W3C home > Mailing lists > Public > public-credentials@w3.org > May 2016

Re: Updated data model specification document

From: Steven Rowat <steven_rowat@sunshine.net>
Date: Sat, 28 May 2016 10:28:48 -0700
To: public-credentials@w3.org
Message-ID: <fd3ec6b5-9755-90cb-0718-bd4f9e38d011@sunshine.net>
Dave,
Thank you for the extensive explanation. I read it, slept on it, read 
it again, read some about RDF triples to refresh my memory about 
triple semantics, and tried to read the VC data model page again 
(http://opencreds.org/specs/source/claims-data-model/). I got a little 
further this time before confusion, but not all the way through.

I'm beginning to understand some parts better, but the core 
architecture is eluding me.

I'm going to explain below my concerns about how 'properties' are used 
in the VC data model, which is the first major issue I run into that 
blocks me. Perhaps if I can understand it then the rest will follow.

On 5/27/16 6:41 PM, Dave Longley wrote:
> The "id" property is a bit special. To understand that I'll try to
> provide more on my view of the data model.
>
> The data model can be understood as a graph. It can be thought of as a
> collection of nodes that are connected to other nodes via "properties".
>
> Each of these relations in the graph can be modeled as a statement with
> a subject, a property, and an object.

I think this triple is the core of my problem with the word 'property' 
in the data model. That is: isn't the use of the word 'property' 
misleading: using 'property' for a relation between a subject and an 
object?

Because a property is commonly meant to be attached to a single 
'thing', not the relation between two 'things'. The Random House 
definitions of 'property' and 'relation' make this clear:

Property:
4. a basic, essential, or special quality of a thing

Relation:
1. association between or among things; connection; relationship

Question: are you in fact using 'Property' as the second term in a 
triple? Like in RDF,
subject->predicate->object.

(From Wikipedia "...triples in RDF terminology. The subject denotes 
the resource, and the predicate denotes traits or aspects of the 
resource and expresses a relationship between the subject and the 
object.")

I may misunderstand the overall VC data model at some other level, but 
in the way I'm attempting to understand it, 'property' seems 
misleading, if being used to denote a relationship between two 
'things' or 'nodes'. To follow common English usage, the 'property' 
should belong to either the subject node, or the object node, not 
designate the relation between them.


> The value for "id" may be a URL that globally
> identifies the subject. Every other property defines a relation between
> the subject and an object.

Same concern as above. Of course you could redefine the word 
'property'--and perhaps you have--to mean 'relationship' in the 
specific context of the VC data model, but it seems counter-intuitive 
to do this (since the wider world doesn't use it this way) unless 
unless there's a special reason (which I'm not understanding yet) as 
to why this redefinition is appropriate.

If there is such a reason, I'd really really like to know what it is. 
:-) :-)


Steven

p.s. Sometimes a simple-as-possible block flow-diagram is the best way 
to get the basic architecture across. Is it possible someone could 
make one of those for the VC data model?
Received on Saturday, 28 May 2016 17:29:18 UTC

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