ISO/IEC 21838-2:2021

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)

General Information

• Status: Published
• Publication Date: 29-Nov-2021
• ICS: 01.040.35 - Information technology (Vocabularies)
• ICS: 35.060 - Languages used in information technology
• Technical Committee: ISO/IEC JTC 1/SC 32 - Data management and interchange
• Drafting Committee: ISO/IEC JTC 1/SC 32/WG 2 - MetaData
• Current Stage: 6060 - International Standard published
• Start Date: 30-Nov-2021
• Due Date: 30-Jun-2020
• Completion Date: 30-Nov-2021

Overview

ISO/IEC 21838-2:2021 specifies the Basic Formal Ontology (BFO-2020), a domain-neutral top-level ontology (TLO) intended to support semantic interoperability among heterogeneous information systems. BFO provides a small set of highly general categories (e.g., object, quality, process, spatial/temporal region) and formal resources to promote coordinated, non‑redundant development of domain ontologies. The standard documents BFO-2020 in natural language and provides formal axiomatizations in OWL 2 and Common Logic (CL), and it demonstrates conformity to the requirements of ISO/IEC 21838‑1.

Key Topics

• Definitions and relations: Natural‑language definitions for BFO‑2020 terms and relational vocabulary to guide human understanding and maintenance.
• Formal axiomatizations: Machine‑readable versions - BFO-2020-OWL (OWL 2) for tool integration and reasoning, and BFO-2020-CL (Common Logic) for higher expressivity (time, space, parthood).
• Conformance requirements: How BFO meets the top‑level ontology requirements in ISO/IEC 21838‑1, including modularity and conformance validation strategies.
• Domain ontology integration: Specification of requirements for a domain ontology to act as a module when BFO is the top‑level hub (direct and indirect extension, re‑engineering paths).
• Interpretability and consistency: Documentation and strategies for demonstrating CL consistency and OWL↔CL interpretability.
• Scope boundaries: The standard does not attempt to standardize ontology languages, reasoning methods, or translators between ontology notations.

Applications

• Enable semantic interoperability across diverse systems by providing a common, neutral upper ontology.
• Guide ontology engineers and data architects in building BFO‑conformant domain ontologies (life sciences, biomedical ontologies, data/information science, sustainable development, engineering, defense, intelligence).
• Support ontology quality control and automated reasoning via the OWL 2 axiomatization.
• Use the CL axiomatization where richer expressivity is required (complex temporal, spatial, parthood relations).

Who Should Use It

• Ontology developers and maintainers
• Data architects and semantic engineers
• Research groups building domain ontologies (e.g., biomedical, environmental)
• Organizations aiming for cross‑system data integration and long‑term ontology governance

Related Standards

• ISO/IEC 21838‑1:2021 - Part 1: Requirements for top‑level ontologies (normative reference for conformance).
• Other parts of the ISO/IEC 21838 series (for broader TLO governance and related guidance).

Keywords: ISO/IEC 21838-2:2021, Basic Formal Ontology, BFO, top-level ontology, TLO, OWL 2, Common Logic, ontology conformance, interoperability, domain ontology.

Standards Content (Sample)

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 2021
© 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
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Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
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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
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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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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
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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).
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For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
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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.
v
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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.
vi
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Figure 1 — BFO-2020 is_a hierarchy
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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
© ISO/IEC 2021 – All rights reserved

— 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.
© ISO/IEC 2021 – All rights reserved

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;
© ISO/IEC 2021 – All rights reserved

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
© ISO/IEC 2021 – All rights reserved

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 Transpor
...