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Re: Thoughts on the LDS WG chartering discussion

From: Ivan Herman <ivan@w3.org>
Date: Fri, 11 Jun 2021 08:51:35 +0200
Cc: Semantic Web <semantic-web@w3.org>, Manu Sporny <msporny@digitalbazaar.com>
Message-Id: <5AD7725D-3326-4A15-ACC1-A611C968F54C@w3.org>
To: David Booth <david@dbooth.org>

> On 11 Jun 2021, at 01:13, David Booth <david@dbooth.org> wrote:
> On 6/10/21 11:08 AM, Ivan Herman wrote:
>>> On 10 Jun 2021, at 16:13, David Booth <david@dbooth.org I still feel like I am somehow missing a fundamental assumption that others are making and I have not yet been able to identify.
>> I wonder whether the misunderstanding is not the following: how do you calculate the canonical N-Quads? What will be the bnode labels?
> Certainly they need to be canonicalized using an algorithm like URDNA2015 or Aidan's algorithm.  Otherwise it would not be canonical N-Quads!
>> What the canonicalization algorithm does is to calculate the canonical bnode labels. I guess you could describe the algorithm as working on a quad representation of the RDF dataset, essentially transforming the quads by relabeling the bnode labels to a canonical version. But that is mathematically equivalent to making the same calculation on the abstract RDF data model. In this respect, the n-quads and the abstract model is essentially equivalent…
> Okay, I didn't realize you were viewing the abstract canonicalization and the canonical N-Quads serialization as essentially equivalent, since
> the Explainer document makes a point of distinguishing them: "Canonicalization, as used in the context of this document and the proposed charter, is indeed defined on an abstract data model (i.e., on RDF Dataset [rdf11-concepts]), regardless of a specific serialization."  In short, it sounds like we agree that only an N-Quads canonicalization is *necessary*, but you view the N-Quads canonicalization as essentially equivalent to an abstract RDF Dataset canonicalization.
> Also, I should perhaps point out (though this is a bit pedantic) that canonicalization really only applies to serialization anyway, because blank node labels do not exist in abstract RDF Datasets.   This fact was the source of some of my puzzlement when I read the proposed charter, because the charter and the Explainer talk about canonicalizing the abstract RDF Dataset. But I eventually managed to convince myself that the charter and explainer were just being slightly sloppy in terminology.  In reality, the proposed abstract canonicalization algorithm does not produce a canonicalized RDF Dataset; rather it produces a pair: an isomorphic RDF Dataset and a bijection from the blank nodes in that dataset to a set of blank node *labels*. Fortunately, the "RDF Dataset Canonicalization" document is a bit more precise about this.
> https://json-ld.github.io/rdf-dataset-canonicalization/spec/index.html

You are right. Can you suggest a clearer way of putting this into the charter (or the explainer) without going into to excessive details on the charter level? 

> The other thing that I still fundamentally do not yet grasp about the proposed charter is this: Why is it restricted to RDF source documents?   Clearly the canonicalization algorithm is about RDF, so that much I understand.  But for the digital signature vocabulary, why wouldn't it also be useful to be able to sign, say, a PDF document?

Well… I cannot really answer this, Manu might. It may be correct that the vocabulary expressing the signature in RDF could be applied to _anything_, or at least to anything that has a URL. And that may be a site-effect of the work but, afaik, the original work always concentrated on RDF, so this never came up.

I would be perfectly happy if the document the WG produces would explore this avenue in some way or other. I would not think we should put this into the charter, though: it may lead to extra complications that we do not necessarily foresee, and would therefore become out of scope.

But I would let Manu react on this more.



> Why should the RDF signing vocabulary be limited to talking about RDF documents?  Or am I misunderstanding the intent here?   Perhaps if there were a simple, complete example, it would help.  Again, I feel like I am missing some of the assumed context.
> Thanks,
> David Booth

Ivan Herman, W3C 
Home: http://www.w3.org/People/Ivan/
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Received on Friday, 11 June 2021 06:52:04 UTC

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