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Re: Template language for SPARQL?

From: David Booth <david@dbooth.org>
Date: Fri, 27 Jul 2012 09:37:14 -0400
To: Austin William Wright <aaa@bzfx.net>
Cc: semantic-web <semantic-web@w3.org>
Message-ID: <1343396234.2725.44865.camel@dbooth-laptop>
Hi Austin,

On Fri, 2012-07-27 at 05:11 -0700, Austin William Wright wrote:
> 
> On Thu, Jul 26, 2012 at 1:06 PM, David Booth <david@dbooth.org> wrote:
>         There doesn't seem to be any sort of community consensus on
>         preferred
>         syntax for indicating parameters in a SPARQL template.
>          Several syntaxes
>         were mentioned:
>         
>           {?foo}  %{foo}  %2  $foo  ${foo}
>  
> I'll echo Steve Harris's concerns about security. 

Yes, in fact, now that you mention it I think I will make the warning in
the man page about this a bit more prominent.

> You shouldn't place variables inside string literals, that's asking
> for trouble. 

Yes it is, so anyone using this template processor must be aware that
those dangers exist if they choose to use it that way.  I included one
example of such dangers in the man page:

       Also, although bare words (or numbers!) are allowed as variable names,
       they are usually not a good idea, because it is too easy to make a
       mistake like writing the following:

         #inputs( givenName )
         SELECT *
         WHERE { ?name foaf:givenName "givenName" }

       which, when givenName has the value "Bill", will silently become:

         SELECT *
         WHERE { ?name foaf:Bill "Bill" }

       which is probably NOT what you intended.

> Why invent a new variable/placeholder when one already exists? Almost
> certainly you should be passing a raw query, and binding values onto
> variables at query-time, or some equivalent if you can't do this on
> the query engine level:
> 
> var query = SPARQLSubstitute( "SELECT * { ?president
> foaf:givenName ?firstName;  foaf:familyName ?lastName. }" ,
> {firstName: "Bill", lastName:"Clinton"} );

Yes, if you can get by with merely binding values to variables, then
existing SPARQL mechanisms are definitely preferable.  But this template
processor was designed to be able to handle cases that cannot be done
that way, such as changing graph names in graph operations, or filling
in a WHERE clause with an entire path of predicates.
> 
> For instance, modify a SPARQL lexer/parser to parse the query string
> for particular variables, and substitute them with the (properly
> escaped) value. No new, special syntax is necessary. You can probably
> get by implementing subset of the SPARQL syntax since if you assume a
> well-formed query, you only need to parse for variables and string
> literals (and maybe comments). Luckily the SPARQL standard publishes a
> fairly readable grammar, I wrote a parser in Javascript for all of
> SPARQL 1.1 in a fairly short amount of time. (I might try this out
> tomorrow.)

That sounds like it could be useful.  But would it give more
functionality than using BINDINGS?

David
> 
> Like you point out, you can't pass variable values over the HTTP query
> protocol, a standard to do this over HTTP is very much needed.


-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Received on Friday, 27 July 2012 13:37:47 UTC

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