Re: [ANN] Shape Expressions 2.1 release candidate

As far as I can tell these documents have had no review within the group.
If so, there is something seriously wrong.  Revisions to group
documents should be receiving expert review within the group before
they are sent out for external or general review.  I do not consider
these documents ready for release until they have received expert
review from within the group.  Nonetheless, I started a review and
here are some comments.


This is a review of https://shexspec.github.io/shape-map/ dated 30
January 2019 which I take to be the current draft of the definition of
ShapeMaps.

The discussion of triple patterns mentions "a known token to identify
the focus node".  I don't see any discussion of how this is done.  The
phrase "known token" does not appear anywhere else in the document.

There is no definition of "match", needed to turn a query ShapeMap
into a fixed ShapeMap.  (Of course, this is almost certainly taken
from SPARQL, but there needs to be an explicit statement to this
effect.  I'm going to go out on a limb and make the assumption that
"match" is taken appropriately from SPARQL.)

It should be stated somewhere that ShapeMaps can contain actual RDF
nodes, which can be blank nodes (and not blank node IDs).  What is the
syntax for this?  It doesn't show up in the ShapeMap grammar.

It is still the case that the map from query ShapeMaps to fixed
ShapeMaps might fail.  This problem needs to be addressed.

With all the problems above there doesn't seem to be any reason for me
to even look at the longer document.




I pullled out an exchange about ShapeMaps from previous email:

> Iovka
> > pfps
>
> > ShapeMaps cannot have two shape associations with the same nodeSelector
and
> > shapeLabel. But the notion of identity for shape associations is not
> > explicitly defined. However, the second half of Example 1 indicates that
> > shape associations have an identity independent of their membership.
This
> > means that the process of converting a query ShapeMap to a fixed
ShapeMap
> > defined in Section 4 of ShapeMap Structure and Language Draft Community
> > Group Report 13 July 2017 at
http://shex.io/shape-map/#dfn-fixed-shapemap
> > might not produce a valid ShapeMap. This needs to be fixed.
>
> The requirement that no two shape associations in a ShapeMap may have the
same combination of node and shape simply ensures that a fixed ShapeMap is
a non-redundant representation of a set of pairs of the form (node, label).
The identity of shape association is very naturally the pair (node, label)
that it represents.
>
> As for the process of converting a query ShapeMap to a fixed ShapeMap, I
do not see how it might produce an invalid ShapeMap: the query ShapeMap
does not specify a status, so even though the same (node, label) is added
multiple times during the conversion, it will be represented only once.

It appears that you are not even bothering to read the documents of
the group.  The second part of Example 1 has a ShapeMap with two
identical shape associations that is clearly stated as invalid.  So
it is definitely the case that adding the same (node, label) multiple
times does indeed end with an invalid ShapeMap.

Peter F. Patel-Schneider