F.2 BFO – Basic Formal Ontology
The Basic Formal Ontology (BFO) framework developed by Barry Smith and his associates consists of a series of sub-ontologies at different levels of granularity. The ontologies are divided into two varieties: relating to continuant entities such as three-dimensional enduring objects, and occurrent entities (primarily) processes conceived as unfolding in successive phases through 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. A continuant domain ontology descending from BFO can be conceived as an inventory of entities existing at a time. Each occurrent ontology can be conceived as an inventory of processes unfolding through a given interval of time. Both BFO itself and each of its extension subontologies can be conceived as a window on a certain portion of reality at a given level of granularity.
F.2.3 Key characteristics
BFO is a well-documented heavyweight foundational ontology.
It has an interesting horizontal stratification, which is documented in the journey in Figure 28.
Figure 28 – BFO Stratification Journey – six strata (time indexed relations suffixed with ‘… at a time)
This shows an unusual architecture for spacetime. While electing to be separatist about space and time, the TLO also retains spacetime. This results in both spatial and temporal redundancy. Another is the single spatio-temporal reference frame (currently) – see 3.2.1 below.
Single super-sub-type parent-arity for universals – The monohierarchy principle see 2.7 below.
Possibilia: Actualist about worlds – see 3.14 below – that is, no possible worlds. Uses dispositions for some aspects of modality. It is unclear whether it supports a full-blown ontology of modality.
Interpenetration – for example, material and immaterial entities can interpenetrate – a person (material) can stand in a doorway (immaterial) – they are related by having overlapping spatial regions not sharing parts.
Mereology – own version. For example – an immaterial object – the hold of the ship – is a part of the ship, but the material objects in the hold are not part of it, though they are situated in it. Based upon Minimal Extensional Mereology (see below).
Extensible – currently excludes numbers.
F.2.4 Relevant extracts
These extracts from: Basic Formal Ontology 2.0 – SPECIFICATION AND USER’S GUIDE (https://github.com/BFO-ontology/BFO/raw/master/docs/bfo2-reference/BFO2-Reference.pdf).
Extract 1 – Single Inheritance
2.7 The monohierarchy principle
BFO rests on a number of heuristic principles that are designed to advance its utility to formal reasoning. These take the form of simple rules – analogous to the rules of the road – that are designed to promote consistency in the making of both domain-neutral and domain-specific choices in ontology construction.  One heuristic principle of this kind – expressing what we can think of as a principle of good behavior in the realm of universals – asserts that the asserted taxonomies of types and subtypes in BFO-conformant ontologies should be genuine trees (in the graph-theoretic sense), so that each node in the graph of universals should have at most one asserted is_a parent. (On the use of ‘asserted’ here, see .) This principle is of value not only because it supports a simple strategy for the formulation of definitions and thereby helps to prevent certain common kinds of error in ontology construction, but also because it brings technical benefits when ontologies are implemented computationally.
 Barry Smith and Werner Ceusters, “Ontological Realism as a Methodology for Coordinated Evolution of Scientific Ontologies”, Applied Ontology, 5 (2010), 139–188. PMC3104413
Extract 2 – Modality – Actualist
3.7.8 Material basis
Dispositions (and thus also functions) are introduced into BFO in order to provide a means for referring to what we can think of as the potentials or powers of things in the world without the need to quantify over putative ‘possible worlds’ or ‘possible objects’.
Extract 3 – Location – Separatist and Unitist
3.14 Spatiotemporal region
ELUCIDATION: A spatiotemporal region is an occurrent entity that is part of spacetime. [095-001]
‘Spacetime’ here refers to the maximal instance of the universal spatiotemporal region.
3.15 Temporal region
Given a temporal reference frame R, we can define ‘timeR’ as the maximal instance of the universal temporal region.
ELUCIDATION: A temporal region is an occurrent entity that is part of time as defined relative to some reference frame. [100-001]
AXIOM: Every temporal region t is such that t occupies_temporal_region t. [119-002]
AXIOM: All parts of temporal regions are temporal regions. [101-001]
zero-dimensional temporal region
ELUCIDATION: A zero-dimensional temporal region is a temporal region that is without extent. [102-001]
EXAMPLES: a temporal region that is occupied by a process boundary; right now; the moment at which a finger is detached in an industrial accident; the moment at which a child is born, the moment of death.
SYNONYM: temporal instant.
Extract 4 – Location – Reference frames
3.2.1 Excursus on frames
The four dimensions of the spacetime continuum are not homogeneous. Rather there is one time-like and three space-like dimensions. This heterogeneity is sufficient, for the purposes of BFO, to justify our division of reality in a way that distinguishes spatial and temporal regions. In a future version, however, we will need to do justice to the fact that there are multiple ways of dividing up the spacetime continuum into spatial and temporal regions, corresponding to multiple frames that might be used by different observers.
3.6.3 Spatial region
We recommend that users of BFO region terms specify the coordinate frame in terms of which their spatial and temporal data are represented. When dealing with spatial regions on the surface of the Earth, for example, this will be the coordinate frame of latitude and longitude, potentially supplemented by the dimension of altitude.
Extract 5 – Endurantist – Occurrent dependence on Continuants
3.7.2 No s-dependence of higher order
BFO does not recognize universals of higher order (for example, the universal universal). All universals are instantiated by instance entities which are not universals.
Extract 6 – Mereology – Minimal Extensional Mereology
3.1 Relations of parthood
As our starting point in understanding the parthood relation, we take the axioms of Minimal Extensional Mereology as defined by Simons [46, pp. 26-31], assuming, with Simons, the axioms of first order predicate calculus.
Continue to Appendix G: Prior ontological commitment literature