◆ Semantic Web Catalogue

Problem thread

Unknown or false?

When a fact is missing, is it unknown or false, and how do you check data in a world that assumes it is merely unknown?

issue
query & validation
also reasoning
status
largely settled
steps
8, 1978–2026
threads
all problem threads

Databases treat whatever they cannot show to be true as false, which makes it easy to check that a record is complete. OWL makes the opposite assumption, suited to a Web where nobody has all the facts, but it cannot tell you that data is missing. By 2013 practitioners had no standard way to validate RDF; Shape Expressions and then SHACL filled the gap with closed, schema-like checks alongside open-world reasoning.

Lineage

  1. 1978
    proposes writing ★ seminal
    On Closed World Data Bases

    Formalizes the closed-world assumption: what is not known to be true is taken to be false. [src1][src2]

  2. 10 Feb 2004
    proposes concept
    Open-world assumption

    The Semantic Web adopts the opposite rule: descriptions of a resource are not confined to one file or scope, so a fact missing from the data is unknown rather than false. [src]

  3. 10 Feb 2004
    proposes standard ★ seminal
    OWL

    OWL makes an open-world assumption: a fact missing from the data is unknown, not false, so new information can always be added. [src]

  4. 15 Jan 2008
    workaround standard ★ seminal
    SPARQL

    A query matches only the data that is there, so SPARQL queries can check constraints in practice; but such queries are hard for people or machines to inspect and understand. [src1][src2]

  5. 2013
    poses writing
    Report of the W3C RDF Validation Workshop

    Participants agree there is no standard for checking RDF data against constraints. A majority supports a W3C Working Group for a declarative way to express basic integrity constraints. [src]

  6. 4 Sep 2014
    proposes writing
    Shape Expressions: An RDF Validation and Transformation Language

    Shape Expressions: a structural schema language for RDF graphs, for validating, traversing and transforming them. [src1][src2]

  7. 20 Jul 2017
    settles standard ★ seminal
    SHACL

    A W3C language for validating RDF data against shapes, closer to schema checking than to OWL's open-world reasoning. [src]

  8. 17 Sep 2026
    proposes standard
    SHACL 1.2

    SHACL 1.2 adds inference rules that derive new triples from existing ones, bringing a kind of reasoning into the closed-world validation language. [src]

Open now

Under each question, the answers people have put forward or built. The catalogue gives no odds on them.

  • How should shapes validate statements about statements in RDF 1.2? [src]
    The W3C Data Shapes Working Group's mission is to update the shapes standards for the versions of RDF that support RDF-star.
    • SHACL 1.2 builds triple terms and reifiers into shapes. SHACL 1.2
      The SHACL 1.2 drafts adopt RDF 1.2's terminology for triple terms and reifiers.[src]
  • Will ShEx and SHACL stay two languages for the same job? [src1][src2]
    Both describe the shape RDF data should have; SHACL is the W3C Recommendation, while ShEx is maintained by a community group and used for Wikidata's EntitySchemas.
    • Both live on, each where it took root.
      SHACL is the W3C standard; ShEx is maintained by a community group and used for Wikidata's EntitySchemas.[src1][src2]

Decision points

Dated moments when a decision or a deadline can change the outcome.

  1. 31 Dec 2026
    Data Shapes Working Group charter ends charter

    The W3C group writing SHACL 1.2 is chartered until the end of 2026; W3C members decide on an extension or a new charter.[src]

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