W3C and related
W3C - WWW
Security and cryptography
- W3C Security Vocabulary (draft) - originated in web payments, 2016, addresses crypto, GraphSignature, LinkedDataSignature
- W3C Web CryptoAPI (for usage under a browser, as an alternative for an applet)
- W3C WebAuthn API for public key-based credentials by web applications
- Defines an API enabling the creation and use of strong, attested, scoped, public key-based credentials by web applications,
for the purpose of strongly authenticating users. Conceptually, one or more public key credentials,
each scoped to a given WebAuthn Relying Party, are created by and bound to authenticators as requested by the web application.
The user agent mediates access to authenticators and their public key credentials in order to preserve user privacy.
Authenticators are responsible for ensuring that no operation is performed without user consent.
Authenticators provide cryptographic proof of their properties to Relying Parties via attestation.
This specification also describes the functional model for WebAuthn conformant authenticators,
including their signature and attestation functionality.
- W3C WebAuthn Wikipedia
Multiple roots (which leads to graphs)
- ES - Rhizomik - tools and research - mapping XML/OWL, Uni of Lleida, Catalunya
Linked data and vocabularies
JSON-LD is a JSON-based format to serialize Linked Data.
JSON-LD is primarily intended to be a way to use Linked Data in Web-based programming environments,
to build interoperable Web services, and to store Linked Data in JSON-based storage engines.
- json-ld.org - json linked data
- W3C json-ld specification that introduces:
- a universal identifier mechanism for JSON objects via the use of IRIs,
- a way to disambiguate keys shared among different JSON documents by mapping them to IRIs via a context,
- a mechanism in which a value in a JSON object may refer to a resource on a different site on the Web,
- the ability to annotate strings with their language,
- a way to associate datatypes with values such as dates and times, and
- a facility to express one or more directed graphs, such as a social network, in a single document.
- W3C json-ld community
- json-ld - Wikipedia
Solid - Tim Berners-Lee and Lalane Kagal
Solid (derived from "social linked data") is a proposed set of conventions and tools for building decentralized social
applications based on Linked Data principles. It relies as much as possible on existing W3C standards and protocols. These are:
- RDF (by default Turtle, otheriwse JSON-LD and RDFa)
- WebID 1.0 (Web Identity and Discovery)
to provide universal usernames/IDs for Solid apps, and to refer to unique Agents (people, organizations, devices).
WebIDs, when accessed, yield WebID Profile documents (in Turtle and other RDF formats).
- FOAF vocabulary is used both in WebID profiles, and in specifying Access Control lists.
- Authentication (for logins, page personalization and more) is done via the WebID-TLS protocol.
WebID-TLS extends WebID Profiles to include references to the subject's public keys in the form of X.509 Certificates,
using Cert Ontology 1.0 vocabulary. The authentication sequence is done using the HTTP over TLS protocol.
- HTML5 keygen. Unlike normal HTTPS use cases, WebID-TLS is done without referring to Certificate Authority hierarchies,
and instead encourages host server-signed (or self-signed) certificates. In Solid, certificate creation is typically done
in the browser using the HTML5 keygen element, to provide a one-step creation and certificate publication user experience.
- Authorization and access lists are done using Basic Access Control ontology
(see also the WebAccessControl wiki page for more details).
- Support for WebID-OIDC as another primary authentication mechanism is on its way.
It is based on the OAuth2/OpenID Connect protocols, adapted for WebID based decentralized use cases.
- The Linked Data Platform (LDP) standard is used for reading and writing generic
Linked Data resources through HTTP operations on web resources.
Solid project and specifications
Solid and W3C
- Inrupt - commercial startup co-founded by CEO John Bruce and CTO Sir Tim Berners-Lee
- Inrupt.net - cloud-hosted instance of the open source software Node Solid Server
- Created primarily to provide open source application developers with Pods to test against
- Products include:
- Inrupt Enterprise Solid Server - A production-grade Solid server produced and supported by Inrupt
- Node Solid Server - An open source server created by MIT
- GLEIF.org established by the Financial Stability Board (FSB), specifies 4 ontologies:
- GLEIF L1 level 1 ontology, Who is Who, covers key reference data for a
legal entity identifiable with an LEI, builds on ISO 17442
- GLEIF L2 level 2 ontology, Who Owns Whom, for legal entity parent relationships.
- Entity Legal Form ontology defining concepts for Entity Legal Forms
and their abbreviations by jurisdiction, based on ISO 20275
- Registration Authority ontology defining concepts for Business Registries,
including the jurisdictions served
- LEI resolver - ref Robert Trypuz, see also ECB Francis Gross
- uses the Financial Industry Business Ontology (FIBO) as an upper-level ontology.
Various aspects of the schemata of the different datasets are mapped to the corresponding FIBO classes and relationships. In this way, one can query across different datasets using FIBO. The following two modules of FIBO have been loaded into FactForge:
- Foundations, version 14-11-30 (November 2014);
- Business Entities, version 15-02-23 (February 2015)
includes more than 1 billion facts from popular datasets such as DBpedia, Geonames, Wordnet, GLEIF, the Panama Papers, etc.,
as well as ontologies such as the Financial Industry Business Ontology (FIBO)
- DBPedia: the structured version of the Wikipedia encyclopedia. Only the English version of DBPedia is loaded.
- Geonames: a worldwide geographical database, which “contains over 10 million geographical names and consists of over 9 million unique features whereof 2.8 million populated places”.
- Wordnet: popular semantic dictionary for English. Words “are grouped into sets of cognitive synonyms (synsets),
each expressing a distinct concept. Synsets are interlinked by means of conceptual-semantic and lexical relations”. It contains 117.000 synsets.
- WorldFacts: dataset about countries, languages, currencies and other related information.
Developed by the DBPedia association and includes information derived from LEXVO, CIA World FactBook and other datasets.
- Linked Leaks: The LOD version of the Panama Papers database released by the International Consortium for Investigative Journalism (ICIJ) in May 2016.
It includes “about 200,000 offshore entities that are part of the Panama Papers investigation and about more than 100,000 additional
companies that were part of the 2013 ICIJ Offshore Leaks investigation”.
- GLEI (Global Legal Entity Identifier): profiles of about 211 000 organizations, derived from the GMEI utility data dump from April 2016. “The Global Markets Entity Identifier (GMEI) utility is DTCC’s legal entity identifier solution offered in collaboration with SWIFT. The GMEI utility is a pre-Local Operating Unit of the Global Legal Entity Identifier System (GLEIS)”
- NOW News: article texts and metadata for a stream of general news. The metadata includes annotations that link mentions of entities (e.g., people or organizations) and concepts (e.g., “chocolate” or “recession”) in the news to the corresponding DBPedia and Wikidata concepts.
- UNBIS - United Nations Thesaurus
- ISO OBP - ISO's Online Browsing Platform - preview before you buy
- IEC IEV - IEC's online terminology database of electrotechnical vocabulary
EC ISA, PO, SEMIC and related
- Digit ISA2 core vocabularies
- Core Person: captures the fundamental characteristics of a person, e.g. name, gender, date of birth, location, and is referenced at by W3C for person
- Registered Organisation: captures the fundamental characteristics of a legal entity (e.g. its identifier, activities) which is created through a formal registration process, typically in a national or regional register
- Core Location: captures the fundamental characteristics of a location, represented as an address, a geographic name or geometry
- Core Public Service: captures the fundamental characteristics of a service offered by a public administration
- Core Criterion and Core Evidence: describe the principles and the means that a private entity must fulfil to become eligible or qualified to perform public services. A Criterion is a rule or a principle that is used to judge, evaluate or test something. An Evidence is a means to prove a Criterion
- Core Public Organisation: describes public organisations in the European Union
- Core Public Event Vocabulary: under development
- Semantic Interoperability Community (SEMIC) page on core vocabularies
Publications Office (PO)
PwC's ELI test project
- EU Publications Office (PO)- uses controlled vocabularies, ontologies, models, ...
- EU PO EuroVoc - Multilingual, multidisciplinary thesaurus covering the activities of the EU, the European Parliament in particular. It contains terms in 23 official EU languages, plus in three languages of countries which are candidates for EU accession.
- EU PO Metadata specifying how to describe legal information, the PO's Meta Data Register (MDR) provides access to a number of value lists relevant to ELI implementation, including the Named Authority Lists (NAL)
- CELLAR stores all PO's content and metadata, and the major portals (EUR-Lex, OP Portal), its resources are semantically described
by the CDM (Common Data Model), an FRBR-compliant OWL ontology, serving as the basis for ELI. A public SPARQL endpoint is available
- EUR-LEX ELI- the European Legislation Identifier to make legislation available online, specifying:
- web identifiers (URIs) for legal information
- a specific language for exchanging legislation in machine-readable formats
Started by Mark Musen 1987, much work done by Natasha Noy.
- Stanford's Protégé - desktop and web versions (webversion does not support reasoning)
- Protégé Github
- Protégé basics at wiki.opensemanticframework.org
- Desktop Protégé 5.0.0
- WebProtégé - userid required
- Careful: By uploading, emailing, posting, publishing or otherwise transmitting content to any Forum or submitting any content to WebProtégé, you automatically grant (or warrant that the owner of such rights has expressly granted) WebProtégé a perpetual, royalty-free, irrevocable, nonexclusive right and license to use, reproduce, modify, adapt, publish, transmit and distribute such content on in any form, medium, or technology now known or later developed.
In addition, you warrant that all so-called moral rights in the content have been waived.
- Protégé Wiki
- Protégé Wiki ontology library
- Introduction to OWL reasoning
- OntoDebug - plugin
- Protégé Wiki- SWRL
- SWRL plugin for Protégé 5
- OWLViz for Protégé 5 - OWL visualisation
- VOWL plugin for Protégé 5 - OWL visualisation
- RDF4J- RDF Java framework plus native in-memory and on-disk repositories
- RDF4J docs
- RDF4J API doc
- open source Java framework for processing RDF data
- includes parsing, storing, inferencing and querying of/over such data
- allows to connect with SPARQL endpoints such its own native repositories, Ontotext, Stardog, Virtuoso etc
- BG - Ontotext's GraphDB - originally called OWLIM (OWL in Memory), but when a transactional, index-based file storage layer was added, the name was no longer appropriate
- Packaged as a Storage And Inference Layer (SAIL) for RDF4J
- GraphDB as used in FactForge - open Data and News about People, Organizations and Locations, sample SPARQL queries
- GraphDB quick-start
- KIM for semantic annotation - now integrated in the platform
- tag.ontotext.com - tagging service, semantically enrich your content with annotations such as Person, Organization, Location, and the relationships between them;
- Apache Jena Fuseki SPARQL server
- US - TopQuadrant's TopBraidComposer
- US - OpenLinkSw's Virtuoso
- Metaphacts demo on Cultural Heritage - British Museum
- Amazon Neptune
- Cultural Heritage CIDOC CRM (Conceptual Reference Model)- provides definitions and a formal structure for describing the implicit and explicit concepts and relationships used in cultural heritage, ISO 21127:2006
- AT - SWC's PoolParty - (e.g. Wolters-Kluwer)
- OracleDB supports semantic features
- US - SemanticArts - Michael Ushold
- BE - Ontoforce - biomedical
- RomanticWeb - Relational Object Model for Semantic Web in .net
- US - Stardog - supports the RDF graph data model; SPARQL query language; property graph model and Gremlin graph traversal language; OWL 2 and user-defined rules for inference and data analytics; virtual graphs; geospatial query answering; and programmatic interaction via several languages and network interfaces.
- AT - Semantic Web Company
- FI - Leiki
- Semafora - ontology modelling and inferencing (ontobroker - ex Karlsruhe Institute of Technology)
Architecture and blockchain
Architecture - REST - Web Services
Blockchain and Ontology
Semantics - initiatives
- LinkedData.org - a home for, or pointers to, resources from across the Linked Data community
Wikipedia and friends
- Wikimedia is a global movement to bring free educational content to the world
- DBpedia is a crowd-sourced community effort to extract structured content from the information created in various Wikimedia projects
- Is an ongoing project at infai.org in Leipzig
- DBpedia Slack login with Google
- DBpedia ontology
- Ontology classes
- The DBpedia Ontology is a shallow, cross-domain ontology, which has been manually created based on the most commonly used infoboxes within Wikipedia
- The ontology currently (2018-10) covers 685 classes which form a subsumption hierarchy and are described by 2,795 different properties
- DBpedia 3.2 used an infobox extraction method based on hand-generated mappings of Wikipedia infoboxes to the DBpedia ontology, where
the mappings defined rules on how to parse infobox values
- DBpedia 3.5 introduced a public wiki for writing infobox mappings, allowing external contributors to define mappings for the infoboxes
they are interested in and to extend the existing DBpedia ontology with additional classes and properties
- DBpedia 3.7 uses a directed-acyclic graph (not a tree) as ontology, so classes may have multiple superclasses, which was important for the mappings to schema.org.
A taxonomy can still be constructed by ignoring all superclasses except the one that is specified first in the list and is considered the most important.
- DBpedia SPARQL endpoint
- DBpedia extraction frameworktto extract different kinds of structured information from Wikipedia, it is written using Scala 2.8
- DBpedia Spotlight performs named entity extraction, including entity detection and name resolution, can also be used for named entity recognition
Applications - general
Applications - vendors
Applications - music
- Musicbrainz.org - database and tagging service used by a.o. Amarok
- dbtune.org - hosts a number of servers, providing access to music-related structured data, in a Linked Data fashion
- Jamendo.com- a community collection of music all freely licensed under Creative Commons licenses
Applications - trust
Semantics - RDF - Turtle - SPARQL - OWL - SKOS - DC
Interesting: cryptographic definition of semantic security:
In cryptography, a semantically secure cryptosystem is one where only negligible information about the plaintext can be
feasibly extracted from the ciphertext. Specifically, any probabilistic, polynomial-time algorithm (PPTA) that is given the
ciphertext of a certain message m (taken from any distribution of messages), and the message's length, cannot determine
any partial information on the message with probability non-negligibly higher than all other PPTA's that only have access
to the message length (and not the ciphertext).
This concept is the computational complexity analogue to Shannon's concept of perfect secrecy.
Perfect secrecy means that the ciphertext reveals no information at all about the plaintext,
whereas semantic security implies that any information revealed cannot be feasibly extracted.
Semantic Web - basics
Semantics - Turtle and RDF
Semantics - SKOS - 2009 - W3C
The Simple Knowledge Organization System (SKOS) is an RDF vocabulary for representing semi-formal knowledge organization systems (KOSs),
such as thesauri, taxonomies, classification schemes and subject heading lists. SKOS is based on RDF. In SKOS, conceptual resources (concepts)
can be identified with URIs, semantically related through hierarchies and association networks, labeled with lexical strings,
documented with notes, and aggregated into concept schemes.
SKOS can be used on its own, or in combination with more-formal languages such as OWL. SKOS can be seen as a bridging technology, providing
the missing link between the rigorous logical formalism of OWL and the informal and weakly-structured world of Web-based collaboration
tools, as exemplified by social tagging applications.
The aim of SKOS is not to replace original conceptual vocabularies in their initial context of use,
but to allow them to be ported to a shared space, based on a simplified model, enabling wider re-use and better interoperability.
Semantics - DAML - superceded by OWL
Semantics - SPARQL - SPIN - SHACL
SPARQL - a recursive acronym for SPARQL Protocol and RDF Query Language.
SPIN - SPARQL Inferencing Notation
SHACL - Shapes Constraint Language
- SPINrdf.org - the initial informal SPIN working group and the earliest versions of the SPIN specification
- W3C SPIN submission - 2011 (overview, syntax, modeling vocabulary)
Apparently SPIN did not (yet) make it to a W3C recommendation but rather was succeeded by SHACL
- SPIN - Overview and Motivation
- SPIN - SPARQL Syntax
- SPIN - Modeling Vocabulary
Semantics - W3C OWL
- W3.org - Ontologies and vocabularies
- W3C OWLED community
- W3.org - OWL and OWL 2 standards
OWL is a computational and declarative logic-based language so that knowledge expressed in it can be reasoned with to verify the consistency of the knowledge or how to make implicit knowledge explicit
- OWL uses the open world assumption (OWA - if a fact is missing it may still be true, but simply missing), as opposed to the closed world assumption (if fact is not present in DB it is assumed to be false)
- An OWL ontology maps to DL knowledge base, Tbox, RBox and Abox
- Three species of OWL:
- OWL Full, the union of OWL syntax and RDF
- OWL DL, restricted to a decidable FOL fragment (corresponds to DAML+OIL)
- OWL Lite, an easier to implement subset of OWL DL
- Can be specified in five syntaxes:
- W3.org - TR OWL Guide - 2004
- W3.org - TR OWL 2 overview - 2009
- W3.org - TR OWL 2 primer - 2012
- W3.org - OWL DL Query - Manchester Syntax (as used in Protégé)
- OWL Design Patterns - Public Catalog - e.g. N-ary Relations, Closure, ValuePartition, ValueSet,...
- University of Manchester - OWL group
Semantics - SHACL
Ontologies and Vocabularies
Ontologies and Vocabularies - W3C - general
Ontologies and Vocabularies - W3C - CA and Provenance
- W3C CertOnto - Certification Authority ontology - certificate/public key/private key/...
- W3C Provenance- overview of documents - 4 recommendations
- Provenance Wiki at Semantic Web
- Provenance Wiki (by initial working group, now closed)
- Provenance FAQ
- Provenance Implementations
- Provenance components including
- Provenance examples of the various ontology components
- Provenance examples second and more recent list
- Luc Moreau homepage
- The Provenance Book by Luc Moreau and Paul Groth
- Luc Moreau Provtoolbox is a Java library to create Java representations of PROV-DM, and convert them between RDF, PROV-XML, PROV-N, and PROV-JSON
- Open Provenance (based on Luc Moreau) including toolbox with Java, Python, Prov-N editor etc
- Open Provenance Store for storing provenance documents
- SOTON Provenance tools
- ProvoViz tool - visualisation of provenance graph expressed PROV-O vocabulary as an Sankey diagram (upload turtle or rdf/xml
- TheGazette - UK's official public record, The Gazette is published by TSO (The Stationery Office) under the superintendence of Her Majesty's Stationery Office (HMSO), part of The National Archives, content available under the Open Government Licence v3.0
- TheGazette using provenance and digital signature
- TheGazette provenance described by Luc Moreau
- BBC on using the Provenance ontology
- REPRODUCE-ME ontology - for reproduction of experiments, based on PROVO and P-PLAN, by Sheeba Samuel
- REPRODUCE-ME ontology - github Sheeba Samuel (onto, sparql queries etc)
Ontologies and Vocabularies - well-known
- dublincore.org - a vocabulary of fifteen properties for use in resource description as metadata terms - also ISO 15836
- the classic 15 metadata terms are referred to as the Dublin Core Metadata Element Set (DC MES)
- DC MES got integrated into the DCMI Metadata Terms, which are regularly updated
OMG and related
- OMG SBVR - Semantics Of Business Vocabulary And Rules
- SBVR is aligned with Common Logic – published by ISO as ISO/IEC 24707:2007
- FIBO - Financial Industry Business Ontology
- A joint effort by OMG and the Enterprise Data Management (EDM) Council
- See also EDMC github FIBO
- FIBO Foundations, FIBO Business Entities and FIBO Indices and Indicators
- Specification Documents
- Normative Documents
- Normative Machine Readable Documents, a series of RDF/XML files
- Informative Machine Readable Documents
- Foundations address people, agents, currency, agreements, contracts, dates, goals, objectives, ...
- FIBO - Foundations version 1.1
- FIBO - Foundations version 1.2
- Business Entities address corporations, government entities, functional entities, ...
- FIBO - Business Entities version 1.1
- FIBO - Business Entities version 1.0
- FIRO - Financial Industry Regulatory Ontology,
a series of interlinked Ontologies based on industry standards to capture regulatory imperatives and rules in formal semantics.
- Developed by the Governance, Risk and Compliance Technology Centre (Ireland), Tom Butler
- It also expresses the abstract model followed by the other GRCTC projects:
the parser (Hermes), the Methodology (RIM), the XML Schema (Mercury), the Tool (Ganesha), FiORO
- Firo conists of
- FIRO-H(ighLevel)- a core legal ontology about regulatory compliance, centred around the concept of Requirement
(Rule Statement) and the concept of Action, and defined in OWL.
- FIRO-Structure (FIRO-S) deals with the structure and the semantics of the source document.
It accounts for legal and non-legal documents alike.
The purpose of FIRO-S is to integrate information from the source text part of Mercury to allow querying,
Regulatory Change Management, and reasoning.
FIRO-S relies on LegalDocML for the representation of the structure and the semantics of the legal document.
FIRO-S is not formalized in OWL.
- FIRO-Domain (FIRO-D) identifies the domain ontologies based on FIRO-H.
Each contains one rulebook and the related vocabulary.
This means that different rulebooks result in different instances of FIRO-Domain, and any common rule (or vocabulary entry)
will be present in all relevant instances. Its possible applications include:
- Extract the rules valid for a particular point in time (exploiting RCM of FIRO-S).
- Classify instances of RegulatoryStatements as exceptions to other RegulatoryStatements.
- Classify BusinessRules as ensuring compliance with LegalRules.
- FIRO-PurposeSpecific (FIRO-PS) is the ontology used for performing reasoning towards a specific application.
It is a specialization of one or more FIRO-Ds. It may contain Factor instances to represent (either real or fictional) data.
Its possible applications include:
Classify Events (instances of Actions) on the basis of their relation to RegulatoryStatements, as either “relevant”, “complying”, “allowed”, “breaching”, “exempted”.
- FinRegOnt - Financial Regulation Ontology - based on LKIF and FIBO
- CEN Metalex ontology
- Usage of the CEN Metalex ontology
- OASIS LegaldocML - Akoma Ntoso
- The LegalDocumentXML Specifications provide a common legal document standard for the specification of parliamentary,
legislative, and judicial documents, for their interchange between institutions anywhere in the world, and for the creation
of a common data and metadata model that allows experience, expertise, and tools to be shared and extended by all
participating peers, courts, Parliaments, Assemblies, Congresses, and administrative branches of governments.
The standard aims to provide a format for long-term storage of and access to parliamentary, legislative and judicial
documents that allows search, interpretation, and visualization of documents.
- OASIS LegalruleML
- The objective of the LegalRuleML TC is to extend RuleML with formal features specific to legal norms, guidelines,
policies and reasoning; that is, the TC defines a standard (expressed with XML-schema and Relax NG) that is able to represent
the particularities of the legal normative rules with a rich, articulated, and meaningful markup language.
- OASIS LegalXML enotary with use cases
- OASIS LegalXML courtfiling
- OASIS LegalXML econtracts
- EU Publications - Metadata Registry for e.g. OJ
- EDM Council (EDMC) - FIBO (ref FIBO github), Knowledge Graphs, DCAM, ...
- Schema.org- helping the search engine - a collaborative, community activity to create, maintain, and promote schemas for structured data on the Internet. In 2017 its core vocabulary currently consists of 597 Types, 867 Properties, and 114 Enumeration values.
- Working Ontologist - book with examples
- gist - SemanticArts - free and with tutorials
- gist iri for the person class
- US Cyc - AI company with large ontology
- PL - onto.kul.pl - ontology lab Lublin university - Robert Trypuz - Pawel Garbacz
- PL - Robert TrypuzLEI and Unece meat ontos
- OpenLinkSw LinkedIn schema - attempt to describe the proprietary LinkedIn ontology
- InPhO - Indiana Philosophy Ontology project - includes automatic ontology construction
- WOT ontology (Web Of Trust) to facilitate the use of PGP
- ASSERT4SOA - ontology for security certificates
- DOAP ontology (Description Of A Project)
- Martin Hepp
- GoodRelations ontology from Martin Hepp, popular in e-commerce, included in schema.org since 2012
- GoodRelations wiki at W3C
- Product Types Ontology: High-precision identifiers for product types based on Wikipedia
- UNESCO ISCED and ISCED-F - International Standard Classification of Education for organising education programmes and related qualifications by levels and fields
- ISCED 2011 (levels and fields of education) has been implemented in all EU data collections since 2014
- ISCED-F 2013 (fields of education and training) has been implemented since 2016
- Eurostat - uses ISCED and ISCED-F
- EQF- European Qualifications Framework
- SDMX - ISO 17369:2013 describes statistical data and metadata, based on XML, has its own validation and transformation language, and has 3 key components:
- Information model (data and metadata)
- Content-Oriented Guidelines for communication
- IT architecture and tools
Indices content available with semantic metadata
- MakoLab - web analytics - using schema.org to improve search results
Ontology design patterns
- ODP overview
- it is not enough to say that carnivore eats some meat,
as that is equivalent to saying that it can eat another things apart of meat
- a universal restriction that it only eats meat is also needed (the existential and the universal restriction
need to have the same filler)
- Value Partition (at class level) - referred to as enumeration, if it is built using individuals instead of classes.
- a person can be defined as being short, medium or tall, and the attribute height can just get those values
- height is said to be covered or exhausted by those values; the possible heights are only those three
- refer also W3 Tech Report
Logic, Rules and Reasoners