PROPOSED RML Working Group Charter

The mission of the RML Working Group is to define an extension of the R2RML language to allow generation of RDF from other data formats beyond relational databases.

Join the RML Working Group.

This proposed charter is available on GitHub. Feel free to raise issues.

Start date [dd monthname yyyy] (date of the "Call for Participation", when the charter is approved)
End date [dd monthname yyyy] (Start date + 2 years)
Chairs [chair name] (affiliation)
Team Contacts Pierre-Antoine Champin (0.1 FTE)
Meeting Schedule Teleconferences: 1 hour calls to be held weekly; extra topic-specific calls may also be held
Face-to-face: face-to-face meetings may be scheduled by consent of the participants, usually no more than 2 per year.

Motivation and Background

RML (RDF Mapping Language) is an extension of R2RML that was intially proposed in 2014 by Anastasia Dimou et al., proving a way to generate RDF graphs from data formats beyond RDB. Other extension were also proposed to declare transformation functions within the mappings (R2RML-F proposed by Christophe Debruyne and Declan O'Sullivan), or to generate RDF graphs from non-relational databases (xR2RML by Franck Michel et al.). Among all these extensions, RML has become quite popular, with currently more than 8 implementations widely used in industry and academic projects. The Knowledge Graph Construction W3C Community Group was formed in 2019 to gather feedback, use-cases, and explore how to merge all extension in one integrated specification maintaining backwards compatilibity with R2RML.

Scope

The scope of this Working Group is to define a declarative language for the construction of RDF graphs from heterogeneous data sources. Building on the foundational concepts of R2RML, RML provides a complementary specification, designed to support mappings from a wide variety of (semi-)structured data formats into RDF. Beyond data formats, RML also provides support for new features: i) flexible declaration of input and output formats; ii) declarative description of transformation functions; iii) enable the generation of RDF Collections & Containers; and iv) declaration of views over any kind of data format for complex data pipelines.

The Knowledge Graph Construction Community Group has identified, in its final report, a set of modules that together constitute the complete RML specification. Each module comprises a distinct set of RDF-related features and can be implemented independently. The Working Group may however reconsider this and proceed differently from the Community Group's proposal. The Working Group will also consider allowing new features in these recommendations, according to Section 6.3.11.4 of the W3C process, in order to render future evolutions easier.

The group MUST ensure that any R2RML mapping can be expressed as a valid RML mapping, and that any RML mapping restricted to the R2RML feature set can be translated back into a valid R2RML mapping.

Out of Scope

The following features are out of scope, and will not be addressed by this Working group.

  • Adding extensions or new features to R2RML or Direct Mapping. These two recommendations will remain stable, without incorporating new features or deprecating any of the existing ones.

Deliverables

Updated document status is available on the group publication status page.

Draft state indicates the state of the deliverable at the time of the charter approval. Expected completion indicates when the deliverable is projected to become a Recommendation, or otherwise reach a stable state.

Normative Specifications

The Working Group will deliver the following W3C normative specifications:

RML-Core: RDF Mapping Language - Core

This specification defines the principal characteristics of the language, generalizing and refining R2RML; the rest of specifications build on top of it. RML-Core consists of almost the same concepts as the R2RML, but redefines them to distinguish them from the R2RML counterparts. It also incoporates new features missing in R2RML such the dynamic generation of language tags or datatypes.

Draft state: Adopted from Knowledge Graph Construction CG

Expected completion: WG-START + 12 months

Adopted Draft: RML-Core, Final Community Group Report (2025-10-31) / RML-Star, Final Community Group Report (2025-10-31)

RML-IO: RDF Mapping Language - Input/Output

This specification defines how input data sources are described and accessed, how their contents are interpreted through reference formulations, and how iteration patterns are applied to traverse them. In addition, it specifies how the output writer can be declared, enabling the consistent description of both the sources from which data is retrieved and the destinations to which RDF is generated.

Draft state: Adopted from Knowledge Graph Construction CG

Expected completion: WG-START + 18 months

Adopted Draft: RML-IO, Final Community Group Report (2025-10-31)

RML-FNML: RDF Mapping Language - Functions

This specification defines This specification defines how data transformation functions can be declaratively expressed and evaluated within RML. It provides a framework to describe functions, their parameters, inputs, and outputs in a processor-independent manner, ensuring interoperability across implementations. By introducing dedicated constructs for function execution and result mapping, this specification enables the seamless integration of data transformation functions into mappings.

Draft state: Adopted from Knowledge Graph Construction CG

Expected completion: WG-START + 24 months

Adopted Draft: RML-FNML, Final Community Group Report (2025-10-31)

RML-CC: RDF Mapping Language - Collections and Containers

This specification defines support for RDF Collections and Containers in RML. It introduces mechanisms to gather values from one or more term maps, manage the creation of empty or nested collections and containers, group heterogeneous term types, and use collections or containers as subjects with assigned identifiers. The functionality requires significant implementation effort, and is therefore specified as a separate module complementing RML-Core.

Draft state: Adopted from Knowledge Graph Construction CG

Expected completion: WG-START + 24 months

Adopted Draft: RML-CC, Final Community Group Report (2025-10-31)

RML-LV: RDF Mapping Language - Logical Views

This specification defines mechanisms to construct RDF datasets from nested input data, to join across multiple data sources and hierarchies, and to integrate data from heterogeneous formats. It introduces the notion of a logical view: a flattened, format-agnostic representation over one or more sources. In addition, it provides means to express relationships between sources and to enrich their fields with structural annotations.

Draft state: Adopted from Knowledge Graph Construction CG

Expected completion: WG-START + 24 months

Adopted Draft: RML-LV, Final Community Group Report (2025-10-31)

YARRRML: YAML RDF Mapping Language

YARRRML is a human readable text-based representation for the RDF mapping language. It is a subset of YAML, a widely used data serialization language designed to be human-friendly. .

Draft state: Adopted from Knowledge Graph Construction CG

Expected completion: WG-START + 24 months

Adopted Draft: YARRRML, Final Community Group Report (2025-10-31)

The Working Group will maintain the following W3C specifications
R2RML: RDB to RDF Mapping Language

Other Deliverables

Other non-normative documents may be created such as:

  • Use case and requirement documents;
  • Test suite and implementation report for the specification;
  • Primer or Best Practice documents to support web developers when designing applications.

Timeline

  • March 2026: First teleconference
  • Q4 2026: FPWD of all deliverables
  • Q1 2027: Candidate Recomendation of RML-core deliverable
  • Q2 2027: Recomendation of RML-core deliverable
  • Q3 2027: Candidate Recomendation of RML-IO/CC/LV/FNML deliverables
  • Q4 2027: Recomendation of RML-IO/CC/LV/FNML deliverables
  • Q4 2027: Candidate Recomendation of YARRRML deliverable
  • Q1 2028: Recomendation of YARRRML deliverable

Success Criteria

In order to advance to Proposed Recommendation, each normative specification is expected to have at least two independent interoperable implementations of every feature defined in the specification, where interoperability can be verified by passing open test suites, and two or more implementations interoperating with each other. In order to advance to Proposed Recommendation, each normative specification must have an open test suite of every feature defined in the specification.

There should be testing plans for each specification, starting from the earliest drafts.

Coordination

For all specifications, this Working Group will seek horizontal review for accessibility, internationalization, privacy, and security with the relevant Working and Interest Groups, and with the TAG. Invitation for review must be issued during each major standards-track document transition, including FPWD. The Working Group is encouraged to engage collaboratively with the horizontal review groups throughout development of each specification. The Working Group is advised to seek a review at least 3 months before first entering CR and is encouraged to proactively notify the horizontal review groups when major changes occur in a specification following a review.

Additional technical coordination with the following Groups will be made, per the W3C Process Document:

W3C Groups

RDF & SPARQL Working Group
RML must remain compatible with the evolving RDF data model and serialization formats, particularly with respect to the representation and generation of RDF-star triples.
JSON-LD Working Group
RML-IO should remain aligned with the evolving JSON-LD specifications to ensure that output graphs generated by RML mappings produce consistent and standards-compliant JSON-LD serializations.
Knowledge Graph Community Group
To synchronize with other incubation and standardization work related to RML, for example RML-IO registry.

Participation

To be successful, this Working Group is expected to have 6 or more active participants for its duration, including representatives from the key implementors of this specification, and active Editors and Test Leads for each specification. The Chairs, specification Editors, and Test Leads are expected to contribute half of a working day per week towards the Working Group. There is no minimum requirement for other Participants.

The group encourages questions, comments and issues on its public mailing lists and document repositories, as described in Communication.

The group also welcomes non-Members to contribute technical submissions for consideration upon their agreement to the terms of the W3C Patent Policy.

Participants in the group are required (by the W3C Process) to follow the W3C Code of Ethics and Professional Conduct.

Communication

Technical discussions for this Working Group are conducted in public: the meeting minutes from teleconference and face-to-face meetings will be archived for public review, and technical discussions and issue tracking will be conducted in a manner that can be both read and written to by the general public. Working Drafts and Editor's Drafts of specifications will be developed in public repositories and may permit direct public contribution requests. The meetings themselves are not open to public participation, however.

Information about the group (including details about deliverables, issues, actions, status, participants, and meetings) will be available from the RML Working Group home page.

Most RML Working Group teleconferences will focus on discussion of particular specifications, and will be conducted on an as-needed basis.

This group primarily conducts its technical work on the public mailing list public-[email-list]@w3.org (archive) and on GitHub issues. The public is invited to review, discuss and contribute to this work.

The group may use a Member-confidential mailing list for administrative purposes and, at the discretion of the Chairs and members of the group, for member-only discussions in special cases when a participant requests such a discussion.

Decision Policy

This group will seek to make decisions through consensus and due process, per the W3C Process Document (section 5.2.1, Consensus). Typically, an editor or other participant makes an initial proposal, which is then refined in discussion with members of the group and other reviewers, and consensus emerges with little formal voting being required.

However, if a decision is necessary for timely progress and consensus is not achieved after careful consideration of the range of views presented, the Chairs may call for a group vote and record a decision along with any objections.

To afford asynchronous decisions and organizational deliberation, any resolution (including publication decisions) taken in a face-to-face meeting or teleconference will be considered provisional. A call for consensus (CfC) will be issued for all resolutions (for example, via email, GitHub issue or web-based survey), with a response period from one week to 10 working days, depending on the chair's evaluation of the group consensus on the issue. If no objections are raised by the end of the response period, the resolution will be considered to have consensus as a resolution of the Working Group.

All decisions made by the group should be considered resolved unless and until new information becomes available or unless reopened at the discretion of the Chairs.

This charter is written in accordance with the W3C Process Document (Section 5.2.3, Deciding by Vote) and includes no voting procedures beyond what the Process Document requires.

Patent Policy

This Working Group operates under the W3C Patent Policy (Version of 15 September 2020). To promote the widest adoption of Web standards, W3C seeks to issue Web specifications that can be implemented, according to this policy, on a Royalty-Free basis. For more information about disclosure obligations for this group, please see the licensing information.

Licensing

This Working Group will use the W3C Software and Document license for all its deliverables.

About this Charter

This charter has been created according to section 3.4 of the Process Document. In the event of a conflict between this document or the provisions of any charter and the W3C Process, the W3C Process shall take precedence.

Charter History

The following table lists details of all changes from the initial charter, per the W3C Process Document (section 4.3, Advisory Committee Review of a Charter):

Charter Period Start Date End Date Changes
Initial Charter [dd monthname yyyy] [dd monthname yyyy] none

Change log

Changes to this document are documented in this section.