Known Values: A Compact, Deterministic Representation for Ontological Concepts

February 3, 2026 · View on GitHub

BCR-2023-002

Authors: Wolf McNally, Christopher Allen
Date: Aug 15, 2022
Revised: April 26, 2025

This document introduces a standardized namespace of 64-bit unsigned integers that represent ontological concepts, potentially across many vocabularies. This standardization aims to enable compact binary representation, interoperability across systems that exchange semantic information, and enhanced security by mitigating the risks associated with URI manipulation.

Introduction

Ontological concepts are things like relationships between entities (containedIn, spouseOf), classes of entities (human, book), properties of entities (alphaChannel, publicationYear), or enumerated values of properties (female, red). These concepts are used to define the structure and semantics of a domain, describing the types of things that exist and the ways they relate to each other.

Ontological concepts like relationships, classes, and properties stand alone in that they are independent and self-contained entities within the ontology. This is in contrast to something like CBOR tags, which are used to label and interpret specific data values within a particular encoding. CBOR tags depend on the context of the data they are applied to and don't have independent meaning outside that context. Ontological concepts, on the other hand, represent general ideas and relationships that are not tied to specific data values or encodings, giving them a more standalone nature.

In the context of current ontological vocabularies like RDF and OWL the use of URIs to represent concepts, while flexible, introduces possibilities for manipulation and ambiguity in representation. URIs are also verbose and do not lend themselves well to long documents involving many concepts and processing in constrained environments.

The Known Value approach addresses this by associating a unique 64-bit integer with each ontological concept. These integers, referred to as Known Values, are associated with canonical names and synonymous URIs within a centralized registry, ensuring that specific semantics have exactly one valid binary representation.

This approach carries several benefits:

Simplification and Efficiency: Converting ontological concepts into unique integers enables compact encoding in various documents, particularly binary formats like CBOR.
Enhanced Security: Utilizing integers instead of URIs eliminates the surface for manipulation attacks and helps ensure deterministic encoding.

Independence from Gordian Envelope

Known Values are a registry of integer code points representing ontological concepts, usable by anyone for any purpose. While this document defines a CBOR serialization (#6.40000) and Gordian Envelope incorporates Known Values as an extension (see BCR-2023-003), this specification has no normative dependency on either CBOR or Envelope. The registry of codepoint-to-concept mappings stands on its own and may be used in any encoding, protocol, or data format.

Scope

The scope of this specification includes the definition of the Known Value namespace, the structure of the registry, the rules for assigning and managing Known Values.

Appendix A is a list of currently assigned Known Values.

Terminology

Known Value: A unique 64-bit unsigned integer assigned to an ontological concept.
Codepoint: The specific integer representing a Known Value.
Canonical Name: The unique name for the ontological concept.
Registry: A centralized table or database containing the mapping between codepoints, canonical names, and synonymous URIs.

This document assumes familiarity with ontological systems, including RDF, RDFS, OWL, and related standards.

Representation

A Known Value is an unsigned integer in the range 0..2⁶⁴ - 1. When the context is understood it may be encoded in any suitable format.

When a Known Value's name is printed in text, whether as a name or integer value it is surrounded by single quotes (U+0027). For example, the Known Value for isA is printed as either '1' or 'isA'. Therefore the presence of single quotes always indicates a Known Value.

✅ NOTE: The known value 0 (zero) is the "unit type", and is printed as '' (empty string). See BCR-2026-001 for more information.

When serialized as a tagged CBOR structure it uses tag #6.40000. The formal language used is the Concise Data Definition Language (CDDL) [RFC8610].

known-value = uint

tagged-known-value = #6.40000(known-value)

So the tagged-known-value for isA in CBOR diagnostic notation would be:

40000(1)

Since CBOR encodes integers using variable length encoding, the actual bytes encoded would be:

d99c4001

Registry Structure

The Known Value Registry is a centralized database designed to hold the mapping between the unique 64-bit integers (codepoints), canonical names, and synonymous URIs for ontological concepts. This section details the structure and key components of the registry.

Data Structure

Work in progress.

The registry consists of rows, with each row containing the following fields:

Codepoint: A unique 64-bit unsigned integer assigned to an ontological concept.
Canonical Name: The standardized name for the ontological concept.
Type: The type of ontological concept, e.g. class, property, relationship, etc. By convention, classes and enumerated values are CapitalizedCamelCase, while properties and relationships are uncapitalizedCamelCase.
Description: A human-readable description of the concept.
URI: A URI that defines the concept. This may be a URI for an existing ontology, or a URI that is specific to another specification.

Access Controls

Work in progress.

The Known Value Registry shall be maintained with specific access controls to ensure integrity and reliability:

Read Access: Publicly available for any system or user to query and utilize Known Values.
Write Access: Restricted to authorized entities who can propose, modify, or delete entries. The process for becoming an authorized entity is described in section 2.

Consistency and Validation

Work in progress.

The Known Value Registry must maintain consistency and prevent conflicts. Specific validation rules include:

No duplicate codepoints.
No duplicate canonical names.
Validation of URIs to ensure they are valid and conform to the respective ontology standards.

Versioning and History

Work in progress.

The registry should include versioning and maintain a history of changes to allow tracking of modifications, additions, and deletions. This enables traceability and can support rollback in case of erroneous changes.

Assignment Process

Work in progress.

Process for requesting, assigning, and managing Known Values.
Guidelines for what constitutes a valid ontological concept for inclusion.
Considerations regarding similar, duplicate, or conflicting entries.

Interoperability with Existing Systems

Work in progress.

Explanation of how Known Values can be integrated with existing ontological systems like RDF, RDFS, and OWL.
Examples or use cases demonstrating integration with Gordian Envelope, dCBOR, etc.

Security Considerations

Work in progress.

Detailed discussion of the security enhancements achieved through Known Values, including examples.
Any potential security risks or considerations that should be addressed.

IANA Considerations

This document requests the assignment of CBOR tag #6.40000:

Tag	Data Item	Semantics
40000	uint	Known Value

Implementations

The known-values library provides a Rust registry of Known Values, including the ability to encode and decode them in CBOR.

Appendix A: Registry

When encoded as CBOR, the amount of storage required for integer values varies, so ideally more commonly used Known Values would be assigned codepoints requiring less storage.

Range	Bytes
0..23	1+0 = 1
24..255	1+1 = 2
256..65535	1+2 = 3
65536..4294967295	1+4 = 5
4294967296..18446744073709551615	1+8 = 9

Assigned Code Point Ranges

The following table summarizes the assigned Known Value code point ranges:

Name	Range	Entries	JSON
Blockchain Commons	0-999	see registry	JSON
Community Assigned (specification required)	1000-1999	see registry	JSON
RDF	2000-2049	21	JSON
RDFS	2050-2099	15	JSON
OWL 2	2100-2199	75	JSON
Dublin Core Elements	2200-2299	15	JSON
Dublin Core Terms	2300-2499	89	JSON
NISO CRediT	2400-2413	14	JSON
FOAF	2500-2699	75	JSON
SKOS	2700-2799	32	JSON
Solid	2800-2899	33	JSON
W3C Verifiable Credentials	2900-2999	28	JSON
GS1 Web Vocabulary	3000-3999	609	JSON
Schema.org	10000-19999	2450	JSON
Community Assigned (first come-first served)	100000-...	see registry	JSON

Blockchain Commons Core Concepts

The Blockchain Commons range (0-999) contains core concepts used across Blockchain Commons specifications, including but not limited to Gordian Envelope. Where these concepts have equivalent URIs in other ontologies, the external ontology registries reference the Blockchain Commons code point rather than assigning a new one, ensuring 1:1 correspondence between code points and URIs.

Core envelope predicates (0-49): Fundamental properties like isA, id, signed, note, hasRecipient, salt, date, version
Attachments (50-59): Vendor-defined envelope extensions
XID Documents (60-99): Extensible identifier documents for decentralized identity, including privileges like allow, deny, delegate, and operational/management capabilities
Expressions and Functions (100-199): Request/response patterns including result, error, sender, and continuations
Cryptography (200-299): Cryptographic primitives like Seed, PrivateKey, PublicKey, MasterKey
Cryptocurrency (300-499): Asset types (Bitcoin, Ethereum, Tezos) and networks (MainNet, TestNet)
Bitcoin (500-599): BIP-32 HD keys, derivation paths, PSBTs, and output descriptors
Graphs (600-799): Graph structures including directed graphs, DAGs, trees, forests, hypergraphs, and related edge/node predicates

Standard Supported Ontologies

This section describes the ontologies from which Known Values are assigned, organized from most fundamental to most specialized.

RDF (Resource Description Framework)

RDF is the foundational data model of the Semantic Web, providing a standard way to make statements about resources using subject-predicate-object triples. It defines core concepts like rdf:type, rdf:Property, rdf:List, and rdf:Statement. RDF is the most fundamental building block for any semantic system.

RDFS (RDF Schema)

RDFS extends RDF with basic schema vocabulary for defining classes and properties. It provides concepts like rdfs:Class, rdfs:subClassOf, rdfs:domain, rdfs:range, and rdfs:comment. Nearly all other semantic vocabularies are built upon RDF/RDFS primitives.

OWL 2 (Web Ontology Language)

OWL 2 extends RDF/RDFS with more expressive constructs for describing complex relationships and constraints. It provides vocabulary for cardinality restrictions, property characteristics (transitive, symmetric, functional), class expressions (unions, intersections, complements), and reasoning capabilities. OWL enables more sophisticated ontological modeling and automated inference.

Dublin Core (Elements and Terms)

Dublin Core is a widely-adopted metadata vocabulary originally developed for describing digital resources like documents, images, and web pages. The 15 core elements (title, creator, subject, description, publisher, date, etc.) provide a lingua franca for resource metadata. Dublin Core Terms extends this with additional properties and refined semantics. Many other vocabularies reference Dublin Core for basic metadata needs.

NISO CRediT (Contributor Roles Taxonomy)

NISO CRediT is a taxonomy for describing the specific contributions of individuals to scholarly research outputs. It defines 14 distinct contributor roles such as Conceptualization, DataCuration, FormalAnalysis, FundingAcquisition, and WritingReviewEditing. CRediT enables clearer, more transparent attribution of credit across research products and their associated metadata.

SKOS (Simple Knowledge Organization System)

SKOS provides vocabulary for representing knowledge organization systems such as thesauri, classification schemes, taxonomies, and folksonomies. It defines concepts like Concept, ConceptScheme, broader, narrower, prefLabel, and altLabel. SKOS is essential for organizing and relating concepts in controlled vocabularies.

FOAF (Friend of a Friend)

FOAF is a vocabulary for describing people, their activities, and their relationships to other people and objects. It defines classes like Person, Organization, and Document, along with properties like name, knows, mbox, and homepage. FOAF is widely used in social web applications and decentralized identity systems.

Solid

Solid (Social Linked Data) is a W3C project for decentralized data storage and identity. The Solid Terms vocabulary defines concepts for personal data pods, access control, type indexes, and WebID-based authentication. It includes properties like owner, publicTypeIndex, and oidcIssuer that are essential for Solid-based applications.

W3C Verifiable Credentials

The W3C Verifiable Credentials vocabulary provides terms for expressing credentials on the Web in a cryptographically secure, privacy-respecting, and machine-verifiable way. It defines concepts like VerifiableCredential, VerifiablePresentation, credentialSubject, issuer, and proof. This vocabulary is fundamental to decentralized identity and digital credential ecosystems.

GS1 Web Vocabulary

The GS1 Web Vocabulary is an OWL ontology for global supply chain and product identification, published by GS1 (the organization behind barcodes and GTINs). It extends Schema.org with detailed product, organization, and supply chain concepts covering food/beverage/tobacco products, wearable products, allergen details, nutrition information, packaging, certifications, and extensive code lists for regulated product data. The vocabulary defines classes like gs1:Product, gs1:Organization, and gs1:FoodBeverageTobaccoProduct, along with properties for GTINs, ingredient sequences, allergen declarations, and GS1 Digital Link resolver types.

Schema.org

Schema.org is a collaborative vocabulary created by major search engines (Google, Microsoft, Yahoo, Yandex) for structured data on web pages. It provides an extensive vocabulary of over 2,600 types and properties covering diverse domains: creative works, events, organizations, people, places, products, reviews, and more. While less formal than OWL ontologies, Schema.org is the most widely deployed structured data vocabulary on the Web.

Community Known Values

The Known Value namespace reserves code points 100,000 and above for community-submitted registrations. This allows organizations and individuals to register their own ontological concepts while maintaining the centralized coordination benefits of the Known Value system.

The community registration process is automated through GitHub Actions workflows. Submitters create a JSON request file specifying their desired code points (≥ 100,000) and submit it via pull request. The system validates the request for schema conformance, code point availability, and uniqueness constraints. Upon successful validation and merge, the code points are automatically registered in the community registry.

For detailed information on submitting community Known Value requests, including the JSON schema, validation rules, and submission process, see community-known-values/README.md.