Arnaud's Blog

Opinions on open source, standards, and other things

Update on the W3C LDP specification

What just happened

The W3C LDP Working Group just published another Last Call draft of the Linked Data Platform (LDP) specification.

This specification was previously a Candidate Recommendation (CR) and this represents a step back – sort of.

Why it happened

The reason for going back to Last Call, which is before Candidate Recommendation on the W3C Recommendation track, is primarily because we are lacking implementations of the IndirectContainer.

Candidate Recommendation is a stage when implementers are asked to go ahead and implement the spec now considered stable, and report on their implementations. To exit CR and move to Proposed Recommendation (PR), which is when the W3C membership is asked to endorsed the spec as a W3C Recommendation/standard, every feature in the spec has to have two independent implementations.

Unfortunately, in this case, although most of the spec has been implemented by at least two different implementations (see the implementation report) IndirectContainer has not. Until this happens, the spec is stuck in CR.

We do have one implementation and one member of the WG said he plans to implement it too. However, he couldn’t commit to a specific timeline.

So, rather than taking the chance of having the spec stuck in CR for an indefinite amount of time the WG decided to republish the spec as a Last Call draft, marking IndirectContainer has a “feature at risk“.

What it means

When the Last Call period review ends in 3 weeks (on 7 October 2014) either we will have a second implementation of IndirectContainer and the spec will move to PR as is (skipping CR because we will then have two implementations of everything), or we will move IndirectContainer to a separate spec that can stay in CR until there are two implementations of it and move the remaining of the LDP spec to PR (skipping CR because we already have two implementations).

I said earlier publishing the LDP spec as a Last Call was a “step back – sort of” because it’s really just a technicality. As explained above, this actually ensures that, either way, we will be able to move to PR (skipping CR) in 3 weeks.

Bonus: Augmented JSON-LD support

When we started 2 years ago, the only the serialization format for RDF that was standard was RDF/XML. Many people disliked this format, which is arguably responsible for the initial lack of adoption of RDF, so the WG decided to require that all LDP servers support Turtle as a default serialization format – Turtle was in the process of becoming a standard. The WG got praised for this move which, at the time, seemed quite progressive.

Yet, a year and a half later, during which we saw the standardization of JSON-LD, requiring Turtle while leaving out JSON-LD no longer appeared so “bleeding edge”. At the LDP WG Face to Face meeting in Spring, I suggested we encourage support for JSON-LD by adding it as a “SHOULD”. The WG agreed. Some WG members would have liked to make it a MUST but this would have required going back to Last Call and as for one, as chair of the WG responsible for keeping the WG on track to deliver a standard on time, didn’t think this was reasonable.

Fast forward to September, we now found ourselves having to republish our spec as a Last Call draft anyway (because of the IndirectContainer situation).  We seized the opportunity to increase support for JSON-LD by requiring LDP servers to support it (making it a MUST).

Please, send comments to and implementation reports to

Lesson learned

I wish we had marked IndirectContainer as a feature at risk when we moved to Candidate Recommendation back in June. Already then we knew we might not have enough implementations of it to move to PR. If we had marked it as a feature at risk we could now just go to PR without it and without any further delay.

This is something be remembered: when in doubt, just mark things “at risk”. There is really not much downside to it and it’s a good safety valve to have.


September 16, 2014 - Posted by | standards | , ,

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