presented the interpretation of the main distinctions of Sowa's ontology in GFO. Further, an intuitive mapping of GFO and Sowa's categories is provided in tabular form. We observe that all of Sowa's categories except for three can be reinterpreted in GFO. However, mapping in the opposite direction seems to be more problematic. For many of our categories, we have not found the corresponding notions in Sowa's ontology. Although deeply analyzed in (54), neither a space-time model nor a property model is included in Sowa's ontology.44

In general, the construction method of GFO is not as strictly combinatorial as is Sowa's ontology. Indeed, most of the categories of GFO do not have a combinatorial character. Apart from that, the actual structure of GFO categories is a (less symmetric) lattice. Note that the category tree presented on page [*] is a simplification, for the purpose of conveying first intuitions to the reader.

Table 4: Mapping Selected GFO Categories to John Sowa's Categories (roughly).
GFO Ontology of John Sowa
Entity Entity
Set (below Schema)
Item -
Category Abstract
Immanent Universal -
Persistant (Continuant)
Concept -
Symbolic Structure (below Schema)
Individual -
Space-Time-Entity -
Chronoid -
Time-Boundary -
Region -
Spatial Boundary -
Abstract Individual -
Concrete Individual Physical
Presential (Continuant)
Material Structure -
Material Object (Object)
Material Boundary -
Configuration -
Simple Configuration -
Situation -
Fact -
Occurrent Occurrent
Process Process
Continuous Process -
Discrete Process -
State -
Configuroid -
Situoid -
Change -
Instantaneous Change -
Continuous Change -
Property -
Property Value -
Relator (Mediating)
Material Relator -
Formal Relator -

Table 5: Mapping John Sowa's to GFO categories (roughly). Note that this mapping is provided with reservations, and detailed explanations of the individual mappings remain to be stated.
Ontology of John Sowa GFO
Entity Entity
Independent (Situoid)
Physical Individual (intuitively); Presential (by axioms)
Relative (Universal defined by a relational role universal)
Abstract Category
Mediating Relation
Continuant (Presential Persistant)
Occurrent Occurrent
Actuality (Material structure Process)
Form (Category of material structures or process)
Prehension (Material structure in a role)
Proposition (Instantiation)
Nexus (Relator or foundation of a relator)
Intention -
Object Material structure Persistant
Process Process
Schema Category of material structures
Script Category of processes
Juncture (Relational role)
Participation (Processual role)
Description Symbolic structure of material structures
History Symbolic structure of histories
Situation (Structure) (Material structure as a foundation of a relator)
Execution (Situation) (Process as a foundation of a relator)
Reason -
Purpose -

Robert Hoehndorf 2006-10-18


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