RDF Working Group Charter

Background

The Resource Description Framework (RDF), the first layer of the Semantic Web, became a W3C Recommendation in 1999. A major revision was published in 2004, including the general concepts, its semantics, and an XML Serialization (RDF/XML) syntax.

Since then, several newer standards based on RDF have been published, including SPARQL, OWL 2, POWDER, SKOS, and RIF. Through this standardization work, the thriving R&D activities in the area, and an ongoing deployment of these technologies across multiple industries, a number of issues regarding RDF came to the fore. In June 2010 the W3C held a workshop to gather feedback and begin to determine if another revision of RDF is warranted and, if so, which elements should be added or clarified. The workshop established a list of possible work items which was summarized by the report of the workshop. This was followed by a public discussion on various email lists and fora as well as a public questionnaire set up by W3C and which was answered by 126 people from the community. The current charter reflects a consensus reached through those discussions and responses.

Scope

Compatibility and Deployment Expectation

For all new features, backwards compatibility with the current version of RDF is of great importance. This means that all efforts should be made so that

• any valid RDF graphs (in terms of the RDF 2004 version) should remain valid in terms of a new version of RDF; and
• any RDF or RDFS entailment drawn on RDF graphs using the 2004 semantics should be valid entailment in terms of a new version of RDF and RDFS

Care should be taken to not jeopardize exisiting RDF deployment efforts and adoption. In case of doubt, the guideline should be not to include a feature in the set of additions if doing so might raise backward compatibility issues.

New Features and Changes

This charter provides two lists of features: “Required features” and “Time-permitting features”. The former includes features whose inclusion in the final recommendations is required for the Working Group to successfully complete its charter, whereas the latter includes features that the Working Group should consider adding to the final recommendation, but which may be abandoned if the Working Group has insufficient time or resources, or the features would violate the backward compatbility or deployment concerns. The Working Group is expected to give priority in allocating resources to the required features until they are completed.

Beyond the explicit features listed below, the Working Group will also look at the official RDF Errata document and all formally recorded error reports, and introduce changes as appropriate.

Syntax

Required features

• Standardize the Turtle RDF Syntax (see the Workshop result page for further references). Either that syntax or a related syntax should also support multiple graphs and graph stores (see work item listed below). This work should take into account the 14 January 2008 Turtle Syntax document, N3, TriG, and the SPARQL Query Language syntax.
• Define and standardize a JSON Syntax for RDF (see the Workshop result page for further references). The goal is to provide an RDF serialization as complete as possible (including to multiple graphs and graph stores, see work item listed below), but features may be ignored and special syntax features may be introduced if that would greatly facilitate the adoption of the JSON encoding by the Web Application developers’ community.

Time permitting features

• Standardize additions to RDF/XML to address some or all of the features of the Turtle and JSON syntaxes not currently expressable directly in RDF/XML, in a way which degrades gracefully in existing RDF/XML systems. Candidates include multiple graphs and graph stores (see work item listed below) or lists.
• Standardize a subset of RDF/XML suitable for processing with standard XML tools like XSLT and XQuery (e.g., no typed nodes, no nesting, etc).

Support for Multiple Graphs and Graph Stores

The RDF Community has used the term “named graphs” for a number of years in various settings, but this term is ambiguous, and often refers to what could rather be referred as quoted graphs, graph literals, URIs for graphs, knowledge bases, graph stores, etc. The term “Support for Multiple Graphs and Graph Stores” is used as a neutral term in this charter; this term is not and should not be considered as definitive. The Working Group will have to define the right term(s).

Required features

• Standardize a model and semantics for multiple graphs and graphs stores (see the Workshop result page for further references)

Changes/modification to the RDF concepts, model, or semantics

Required features

• Clarify the usage of IRI references for RDF resources, e.g., per SPARQL Query §1.2.4.
• Complete the inference rules that are currently incomplete, and update the entailment lemma (see Herman ter Horst’s paper for further details)
• Deprecate some RDF features (e.g., reification, containers). “Deprecation” in this context means that new deployments, such as data publishers, are advised against using the feature. Conformant systems (parsers, etc) will still be required to implement the feature, i.e., the feature is not removed from the specification, nor is there a commitment that a future release of RDF would remove it.
• Consider reconciling the core RDF(S) documents with semantic features and extensions defined by other W3C Recommendations since 2004 (for example rdf plain literals, the finite versions of the RDF and RDFS entailment regimes defined by SPARQL1.1, or the POWDER-S IRI Set Semantics). The goal is not to redefine those extensions and features, but rather to combine them into one or more, easily referencable document(s).

Time Permitting features

• Harmonize the usage of different data types (or the lack thereof) for plain literals (i.e., XSD’s string and plain literal). The goal is to simplify, e.g., SPARQL queries that, at the moment, require to make three different queries for essentially identical purposes.

Miscellaneous

Required features

• Update and extend the RDF Primer. New features may include multi-syntax examples, more up-to-date in terms of the vocabularies used, may deal with issues around Linked Data like the use of “owl:sameAs”, the “follow-your-nose” algorithm, etc.

Out of Scope

Some features are explicitly out of scope for the Working Group

• Changing the fundamentals RDF(S) semantics (e.g., usage of model theoretical semantics, interpretation of blank nodes). Note that minor improvements may be required by some of the work in the scope of the Working Group, which is still in the scope of the work.
• Removing current restrictions in the RDF model (e.g., literals not allowed as subjects, or blank nodes as predicates)