Information technology — Top-level ontologies (TLO) — Part 2: Basic Formal Ontology (BFO)

This document describes Basic Formal Ontology (BFO), which is an ontology that is conformant to the requirements specified for top-level ontologies in ISO/IEC 21838‑1. It describes BFO as a resource designed to support the interchange of information among heterogeneous information systems. The following are within the scope of this document: — definitions of BFO-2020 terms and relations; — axiomatizations of BFO-2020 in OWL 2 and CL; — documentation of the conformity of BFO-2020 to the requirements specified for top-level ontologies in ISO/IEC 21838‑1; — specification of the requirements for a domain ontology if it is to serve as a module in a suite of ontologies in which BFO serves as top-level ontology hub by providing a starting point for the introduction of the most general terms in those domain ontologies which are its nearest neighbours within the suite; — specification of the role played by the terms in BFO in the formulation of definitions and axioms in ontologies at lower levels that conform to BFO. The following are outside the scope of this document: — specification of ontology languages, including the languages RDF, OWL, and CL standardly used in ontology development; — specification of methods for reasoning with ontologies; — specification of translators between the notations of ontologies developed in different ontology languages.

Technologies de l'information — Ontologies de haut-niveau (TLO) — Partie 2: Ontologie formelle de base (BFO)

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Published
Publication Date
29-Nov-2021
Current Stage
6060 - International Standard published
Start Date
02-Mar-2020
Completion Date
30-Nov-2021
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INTERNATIONAL ISO/IEC
STANDARD 21838-2
First edition
2021-11
Information technology — Top-level
ontologies (TLO) —
Part 2:
Basic Formal Ontology (BFO)
Technologies de l'information — Ontologies de haut-niveau (TLO) —
Partie 2: Ontologie formelle de base (BFO)
Reference number
ISO/IEC 21838-2:2021(E)
© ISO/IEC 2021
---------------------- Page: 1 ----------------------
ISO/IEC 21838-2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO/IEC 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC 21838-2:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Conformity of BFO-2020 to ISO/IEC 21838-1 ......................................................................................................................... 3

4.1 Overview ...................................................................................................................................................................................................... 3

4.2 Natural language representation of BFO-2020 .......................................................................................................... 3

4.3 OWL 2 formalization of BFO-2020 ........................................................................................................................................ 3

4.4 Common Logic axiomatization of BFO-2020 ................................................................................................................ 3

4.4.1 General ........................................................................................................................................................................................ 3

4.4.2 Modularity ............................................................................................................................................................................... 4

4.5 Specification of the purpose of BFO (in conformance with ISO/IEC 21838-1:2021,

4.4.2) ................................................................................................................................................................................................................ 4

4.5.1 General ........................................................................................................................................................................................ 4

4.5.2 Example Open Biomedical Ontologies (OBO) ............................................................................................ 4

4.5.3 Example Common Core Ontologies (CCO) .................................................................................................... 4

4.6 Description of how conformance of a domain ontology to BFO is established (in

conformance with ISO/IEC 21838-1:2021, 4.4.3)..................................................................................................... 5

4.6.1 Overview ................................................................................................................................................................................... 5

4.6.2 Conformance through direct extension......................................................................................................... 5

4.6.3 Conformance through indirect extension.................................................................................................... 6

4.6.4 Conformance through re-engineering ............................................................................................................ 6

4.6.5 Validating conformance to BFO ............................................................................................................................ 6

4.7 Specification of how consistency of the CL axiomatization of BFO-2020 is

demonstrated (in conformance with ISO/IEC 21838-1:2021, 4.4.4) ....................................................... 6

4.7.1 Overview ................................................................................................................................................................................... 6

4.7.2 Documentation..................................................................................................................................................................... 7

4.7.3 Structure of the model .................................................................................................................................................. 7

4.8 Description of how interpretability of the OWL 2 axiomatization of BFO-2020 in

the CL axiomatization is established (in conformance with ISO/IEC 21838-1:2021,

4.4.5) ................................................................................................................................................................................................................ 7

4.8.1 Interpretability proof strategy for BFO-2020-OWL ........................................................................... 7

4.8.2 Interpretability for alternative axiomatizations of BFO-2020 .................................................. 8

4.9 Demonstration of breadth of coverage of BFO (in conformance with with ISO/IEC

21838-1:2021, 4.4.6) .......................................................................................................................................................................... 9

4.9.1 General ........................................................................................................................................................................................ 9

4.9.2 Space and time ...................................................................... ................................................................................................ 9

4.9.3 Actuality and possibility ............................................................................................................................................. 9

4.9.4 Classes and types ............................................................................................................................................................... 9

4.9.5 Change over time ............................................................................................................................................................... 9

4.9.6 Parts, wholes, unity and boundaries ............................................................................................................. 10

4.9.7 Space and place ................................................................................................................................................................. 10

4.9.8 Scale and granularity .................................................................................................................................................. 10

4.9.9 Qualities and other attributes ............................................................................................................................. 10

4.9.10 Quantities and mathematical entities .......................................................................................................... 10

4.9.11 Processes and events ................................................................................................................................................... 11

4.9.12 Constitution ......................................................................................................................................................................... 11

4.9.13 Causality ................................................................................................................................................................................. 11

4.9.14 Information and reference...................................................................................................................................... 11

4.9.15 Artefacts and socially constructed entities ............................................................................................ 11

4.9.16 Mental entities; imagined entities; fiction; mythology; religion ..........................................12

iii
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ISO/IEC 21838-2:2021(E)
4.10 Documentation of ontology management principles (in conformance with ISO/

IEC 21838-1:2021, 4.4.8) .............................................................................................................................................................12

Bibliography .............................................................................................................................................................................................................................13

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ISO/IEC 21838-2:2021(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are

members of ISO or IEC participate in the development of International Standards through technical

committees established by the respective organization to deal with particular fields of technical

activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international

organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the

work.

The procedures used to develop this document and those intended for its further maintenance

are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria

needed for the different types of document should be noted. This document was drafted in

accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives or

www.iec.ch/members_experts/refdocs).

Attention is drawn to the possibility that some of the elements of this document may be the subject

of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent

rights. Details of any patent rights identified during the development of the document will be in the

Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC

list of patent declarations received (see https://patents.iec.ch).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see

www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.

This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 32, Data management and interchange.

A list of all parts in the ISO/IEC 21838 series can be found on the ISO and IEC websites.

Any feedback or questions on this document should be directed to the user’s national standards

body. A complete listing of these bodies can be found at www.iso.org/members.html and

www.iec.ch/national-committees.
© ISO/IEC 2021 – All rights reserved
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ISO/IEC 21838-2:2021(E)
Introduction

Basic Formal Ontology (BFO) is a top-level ontology (TLO) conforming to ISO/IEC 21838-1. It contains

(i) definitions of its terms and relational expressions and (ii) formalizations in OWL 2 and in Common

Logic (CL). BFO is a public-domain resource introduced in 2002. It is an ontology of highly general terms

designed to support the interoperability of data and information systems associated with ontologies

containing more specific terms relating to specific domains. The primary goal of BFO is to support

the development of such domain ontologies in a way that promotes the coordination of ontology

development by different groups in a way that promotes consistency and non-redundancy. BFO was

initially conceived as part of a strategy to advance coordinated domain ontology development across

the life sciences. BFO has since been used for similar purposes in other areas, including data and

information science, sustainable development, and in the engineering, military and intelligence fields.

This document was developed as a response to the need for a TLO designed to support information

system interoperability expressed by ontology users in these and other areas.

BFO is a domain-neutral ontology. This means that it provides terms representing only highly general

categories – such as object, quality, process, spatial and temporal region – which pertain to all domains

of reality.
BFO has existed thus far in four major release versions.
Version 1.0 (released in 2002)
Version 1.1 (released in 2007)
[7]
Version 2.0 (released in 2015)
[10] [11]
Version 2020 (released in 2020) ,

Through these successive versions the categorial core of BFO, resting on a distinction between

continuants and occurrents, and between dependent and independent entities, has remained constant.

Version 1.1 added the new category of generically dependent continuant, which was introduced to

provide a starting point for definitions of terms representing information artefacts and other dependent

entities (such as nucleic acid sequences) which can exist in multiple copies. Version 2.0 differs from its

predecessors in a series of minor changes which flowed from a major re-formalization using the OWL 2

[3]
language .

The BFO-2020 category hierarchy is illustrated in Figure 1. This extends the category hierarchy of

BFO 2.0 through the inclusion of two terms (“temporal instant” and “temporal interval”) and through

the renaming of terms relating to fiat boundaries. BFO-2020 also adds a systematic repertoire of inverse

relations to the relations in BFO 2.0 and an enriched treatment of relations involving time.

BFO-2020-Terms, the natural language specification of BFO-2020, supports human maintenance and

use of the ontology, including use in development of BFO-conformant domain ontologies.

BFO-2020-OWL, the OWL 2 formalization of BFO-2020, supports use of the ontology in computing,

including enabling BFO-2020 to be used in tandem with other ontologies expressed in OWL and in

related languages, and in allowing ontology quality control through use of OWL reasoners.

BFO-2020-CL, the CL formalization of BFO-2020, provides the expressivity needed to capture the formal

structures used by BFO-2020, for example in its treatment of time, space and parthood.

This document conforms to ISO/IEC 21838-1.
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ISO/IEC 21838-2:2021(E)
Figure 1 — BFO-2020 is_a hierarchy
vii
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INTERNATIONAL STANDARD ISO/IEC 21838-2:2021(E)
Information technology — Top-level ontologies (TLO) —
Part 2:
Basic Formal Ontology (BFO)
1 Scope

This document describes Basic Formal Ontology (BFO), which is an ontology that is conformant to the

requirements specified for top-level ontologies in ISO/IEC 21838-1.

It describes BFO as a resource designed to support the interchange of information among heterogeneous

information systems. The following are within the scope of this document:
— definitions of BFO-2020 terms and relations;
— axiomatizations of BFO-2020 in OWL 2 and CL;

— documentation of the conformity of BFO-2020 to the requirements specified for top-level ontologies

in ISO/IEC 21838-1;

— specification of the requirements for a domain ontology if it is to serve as a module in a suite of

ontologies in which BFO serves as top-level ontology hub by providing a starting point for the

introduction of the most general terms in those domain ontologies which are its nearest neighbours

within the suite;

— specification of the role played by the terms in BFO in the formulation of definitions and axioms in

ontologies at lower levels that conform to BFO.
The following are outside the scope of this document:

— specification of ontology languages, including the languages RDF, OWL, and CL standardly used in

ontology development;
— specification of methods for reasoning with ontologies;

— specification of translators between the notations of ontologies developed in different ontology

languages.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO/IEC 21838-1:2021, Information technology — Top-level ontologies (TLO) — Part 1: Requirements

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/IEC 21838-1 and the following

apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
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ISO/IEC 21838-2:2021(E)
— IEC Electropedia: available at http:// www .electropedia .org/

NOTE The following terms and definitions, along with the definitions in ISO/IEC 21838-1, form part of the

meta-vocabulary used for describing BFO-2020 in this document, except that in BFO the terms "entity" and

"object" are not synonyms. The vocabulary of BFO-2020 itself is documented in https:// standards .iso .org/ iso

-iec/ 21838/ -2/ ed -1/ en.
3.1
primitive
expression for which no non-circular definition can be provided
3.2
universal
type
entity (3.1) that has indefinitely many instances (3.6)

EXAMPLE Electron, molecule, cell, planet, explosion, vehicle, hour, traffic law, organization, mortgage

contract, email message.

Note 1 to entry: References to universals are employed in the formulation of the assertions of natural science

and of analogous general assertions in technical manuals, experimental protocols or legal or administrative

documents.
3.3
extension
collection (3.4) of instances of a universal (3.2)

Note 1 to entry: In OWL, every Class is associated with a Class Extension, which is the set of Instances of the Class.

In Reference [4] (from 2004), it is asserted that: "A class has an intensional meaning (the underlying concept)

which is related but not equal to its class extension. Thus, two classes may have the same class extension, but still

be different classes."
3.4
collection
group of particulars
Note 1 to entry: The particulars in a collection are called its members.

Note 2 to entry: The term "collection" is to be understood as allowing change of members over time (see

ISO/IEC 21838-1:2021, B.3.2).
3.5
defined class

collection (3.4), whose members are defined by specifying a restriction on one or more universals (3.2),

that is not the extension (3.3) of any universal (3.2)

EXAMPLE Non-smoker (meaning: person who does not smoke); pet (meaning: animal that is kept for

companionship or pleasure); mortgagee (meaning: person with a mortgage); lathe operator (meaning: person

with an employment role realized through operating a lathe); target (meaning: thing or process that is targeted).

Note 1 to entry: In the OWL 2 community the expression "Defined Class" is sometimes used informally to refer to

those Classes in an ontology in which both necessary and sufficient conditions are provided, as contrasted with

what are called "Primitive Classes" for which only necessary conditions are provided.

3.6
instance
particular that instantiates some universal (3.2)
EXAMPLE John, John’s laptop, the year 2012.
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ISO/IEC 21838-2:2021(E)
4 Conformity of BFO-2020 to ISO/IEC 21838-1
4.1 Overview

BFO-2020 has three elements, the documentation of which is provided at https:// standards .iso .org/ iso

-iec/ 21838/ -2/ ed -1/ en:

a) natural language representation of its terms, relational expressions and definitions;

b) formalization in OWL 2 (Web Ontology Language);
c) formalization in CL (Common Logic).

NOTE As pointed out in ISO/IEC 21838-1:2021, 4.2.2, alternative OWL axiomatizations of BFO-2020 can be

conformant to BFO-2020-CL. On the treatment of such alternative axiomatizations, see 4.8.2.

4.2 Natural language representation of BFO-2020

The natural language representation of BFO-2020, provided in the file BFO-2020-Terms provided

at https:// standards .iso .org/ iso -iec/ 21838/ -2/ ed -1/ en/ establishes conformity of BFO-2020 to

ISO/IEC 21838-1:2021, 4.1.
4.3 OWL 2 formalization of BFO-2020

The OWL 2 formalization of BFO-2020, provided in the file BFO-2020-OWL (https:// standards .iso .org/

iso -iec/ 21838/ -2/ ed -1/ en) establishes conformance to ISO/IEC 21838-1:2021, 4.2. BFO-2020-OWL

consists of the following parts:
4.3.1 BFO-2020.owl – OWL in rdf format.
[8]
4.3.2 BFO-2020.ofn – OWL in functional syntax with URIs.

4.3.3 BFO-2020-labelled.ofn – OWL in functional syntax with labels instead of URIs.

4.3.4 BFO-2020-iris.xlsx – table of IRIs for all classes and relations in BFO-2020-CL, including all

classes and relations in BFO-2020-OWL.

4.3.5 bfo-relations-table.xlsx – table showing all relations in BFO-2020 including all inverses and all

binary variants used in BFO-2020-OWL.

4.3.6 temporalized-definitions.cl – the set of CL definitions of binary at-all-times/some-time

relations used in BFO-2020-OWL.

4.3.7 temporalized-definitions.prover9 – the set of definitions of binary at-all-times/some-time

[2]
relations used in OWL (as for 4.3.3) but in prover9 format .
4.4 Common Logic axiomatization of BFO-2020
4.4.1 General

The CL formalization of BFO-2020 (provided at https:// standards .iso .org/ iso -iec/ 21838/ -2/ ed -1/ en) to

ISO/IEC 21838-1:2021, 4.3, BFO-2020-CL is provided in the following formats:

a) axiomatization in Common Logic Interchange Format (CLIF) as specified in ISO/IEC 24707 is

provided in the common-logic directory;
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ISO/IEC 21838-2:2021(E)

b) axiomatization using prolog style variables for ingestion in the prover9 automated theorem prover

is documented in Reference [2] is provided in the prover9 directory;

c) axiomatization in standard first-order predicate logic notation is provided in the pdf directory.

4.4.2 Modularity

The axioms in BFO-2020-CL are divided into the following sections in conformance with the requirement

of explicit modularization at ISO/IEC 21838-1:2021, 4.1.
Continuant Mereology Order
Domain and Range Participation
Existence and Instantiation Spatial Region
Generic Dependence Spatiotemporal Region
History Specific Dependency
Material Entity Temporal Region
Occurrent Mereology Universal Declaration

4.5 Specification of the purpose of BFO (in conformance with ISO/IEC 21838-1:2021,

4.4.2)
4.5.1 General

BFO is designed as a top-level ontology that can serve as a starting point for definitions in suites of

domain ontologies in conformance with ISO/IEC 21838-1:2021, 4.4.2. Examples of such suites using BFO

in this manner are provided in 4.5.2 and 4.5.3.
4.5.2 Example Open Biomedical Ontologies (OBO)
Bacterial Clinical Infectious Diseases Ontology Mental Disease Ontology (MFOMD)
(BCIDO)
Beta Cell Genomics Application Ontology (BCGO) Mental Functioning Ontology (MFO)
Biological Collections Ontology (BCO) Ontology for Adverse Events (OAE)
Cell Ontology (CL) Ontology for Biobanking (OBIB)
Cell Line Ontology (CLO) Ontology of Biological and Clinical Statistics (OBCS)

Chemical Entities of Biological Interest (CHEBI) Ontology for Biomedical Investigations (OBI)

Common Anatomy Reference Ontology (CARO) Ontology for General Medical Science (OGMS)

Drug Ontology (DRON) Ontology of Medically Related Social Entities (OMRSE)
Emotion Ontology (MFOEM) Oral Health and Disease Ontology (OHD)
Environment Ontology (ENVO) Plant Ontology (PO)
Gene Ontology (GO) Population and Community Ontology (PCO)
Human Disease Ontology (HDO) Protein Ontology (PRO)
Infectious Disease Ontology (IDO) Relations Ontology (RO)
Information Artefact Ontology (IAO) Vaccine Ontology (VO)
[5]

Documentation of these and other OBO Foundry ontologies is provided at http:// obofoundry .org .

4.5.3 Example Common Core Ontologies (CCO)
Agent Ontology Information Entity Ontology
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ISO/IEC 21838-2:2021(E)
Artefact Ontology Modal Relation Ontology
Currency Unit Ontology Quality Ontology
Event Ontology Time Ontology
Extended Relation Ontology Units of Measure Ontology
Geospatial Ontology
The CCO suite is extended by a series of application ontologies, including:
Aircraft Ontology Mission Planning Ontology
Airforce Aircraft Maintenance Ontology Occupation Ontology
Army Universal Task List Ontology Outer Space Ontology
Airforce Aircraft Maintenance Ontology Physiographic Feature Ontology
Army Universal Task List Ontology Sensor Ontology
Emotion Ontology Skills Ontology
Hydrographic Feature Ontology Space Object Ontology
Legal and Criminal Act Ontology Transportation Infrastructure Ontology
Military Operations Ontology Undersea Warfare Ontology
Mission Planning Ontology Watercraft Ontology

Documentation of these and other common core ontologies is provided in Reference [6].

4.6 Description of how conformance of a domain ontology to BFO is established (in

conformance with ISO/IEC 21838-1:2021, 4.4.3)
4.6.1 Overview

Where BFO serves as starting point for the development, or for the re-engineering, of domain ontologies

or other external ontology resources, the conformance of the latter to BFO in conformance with

ISO/IEC 21838-1:2021, 4.4.3 is established in the following ways.
4.6.2 Conformance through direct extension

One common strategy used to ensure conformance of a domain ontology to BFO is to load BFO into

an ontology editor and construct the domain ontology ab initio on this basis. Terms in BFO are then

used as starting point for defining the topmost set of domain ontology terms as specializations of the

relevant BFO categories. Categories shall be used for this purpose that are at the lowest level in the BFO

hierarchy suitable for the purposes of the domain ontology, and in any case at a level below "entity".

Conformance for a domain ontology constructed in this way requires:

a) that the result of adding the domain ontology terms and relational expressions to BFO is a consistent

ontology.
In addition, it requires that each term in the domain ontology is either:
b1) connected to BFO via some unique chain of is_a relations, or

b2) able to be defined through some logical combinations of terms satisfying b1) but not itself such as

to satisfy b1).
In the latter case, the term refers to a defined class (see definition 3.5).
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ISO/IEC 21838-2:2021(E)

The requirement of uniqueness in b1) implies that all terms in the resulting ontology that refer to

universals (in the sense of definition 3.2), rather than to defined classes, form a hierarchy governed by

single inheritance (no term in the resulting ontology shall have more than one parent).

Adding a domain ontology to BFO, in some cases, results in a conservative extension of BFO (thus no

more theorems using only terms and relational expressions in the signature of BFO will be provable

using BFO extended by the domain ontology than are provable using BFO alone). In cases where the

domain ontology relates to universals – for example time and space in a physics ontology – which are

BFO categories, then the result might not be a conservative extension for example because it contains a

more granular treatment of time and space than is provided by BFO.
4.6.3 Conformance thr
...

FINAL
INTERNATIONAL ISO/IEC
DRAFT
STANDARD FDIS
21838-2.2
ISO/IEC JTC 1/SC 32
Information technology — Top-level
Secretariat: ANSI
ontologies (TLO) —
Voting begins on:
2021-06-14
Part 2:
Voting terminates on:
Basic Formal Ontology (BFO)
2021-08-09
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/IEC FDIS 21838-2.2:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO/IEC 2021
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ISO/IEC FDIS 21838-2.2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2021 – All rights reserved
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ISO/IEC FDIS 21838-2.2:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Conformity of BFO-2020 to ISO/IEC 21838-1 ......................................................................................................................... 3

4.1 Overview ...................................................................................................................................................................................................... 3

4.2 Natural language representation of BFO-2020 ........................................................................................................... 3

4.3 OWL 2 formalization of BFO-2020 ........................................................................................................................................ 3

4.4 Common Logic axiomatization of BFO-2020 ................................................................................................................ 3

4.4.1 General...................................................................................................................................................................................... 3

4.4.2 Modularity ............................................................................................................................................................................. 4

4.5 Specification of the purpose of BFO (in conformance with ISO/IEC 21838-1:—, 4.4.2) ........ 4

4.5.1 General...................................................................................................................................................................................... 4

4.5.2 Example Open Biomedical Ontologies (OBO) ......................................................................................... 4

4.5.3 Example Common Core Ontologies (CCO) ................................................................................................. 5

4.6 Description of how conformance of a domain ontology to BFO is established (in

conformance with ISO/IEC 21838-1:—, 4.4.3) ........................................................................................................... 5

4.6.1 Overview ................................................................................................................................................................................. 5

4.6.2 Conformance through direct extension ....................................................................................................... 5

4.6.3 Conformance through indirect extension................................................................................................... 6

4.6.4 Conformance through re-engineering ........................................................................................................... 6

4.6.5 Validating conformance to BFO ........................................................................................................................... 6

4.7 Specification of how consistency of the CL axiomatization of BFO-2020 is

demonstrated (in conformance with ISO/IEC 21838-1:—, 4.4.4).............................................................. 7

4.7.1 Overview ................................................................................................................................................................................. 7

4.7.2 Documentation .................................................................................................................................................................. 7

4.7.3 Structure of the model ................................................................................................................................................ 7

4.8 Description of how interpretability of the OWL 2 axiomatization of BFO-2020 in

the CL axiomatization is established (in conformance with ISO/IEC 21838-1:—, 4.4.5) ...... 7

4.8.1 Interpretability proof strategy for BFO-2020-OWL .......................................................................... 7

4.8.2 Interpretability for alternative axiomatizations of BFO-2020 ................................................. 8

4.9 Demonstration of breadth of coverage of BFO (in conformance with with ISO/IEC

21838-1:—, 4.4.6) ................................................................................................................................................................................ 9

4.9.1 General...................................................................................................................................................................................... 9

4.9.2 Space and time ................................................................................................................................................................... 9

4.9.3 Actuality and possibility ............................................................................................................................................ 9

4.9.4 Classes and types ............................................................................................................................................................. 9

4.9.5 Change over time ..........................................................................................................................................................10

4.9.6 Parts, wholes, unity and boundaries............................................................................................................10

4.9.7 Space and place ..............................................................................................................................................................10

4.9.8 Scale and granularity.................................................................................................................................................10

4.9.9 Qualities and other attributes ...........................................................................................................................10

4.9.10 Quantities and mathematical entities .........................................................................................................11

4.9.11 Processes and events ................................................................................................................................................11

4.9.12 Constitution .......................................................................................................................................................................11

4.9.13 Causality ...............................................................................................................................................................................11

4.9.14 Information and reference ...................................................................................................................................11

4.9.15 Artefacts and socially constructed entities ............................................................................................12

4.9.16 Mental entities; imagined entities; fiction; mythology; religion ..........................................12

4.10 Documentation of ontology management principles (in conformance with ISO/

IEC 21838-1:—, 4.4.8) ...................................................................................................................................................................12

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Bibliography .............................................................................................................................................................................................................................13

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ISO/IEC FDIS 21838-2.2:2021(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are

members of ISO or IEC participate in the development of International Standards through technical

committees established by the respective organization to deal with particular fields of technical

activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international

organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the

work.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for

the different types of document should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject

of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent

rights. Details of any patent rights identified during the development of the document will be in the

Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC

list of patent declarations received (see patents.iec.ch).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 32, Data management and interchange.
A list of all parts in the ISO/IEC 21838 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO/IEC FDIS 21838-2.2:2021(E)
Introduction

Basic Formal Ontology (BFO) is a top-level ontology (TLO) conforming to ISO/IEC 21838-1:—. It

contains (i) definitions of its terms and relational expressions and (ii) formalizations in OWL 2 and

in Common Logic (CL). BFO is a public-domain resource introduced in 2002. It is an ontology of highly

general terms designed to support the interoperability of data and information systems associated

with ontologies containing more specific terms relating to specific domains. The primary goal of BFO

is to support the development of such domain ontologies in a way that promotes the coordination of

ontology development by different groups in a way that promotes consistency and non-redundancy.

BFO was initially conceived as part of a strategy to advance coordinated domain ontology development

across the life sciences. BFO has since been used for similar purposes in other areas, including data and

information science, sustainable development, and in the engineering, military and intelligence fields.

This document was developed as a response to the need for a TLO designed to support information

system interoperability expressed by ontology users in these and other areas.

BFO is a domain-neutral ontology. This means that it provides terms representing only highly general

categories – such as object, quality, process, spatial and temporal region – which pertain to all domains

of reality.
BFO has existed thus far in four major release versions.
Version 1.0 (released in 2002)
Version 1.1 (released in 2007)
[7]
Version 2.0 (released in 2015)
[10] [11]
Version 2020 (released in 2020) ,

Through these successive versions the categorial core of BFO, resting on a distinction between

continuants and occurrents, and between dependent and independent entities, has remained constant.

Version 1.1 added the new category of generically dependent continuant, which was introduced to

provide a starting point for definitions of terms representing information artefacts and other dependent

entities (such as nucleic acid sequences) which can exist in multiple copies. Version 2.0 differs from its

predecessors in a series of minor changes which flowed from a major re-formalization using the OWL 2

[3]
language .

The BFO-2020 category hierarchy is illustrated in Figure 1. This extends the category hierarchy of

BFO 2.0 through the inclusion of two terms ("temporal instant" and "temporal interval") and through

the renaming of terms relating to fiat boundaries. BFO-2020 also adds a systematic repertoire of inverse

relations to the relations in BFO 2.0 and an enriched treatment of relations involving time.

BFO-2020-Terms, the natural language specification of BFO-2020, supports human maintenance and

use of the ontology, including use in development of BFO-conformant domain ontologies.

BFO-2020-OWL, the OWL 2 formalization of BFO-2020, supports use of the ontology in computing,

including enabling BFO-2020 to be used in tandem with other ontologies expressed in OWL and in

related languages, and in allowing ontology quality control through use of OWL reasoners.

BFO-2020-CL, the CL formalization of BFO-2020, provides the expressivity needed to capture the formal

structures used by BFO-2020, for example in its treatment of time, space and parthood.

This document conforms to ISO/IEC 21838-1.

1) Under preparation. Stage at the time of publication: ISO/IEC PRF 21838-1:2021.

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ISO/IEC FDIS 21838-2.2:2021(E)
Figure 1 — BFO-2020 is_a hierarchy
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FINAL DRAFT INTERNATIONAL STANDARD ISO/IEC FDIS 21838-2.2:2021(E)
Information technology — Top-level ontologies (TLO) —
Part 2:
Basic Formal Ontology (BFO)
1 Scope

This document describes Basic Formal Ontology (BFO), which is an ontology that is conformant to the

requirements specified for top-level ontologies in ISO/IEC 21838-1.

It describes BFO as a resource designed to support the interchange of information among heterogeneous

information systems. The following are within the scope of this document:
— definitions of BFO-2020 terms and relations;
— axiomatizations of BFO-2020 in OWL 2 and CL;

— documentation of the conformity of BFO-2020 to the requirements specified for top-level ontologies

in ISO/IEC 21838-1;

— specification of the requirements for a domain ontology if it is to serve as a module in a suite of

ontologies in which BFO serves as top-level ontology hub by providing a starting point for the

introduction of the most general terms in those domain ontologies which are its nearest neighbours

within the suite;

— specification of the role played by the terms in BFO in the formulation of definitions and axioms in

ontologies at lower levels that conform to BFO.
The following are outside the scope of this document:

— specification of ontology languages, including the languages RDF, OWL, and CL standardly used in

ontology development;
— specification of methods for reasoning with ontologies;

— specification of translators between the notations of ontologies developed in different ontology

languages.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO/IEC 21838-1:—, Information technology — Top-level ontologies (TLO) — Part 1: Requirements

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/IEC 21838-1 and the following

apply.

2) Under preparation. Stage at the time of publication: ISO/IEC PRF 21838-1:2021.

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ISO/IEC FDIS 21838-2.2:2021(E)

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/

NOTE The following terms and definitions, along with the definitions in ISO/IEC 21838-1, form part of the

meta-vocabulary used for describing BFO-2020 in this document, except that in BFO the terms "entity" and

"object" are not synonyms. The vocabulary of BFO-2020 itself is documented in https:// standards .iso .org/ iso

-iec/ 21838/ -2/ ed -1/ en.
3.1
primitive
expression for which no non-circular definition can be provided
3.2
universal
type
entity (3.1) that has indefinitely many instances (3.6)

EXAMPLE Electron, molecule, cell, planet, explosion, vehicle, hour, traffic law, organization, mortgage

contract, email message.

Note 1 to entry: References to universals are employed in the formulation of the assertions of natural science

and of analogous general assertions in technical manuals, experimental protocols or legal or administrative

documents.
3.3
extension
collection (3.4) of instances of a universal (3.2)

Note 1 to entry: In OWL, every Class is associated with a Class Extension, which is the set of Instances of the Class.

In Reference [4] (from 2004), it is asserted that: "A class has an intensional meaning (the underlying concept)

which is related but not equal to its class extension. Thus, two classes may have the same class extension, but still

be different classes."
3.4
collection
group of particulars
Note 1 to entry: The particulars in a collection are called its members.

Note 2 to entry: The term "collection" is to be understood as allowing change of members over time (see

ISO/IEC 21838-1:—, B.3.2).
3.5
defined class

collection (3.4), whose members are defined by specifying a restriction on one or more universals (3.2),

that is not the extension (3.3) of any universal (3.2)

EXAMPLE Non-smoker (meaning: person who does not smoke); pet (meaning: animal that is kept for

companionship or pleasure); mortgagee (meaning: person with a mortgage); lathe operator (meaning: person

with an employment role realized through operating a lathe); target (meaning: thing or process that is targeted).

Note 1 to entry: In the OWL 2 community the expression "Defined Class" is sometimes used informally to refer to

those Classes in an ontology in which both necessary and sufficient conditions are provided, as contrasted with

what are called "Primitive Classes" for which only necessary conditions are provided.

3.6
instance
particular that instantiates some universal (3.2)
EXAMPLE John, John’s laptop, the year 2012.
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4 Conformity of BFO-2020 to ISO/IEC 21838-1
4.1 Overview

BFO-2020 has three elements, the documentation of which is provided at https:// standards .iso .org/ iso

-iec/ 21838/ -2/ ed -1/ en:

a) natural language representation of its terms, relational expressions and definitions;

b) formalization in OWL 2 (Web Ontology Language);
c) formalization in CL (Common Logic).

NOTE As pointed out in ISO/IEC 21838-1:—, 4.2.2, alternative OWL axiomatizations of BFO-2020 can be

conformant to BFO-2020-CL. On the treatment of such alternative axiomatizations, see 4.8.2.

4.2 Natural language representation of BFO-2020

The natural language representation of BFO-2020, provided in the file BFO-2020-Terms provided

at https:// standards .iso .org/ iso -iec/ 21838/ -2/ ed -1/ en/ establishes conformity of BFO-2020 to

ISO/IEC 21838-1:—, 4.1.
4.3 OWL 2 formalization of BFO-2020

The OWL 2 formalization of BFO-2020, provided in the file BFO-2020-OWL (https:// standards .iso .org/

iso -iec/ 21838/ -2/ ed -1/ en) establishes conformance to ISO/IEC 21838-1:—, 4.2. BFO-2020-OWL consists

of the following parts:
4.3.1 BFO-2020.owl – OWL in rdf format.
[8]
4.3.2 BFO-2020.ofn – OWL in functional syntax with URIs.

4.3.3 BFO-2020-labelled.ofn – OWL in functional syntax with labels instead of URIs.

4.3.4 BFO-2020-iris.xlsx – table of IRIs for all classes and relations in BFO-2020-CL, including all

classes and relations in BFO-2020-OWL.

4.3.5 bfo-relations-table.xlsx – table showing all relations in BFO-2020 including all inverses and all

binary variants used in BFO-2020-OWL.

4.3.6 temporalized-definitions.cl – the set of CL definitions of binary at-all-times/some-time

relations used in BFO-2020-OWL.

4.3.7 temporalized-definitions.prover9 – the set of definitions of binary at-all-times/some-time

[2]
relations used in OWL (as for 4.3.3) but in prover9 format .
4.4 Common Logic axiomatization of BFO-2020
4.4.1 General

The CL formalization of BFO-2020 (provided at https:// standards .iso .org/ iso -iec/ 21838/ -2/ ed -1/ en) to

ISO/IEC 21838-1:—, 4.3, BFO-2020-CL is provided in the following formats:

a) axiomatization in Common Logic Interchange Format (CLIF) as specified in ISO/IEC 24707 provided

in the common-logic directory;
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b) axiomatization using prolog style variables for ingestion in the prover9 automated theorem prover

is documented in Reference [2] is provided in the prover9 directory;

c) axiomatization in standard first-order predicate logic notation is provided in the pdf directory.

4.4.2 Modularity

The axioms in BFO-2020-CL are divided into the following sections in conformance with the requirement

of explicit modularization at ISO/IEC 21838-1:—, 4.1.
Continuant Mereology Order
Domain and Range Participation
Existence and Instantiation Spatial Region
Generic Dependence Spatiotemporal Region
History Specific Dependency
Material Entity Temporal Region
Occurrent Mereology Universal Declaration
4.5 Specification of the purpose of BFO (in conformance with ISO/IEC 21838-1:—,
4.4.2)
4.5.1 General

BFO is designed as a top-level ontology that can serve as a starting point for definitions in suites of

domain ontologies in conformance with ISO/IEC 21838-1:—, 4.4.2. Examples of such suites using BFO in

this manner are provided in 4.5.2 and 4.5.3.
4.5.2 Example Open Biomedical Ontologies (OBO)
Bacterial Clinical Infectious Diseases Ontology Mental Disease Ontology (MFOMD)
(BCIDO)
Beta Cell Genomics Application Ontology Mental Functioning Ontology (MFO)
(BCGO)
Biological Collections Ontology Ontology for Adverse Events (OAE)
(BCO)
Cell Ontology (CL) Ontology for Biobanking (OBIB)
Cell Line Ontology (CLO) Ontology of Biological and Clinical Statistics
(OBCS)

Chemical Entities of Biological Interest Ontology for Biomedical Investigations (OBI)

(CHEBI)
Common Anatomy Reference Ontology Ontology for General Medical Science (OGMS)
(CARO)
Drug Ontology (DRON) Ontology of Medically Related Social Entities
(OMRSE)
Emotion Ontology (MFOEM) Oral Health and Disease Ontology (OHD)
Environment Ontology (ENVO) Plant Ontology (PO)
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Gene Ontology (GO) Population and Community Ontology (PCO)
Human Disease Ontology (HDO) Protein Ontology (PRO)
Infectious Disease Ontology (IDO) Relations Ontology (RO)
Information Artefact Ontology (IAO) Vaccine Ontology (VO)
[5]

Documentation of these and other OBO Foundry ontologies is provided at http:// obofoundry .org .

4.5.3 Example Common Core Ontologies (CCO)
Agent Ontology Information Entity Ontology
Artefact Ontology Modal Relation Ontology
Currency Unit Ontology Quality Ontology
Event Ontology Time Ontology
Extended Relation Ontology Units of Measure Ontology
Geospatial Ontology
The CCO suite is extended by a series of application ontologies, including:
Aircraft Ontology Mission Planning Ontology
Airforce Aircraft Maintenance Ontology Occupation Ontology
Army Universal Task List Ontology Outer Space Ontology
Airforce Aircraft Maintenance Ontology Physiographic Feature Ontology
Army Universal Task List Ontology Sensor Ontology
Emotion Ontology Skills Ontology
Hydrographic Feature Ontology Space Object Ontology
Legal and Criminal Act Ontology Transportation Infrastructure Ontology
Military Operations Ontology Undersea Warfare Ontology
Mission Planning Ontology Watercraft Ontology

Documentation of these and other common core ontologies is provided in Reference [6].

4.6 Description of how conformance of a domain ontology to BFO is established (in

conformance with ISO/IEC 21838-1:—, 4.4.3)
4.6.1 Overview

Where BFO serves as starting point for the development, or for the re-engineering, of domain ontologies

or other external ontology resources, the conformance of the latter to BFO in conformance with

ISO/IEC 21838-1:—, 4.4.3 is established in the following ways.
4.6.2 Conformance through direct extension

One common strategy used to ensure conformance of a domain ontology to BFO is to load BFO into

an ontology editor and construct the domain ontology ab initio on this basis. Terms in BFO are then

used as starting point for defining the topmost set of domain ontology terms as specializations of the

relevant BFO categories. Categories shall be used for this purpose that are at the lowest level in the BFO

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hierarchy suitable for the purposes of the domain ontology, and in any case at a level below "entity".

Conformance for a domain ontology constructed in this way requires:

a) that the result of adding the domain ontology terms and relational expressions to BFO is a consistent

ontology.
In addition, it requires that each term in the domain ontology is either:
b)1) connected to BFO via some unique chain of is_a relations, or

b)2) able to be defined through some logical combinations of terms satisfying b)1) but not itself such as

to satisfy b)1).
In the latter case, the term refers to a defined class (see definition 3.5).

The requirement of uniqueness in b)1) implies that all terms in the resulting ontology that refer to

universals (in the sense of definition 3.2), rather than to defined classes, form a hierarchy governed by

single inheritance (no term in the resulting ontology shall have more than one parent).

Adding a domain ontology to BFO, in some cases, results in a conservative extension of BFO (thus no

more theorems using only terms and relational expressions in the signature of BFO will be provable

using BFO extended by the domain ontology than are provable using BFO alone). In cases where the

domain ontology relates to universals – for example time and space in a physics ontology – which are

BFO categories, then the result might not be a
...

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