I really don't see the issue here. SHACL, like ShEx is a language to
express data shapes. I adopted using ShEx in a wikidata context 2016 when
ShEx was demonstrated at a tutorial at the SWAT4HCLS conference [1] in
Amsterdam, where it was discussed in both a tutorial and a hackathon topic.
At that conferene, I was convinced that ShEx is helpful in maintaining
quality in Wikidata. ShEx offers not only the means to validate data shapes
in Wikidata, but it also provides a way to document how primary data is
expressed in Wikidata. In 2016 I joined the ShEx community group [2].
Since I have been actively using ShEx in defining shapes in various
projects on Wikidata (e.g. Gene Wiki and Wikicite). It is not that this
happened in secrecy. On the contrary, it was discussed at both Wikimedia
[3,4] and non-Wikimedia events [5,6,7].
It is also not the case that SHACL has not been discussed in this context,
on the contrary, I have very good memories of a workshop where both were
debated (see page 24 ;) ) [8]
IMHO the statement that we all should adhere to one standard, simply
because it is a standard, is not a valid argument. Imagine having to
dictate that we all should speak English because it is the standard
language. In every single talk that I have given since 2016, proponents of
SHACL have been very vocal in asking the same question over and over again
"why not SHACL?", where the discussion never went beyond, "You should
because it is a standard". It is also a bit disingenuous to suggest we all
should adhere to SHACL because it is the standard, while in the same
sentence calling it a "Recommendation".
Although initially, I was open to SHACL as well (I use both Mac and Linux,
so why not open up to different alternatives in data shapes), (Some)
Arguments for me to prefer ShEx over SHACL are:
1. Already in 2017 there were different (open) implementations. At the time
SHACL didn't have much tooling to choose from, other than one javascript
implementation and a proprietary software package.
2. ShEx has a more intuitive way of describing Shapes, which is the compact
syntax (ShExC). SHACL seems to have adopted the compact syntax as well, but
only yesterday [9].
3. The culture in the Shape Expression community group aligns well with the
culture in Wikidata.
4. I don't want to be shackled to one standard (pun intended). I assume the
name was chosen with a shackle in mind, which puts constraints at the core
of the language. Wikidata already has different methods in place to deal
with constraints and constraint violations. In the context of Wikidata,
ShEx should specifically not be intended to impose constraints, on the
contrary, it allows expressing of disagreement or variants of different
shapes, whether conflict or not. Which fits well with the NPOV concept.
Symbols do matter.
For a less personal comparison, I refer to the "Validating RDF data" book
which describes both ShEx and SHACL, and has a specific chapter on how they
compare and differ [10]
Up until now, I have been using ShEx in repositories outside the Wikidata
ecosystem (e.g. Github), but I am really excited about the release of this
extension. I am curious about how the wiki extension will influence the
maintenance of schemas. Schemas are currently often expressed as static
images, while in practice the schemas are as fluid as the underlying data
itself. Being able to document these changes dynamically (the wiki way),
can be very interesting. One specific expectation I have is that it might
make it easier to write federated SPARQL queries. Currently, when writing
these federated queries we often have to rely on either a set of example
queries or a one-time schema description, which makes it hard to write
those queries, because of schemas changing constantly. Federated SPARQL
queries now really is a process of "slot machine" querying, where one has
to explore the underlying schema, query by query. With a wiki in place and
a community maintaining these ever-changing schema's, I expect better
documentation.
The data shape community, instead of adhering to one language, should
really be proud to have produced two very helpful languages. ShEx and SHACL
are similar but do have differences so both have merit to exist and I wish
we could steer away from this ShEx vs SHACL feud. It really isn't helping
the cause, i.e. being able to express schemas in a formal language.
Honestly, this fued really reminds me of the famous monty python sketch,
"The machine that says Bing". Let us focus on the patient and not on the
"Bing".
Just my 2ct.
[1]
http://www.swat4ls.org/workshops/amsterdam2016/
[2]
https://www.w3.org/community/shex/
[3]
https://www.wikidata.org/wiki/Wikidata:WikidataCon_2017/Submissions/Using_S…
[4]
https://meta.wikimedia.org/wiki/WikiCite_2017/Program
[5]
https://figshare.com/articles/Using_Shape_Expressions_ShEx_to_model_validat…
[6]
https://2017.semantics.cc/satellite-events/linked-data-quality-assessment-a…
[7]
http://swib.org/swib18/programme.html
[8]
https://upload.wikimedia.org/wikipedia/commons/d/d6/WikiCite_2017_report.pdf
[9]
https://lists.w3.org/Archives/Public/public-shacl/2019May/0012.html
[10]
http://book.validatingrdf.com/
On Wed, May 29, 2019 at 10:05 PM Antoine Zimmermann <
antoine.zimmermann(a)emse.fr> wrote:
Hello,
Could you explain why the non-standard ShEx has been chosen rather than
the W3C Recommendation SHACL?
I would assume that if one has several options for bringing a
functionality to something that largely promotes interoperability (like
Wikidata), the default choice should be a standard, and /only if/ one
has a carefully crafted argumentation to reject it, one would opt for
something else.
For those who may not know, the W3C RDF Data Shapes Working Group worked
between 2014 and 2017 on defining a standard for describing data shapes
in RDF. ShEx existed already and was a candidate for standardisation.
Eventually, another standard emerged, Shapes Constraint Language (SHACL,
see
https://www.w3.org/TR/shacl/).
Disclaimer: I did not contribute to either SHACL or ShEx, and I do not
know them enough to judge which one is better.
Best,
--AZ
On 19/05/2019 15:32, Léa Lacroix wrote:
Hello all,
After several months of development and testing together with the
WikiProject ShEx
<https://www.wikidata.org/wiki/Wikidata:WikiProject_ShEx>, Shape
Expressions are about to be enabled on Wikidata.
*First of all, what are Shape Expressions?*
ShEx (Q29377880) <https://www.wikidata.org/wiki/Q29377880> is a
concise,
formal modeling and validation language for RDF
structures. Shape
Expressions can be used to define shapes within the RDF graph. In the
case of Wikidata, this would be sets of properties, qualifiers and
references that describe the domain being modeled.
See also:
* a short video about ShEx
<https://www.youtube.com/watch?v=AR75KhEoRKg> made by community
members during the Wikimedia hackathon 2019
* introduction to ShEx <http://shex.io/shex-primer/>
* more details about the language <http://shex.io/shex-semantics/>
*What can it be used for?*
On Wikidata, the main goal of Shape Expressions would be to describe
what the basic structure of an item would be. For example, for a human,
we probably want to have a date of birth, a place of birth, and many
other important statements. But we would also like to make sure that if
a statement with the property “children” exists, the value(s) of this
property should be humans as well. Schemas will describe in detail what
is expected in the structure of items, statements and values of these
statements.
Once Schemas are created for various types of items, it is possible to
test some existing items against the Schema, and highlight possible
errors or lack of information. Subsets of the Wikidata graph can be
tested to see whether or not they conform to a specific shape through
the use of validation tools. Therefore, Schemas will be very useful to
help the editors improving the data quality. We imagine this to be
especially useful for wiki projects to more easily discuss and ensure
the modeling of items in their domain. In the spirit of Wikidata not
restricting the world, Shape Expressions are a tool to highlight, not
prevent, errors.
On top of this, one could imagine other uses of Schemas in the future,
for example building a tool that would suggest, when creating a new
item, what would be the basic structure for this item, and helping
adding statements or values. A bit like this existing tool, Cradle
<https://tools.wmflabs.org/wikidata-todo/cradle/#/>, that is currently
not based on ShEx.
*What is going to change on Wikidata?*
* A new extension will be added to Wikidata: EntitySchema
<https://www.mediawiki.org/wiki/Extension:EntitySchema>, defining
the Schema namespace and its behavior as well as special pages
related to it.
* A new entity type, EntitySchema, will be enabled to store Shape
Expressions. Schemas will be identified with the letter E.
* The Schemas will have multilingual labels, descriptions and aliases
(quite similar to the termbox on Items), and the schema text one can
fill with a syntax called ShEx Compact Syntax (ShExC)
<http://shex.io/shex-semantics/#shexc>. You can see an example here
<https://wikidata-shex.wmflabs.org/wiki/EntitySchema:E2>.
* The external tool shex-simple
<
https://tools.wmflabs.org/shex-simple/wikidata/packages/shex-webapp/doc/she…
is directly linked from the Schema pages in order to check entities
of your choice against the schema.
*When is this happening?*
Schemas will be enabled on on
test.wikidata.org
<http://test.wikidata.org> on May 21st and on
wikidata.org
<http://wikidata.org> on May 28th. After this release, they will be
integrated to the regular maintenance just like the rest of Wikidata’s
features.
*How can you help?*
* Before the release, you can try to edit or create Shape Expressions
on our test system <https://wikidata-shex.wmflabs.org/wiki/Main_Page
* If you find any issue or feature you’d like to have, feel free to
create a new task on Phabricator with the tag |shape-expressions|
* Once Schemas are enabled, you can discuss about it on your favorite
wikiprojects: for example, what types of items would you like to
model?
* You can also get more information about how
to create a Schema
<
https://www.wikidata.org/wiki/Wikidata:WikiProject_ShEx/How_to_get_started%…
*See also: *
* Main Phabricator board
<https://phabricator.wikimedia.org/tag/shape_expressions/>
* Technical documentation of the extension
<https://meta.wikimedia.org/wiki/Extension:EntitySchema>
* To enhance the interface, you can use this user script
<
https://www.wikidata.org/wiki/User:Zvpunry/EntitySchemaHighlighter.js>
to highlight items and properties in the
schema code and turn the
IDs into links
If you have any questions, feel free to reach me. Cheers,
--
Léa Lacroix
Project Manager Community Communication for Wikidata
Wikimedia Deutschland e.V.
Tempelhofer Ufer 23-24
10963 Berlin
www.wikimedia.de <http://www.wikimedia.de>
Wikimedia Deutschland - Gesellschaft zur Förderung Freien Wissens e. V.
Eingetragen im Vereinsregister des Amtsgerichts Berlin-Charlottenburg
unter der Nummer 23855 Nz. Als gemeinnützig anerkannt durch das
Finanzamt für Körperschaften I Berlin, Steuernummer 27/029/42207.
_______________________________________________
Wikidata mailing list
Wikidata(a)lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikidata
_______________________________________________
Wikidata mailing list
Wikidata(a)lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikidata