Re: What does Substitute() actually do?

[Andy Seaborne]

Substitute works on the algebra, not the query syntax.
QueryTransformOps works on query syntax.

https://afs.github.io/substitute.html is about the SPARQL operation on 
which EXISTS is based.

    Andy

On 06/02/2025 03:24, Nicholas Car wrote:
You could try running that with RDFlib and see what it does….

How is substitute() different to just string template substitution? Is it just 
a convenience function so substitution can be done on a Jena SPARQL object 
(perhaps algebra) rather than a string?

Is that your goal for an RDFLib equivalent?

SPARQL string to/from SPARQL grammar object is handles in RDFLib fine so I 
guess as I think the code says, an RDFLib substitute() could work on either or 
both.

Nick

On Thu, Feb 6, 2025 at 10:05 am, Martynas Jusevičius <[marty...@atomgraph.com](mailto:On 
Thu, Feb 6, 2025 at 10:05 am, Martynas Jusevičius <<a href=)> wrote:

OK I simply fed Jena's source to ChatGPT and asked it to produce an
RDFLIb version :)
No idea if it's correct but I'll find out I guess.

from rdflib import Variable, BNode, Literal
from rdflib.plugins.sparql.algebra import BGP, Filter, Join, LeftJoin,
Union, Graph, Extend, Minus, OrderBy, Project

def substitute(algebra, binding):
if isinstance(algebra, BGP):
new_triples = []
for s, p, o in algebra.triples:
s = binding.get(s, s)
p = binding.get(p, p)
o = binding.get(o, o)
new_triples.append((s, p, o))
return BGP(new_triples)
elif isinstance(algebra, Filter):
new_p = substitute(algebra.p, binding)
new_expr = algebra.expr
for var, val in binding.items():
new_expr = new_expr.substitute(var, val)
return Filter(new_expr, new_p)
elif isinstance(algebra, Join):
return Join(substitute(algebra.p1, binding),
substitute(algebra.p2, binding))
elif isinstance(algebra, LeftJoin):
return LeftJoin(substitute(algebra.p1, binding),
substitute(algebra.p2, binding), algebra.expr)
elif isinstance(algebra, Union):
return Union(substitute(algebra.p1, binding),
substitute(algebra.p2, binding))
elif isinstance(algebra, Graph):
return Graph(algebra.term, substitute(algebra.p, binding))
elif isinstance(algebra, Extend):
new_p = substitute(algebra.p, binding)
new_expr = algebra.expr
for var, val in binding.items():
new_expr = new_expr.substitute(var, val)
return Extend(new_p, new_expr, algebra.var)
elif isinstance(algebra, Minus):
return Minus(substitute(algebra.p1, binding),
substitute(algebra.p2, binding))
elif isinstance(algebra, OrderBy):
return OrderBy(substitute(algebra.p, binding), algebra.expr)
elif isinstance(algebra, Project):
return Project(substitute(algebra.p, binding), algebra.PV)
else:
return algebra

On Thu, Feb 6, 2025 at 12:54 AM Martynas Jusevičius
<marty...@atomgraph.com> wrote:

Hi,

I was looking to implement something like substitute() using RDFLib.

I checked the note:
https://afs.github.io/substitute.htm
But I couldn't find a clear example.

For example, how would this query string (the template)

PREFIX dbo: <http://dbpedia.org/ontology/>
CONSTRUCT
WHERE { ?city dbo:populationTotal ?population }

would look like after substituting (?city,
<http://dbpedia.org/resource/Copenhagen>)?


Martynas