Re: Re: Semantics of SERVICE w.r.t. slicing
Hi Andy,
> Are you going to be making improvements to query
tranformation/optimization as part of your work on the enhanced SERVICE
handling on the active PR?
To summarize the PR (https://github.com/apache/jena/issues/1314) for
readers here: Its about a (a) improving the extension system for custom
service executors and
(b) creating a plugin that allows for bulk retrieval and caching with
SERVICE.
Actually I am trying to avoid touching transformation/optimization, but
as part of my work on SERVICE extensions I added a little
'correlate' option. Together with a 'self' flag for referring back to
the active dataset this allows for doing:
# For each department fetch 5 employees
SELECT * {
?d a . Department
SERVICE { # self could also be a URI such as
urn:x-arq:self
SELECT ?e { ?d hasEmployee ?e } LIMIT 5
} }
Actually the variable ?d in the SERVICE clause has a different scope,
but if 'correlate' is seen, my plugin just applies
Rename.reverseVarRename on the OpService.
This could be restricted to only the variables that join with the input
binding. This means the scope of (some of) the variables in the SERVICE
clause is lost and a naive substitution with the input bindings becomes
possible.
For example the following query
SELECT * {
BIND( AS ?s)
SERVICE { # self is implied if no other URL is mentioned
SELECT ?x ?y { # Important not no project ?s otherwise VarFinder
will prevent the OpJoin->OpSequence optimization
{ BIND(?s AS ?x) } UNION { BIND(?s AS ?y) } }
} }
Yields:
-
| s | x | y |
=
| | | |
| | | |
-
For completeness, without correlate: one gets:
SELECT * {
BIND( AS ?s)
{ SELECT ?x ?y { { BIND(?s AS ?x) } UNION { BIND(?s AS ?y) } } }
}
-
| s | x | y |
=
| | | |
| | | |
So far, it was possible to trick Jena into optimizing OpJoin into
OpSequence as long as there were no joining variables.
The need for the extra projection of ?x ?y (and not ?s) is not super
nice but it used to be a good tradeoff for not having to touch optimizers
and having this feature escalate into the core of ARQ.
I guess with my recent (bug) report I shot myself somewhat in the foot
now :D
Because I am not sure if its still possible to write a query
syntactically in a way such that OpJoin turns into OpSequence if
LIMIT/OFFSET appears in the service clause!
Consequently, its actually the optimizer that would have to be aware of
the 'correlate' flag on service clauses and base its decision on it.
It just turns out that the SPARQL 1.1 service syntax is the easiest way
to have a syntax for it until hopefully sparql 1.2 standardizes it
(corresponding issue: https://github.com/w3c/sparql-12/issues/100)
Andy recently also raised the option to extend the ARQ parser with
custom syntax |SERVICE <http://my.endpoint/sparql> ARGS "cache" { ... }:|
https://github.com/apache/jena/pull/1315#issuecomment-1146350174
Something along these lines would be very powerful when fleshed out, but
from my side I think for this work its not necessary to add custom
syntax (yet).
But of course the larger picture is how to e.g. extend service with e.g.
http options and other custom options.
(I think there was some discussion on the sparql 1.2 issue tracker but I
can't find it right now).
Cheers,
Claus
On 03.06.22 22:41, Andy Seaborne wrote:
JENA-2332 and PR 1364.
Andy
https://issues.apache.org/jira/browse/JENA-2332
https://github.com/apache/jena/pull/1364
On 03/06/2022 18:29, Andy Seaborne wrote:
Probably a bug then.
Are you going to be making improvements to query
tranformation/optimization as part of your work on the enhanced
SERVICE handling on the active PR?
Andy
On 03/06/2022 10:39, Claus Stadler wrote:
Hi again,
I think the point was missed; what I was actually after is that in
the following query a "join" is optimized into a "sequence"
and I wonder whether this is the correct behavior if a LIMIT/OFFSET
is present.
So running the following query with optimize enabled/disabled gives
different results:
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s
<http://www.w3.org/2000/01/rdf-schema#label> ?x } LIMIT 1 }
}
➜ bin ./arq --query service-query.rq
(sequence !
(service <https://dbpedia.org/sparql>
(slice _ 5
(bgp (triple ?s
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://dbpedia.org/ontology/MusicalArtist>
(service <https://dbpedia.org/sparql>
Re: Re: Semantics of SERVICE w.r.t. slicing
Hi again,
I think the point was missed; what I was actually after is that in the
following query a "join" is optimized into a "sequence"
and I wonder whether this is the correct behavior if a LIMIT/OFFSET is
present.
So running the following query with optimize enabled/disabled gives
different results:
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s
<http://www.w3.org/2000/01/rdf-schema#label> ?x } LIMIT 1 }
}
➜ bin ./arq --query service-query.rq
(sequence !
(service <https://dbpedia.org/sparql>
(slice _ 5
(bgp (triple ?s
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://dbpedia.org/ontology/MusicalArtist>
(service <https://dbpedia.org/sparql>
(slice _ 1
(bgp (triple ?s <http://www.w3.org/2000/01/rdf-schema#label>
?x)
---
| s |
x |
===
| <http://dbpedia.org/resource/Aarti_Mukherjee> | "Aarti
Mukherjee"@en |
| <http://dbpedia.org/resource/Abatte_Barihun> | "Abatte
Barihun"@en |
| <http://dbpedia.org/resource/Abby_Abadi> | "Abby
Abadi"@en |
| <http://dbpedia.org/resource/Abd_al_Malik_(rapper)> | "Abd al
Malik"@de |
| <http://dbpedia.org/resource/Abdul_Wahid_Khan> | "Abdul Wahid
Khan"@en |
---
./arq --explain --optimize=no --query service-query.rq
(join !
(service <https://dbpedia.org/sparql>
(slice _ 5
(bgp (triple ?s
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://dbpedia.org/ontology/MusicalArtist>
(service <https://dbpedia.org/sparql>
(slice _ 1
(bgp (triple ?s <http://www.w3.org/2000/01/rdf-schema#label>
?x)
-
| s | x |
=
-
Cheers,
Claus
On 03.06.22 10:22, Andy Seaborne wrote:
On 02/06/2022 21:19, Claus Stadler wrote:
Hi,
I noticed some interesting results when using SERVICE with a sub
query with a slice (limit / offset).
Preliminary Remark:
Because SPARQL semantics is bottom up, a query such as the following
will not yield bindings for ?x:
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { BIND(?s AS ?x) }
}
The query plan for that is:
(join
(service <https://dbpedia.org/sparql>
(slice _ 5
(bgp (triple ?s
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://dbpedia.org/ontology/MusicalArtist>
(service <https://dbpedia.org/sparql>
(extend ((?x ?s))
(table unit
which has not had any optimization applied. ARQ checks scopes before
doing any transfomation.
Change BIND(?s AS ?x) to BIND(?s1 AS ?x)
and it will have (join) replaced by (sequence)
---
| s | x |
===
| <http://dbpedia.org/resource/Aarti_Mukherjee> | |
| <http://dbpedia.org/resource/Abatte_Barihun> | |
| <http://dbpedia.org/resource/Abby_Abadi> | |
| <http://dbpedia.org/resource/Abd_al_Malik_(rapper)> | |
| <http://dbpedia.org/resource/Abdul_Wahid_Khan> | |
---
LIMIT 1 is a no-op - the second SERVICE always evals to one row of no
columns. Which makes the second SERVICE the join identity and the
result is the first SERVICE.
Column ?x is only in the display because it is in "SELECT *"
Query engines, such as Jena, attempt to optimize execution. For
instance, in the following query,
instead of retrieving all labels, jena uses each binding for a
Musical Artist to perform a lookup at the service.
The result is semantically equivalent to bottom up evaluation
(without result set limits) - just much faster.
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { ?s
<http://www.w3.org/2000/01/rdf-schema#label> ?x }
}
The main point:
However, the following query with ARQ interestingly yields one
binding for every musical artist - which contradicts the bottom-up
paradigm:
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.
Semantics of SERVICE w.r.t. slicing
Hi,
I noticed some interesting results when using SERVICE with a sub query
with a slice (limit / offset).
Preliminary Remark:
Because SPARQL semantics is bottom up, a query such as the following
will not yield bindings for ?x:
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { BIND(?s AS ?x) }
}
Query engines, such as Jena, attempt to optimize execution. For
instance, in the following query,
instead of retrieving all labels, jena uses each binding for a Musical
Artist to perform a lookup at the service.
The result is semantically equivalent to bottom up evaluation (without
result set limits) - just much faster.
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { ?s
<http://www.w3.org/2000/01/rdf-schema#label> ?x }
}
The main point:
However, the following query with ARQ interestingly yields one binding
for every musical artist - which contradicts the bottom-up paradigm:
SELECT * {
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s a
<http://dbpedia.org/ontology/MusicalArtist> } LIMIT 5 }
SERVICE <https://dbpedia.org/sparql> { SELECT * { ?s
<http://www.w3.org/2000/01/rdf-schema#label> ?x } LIMIT 1 }
}
<http://dbpedia.org/resource/Aarti_Mukherjee> "Aarti Mukherjee"@en
<http://dbpedia.org/resource/Abatte_Barihun> "Abatte Barihun"@en
... 3 more results ...
With bottom-up semantics, the second service clause would only fetch a
single binding so in the unlikely event that it happens to join with a
musical artist I'd expect at most one binding
in the overall result set.
Now I wonder whether this is a bug or a feature.
I know that Jena's VarFinder is used to decide whether to perform a
bottom-up evaluation using OpJoin or a correlated join using OpSequence
which results in the different outcomes.
The SPARQL spec doesn't say much about the semantics of Service
(https://www.w3.org/TR/sparql11-query/#sparqlAlgebraEval)
So I wonder which behavior is expected when using SERVICE with SLICE'd
queries.
Cheers,
Claus
--
Dipl. Inf. Claus Stadler
Institute of Applied Informatics (InfAI) / University of Leipzig
Workpage & WebID: http://aksw.org/ClausStadler
Streaming JSON RowSets (JENA-2302)
Dear all, I want to inform you of an active PR for making RowSets over application/sparql-reults+json streaming JIRA: https://issues.apache.org/jira/projects/JENA/issues/JENA-2302 PR: https://github.com/apache/jena/pull/1218 As nowadays JSON is the default content type used in Jena for sparql results, this PR is aimed at easing working with large sparql result sets by having streaming working out-of-the-box. The implementation used by jena so far loaded json sparql result sets into memory first. The JSON format itself allows for repeated keys (where the last one takes precedence) and keys may appear in any order - these things introduce a certain variety in how sparql result sets can be represented and that needs to be handled correctly by the implementation. While the new implementation already succeeds on all existing jena tests, there is still the risk of breaking existing implementations that rely on certain behavior of the non-streaming approach. Therefore, if you think this change might (negatively) affect you then please provide feedback on the proposed PR. Best regards, Claus Stadler -- Dipl. Inf. Claus Stadler Institute of Applied Informatics (InfAI) / University of Leipzig Workpage & WebID: http://aksw.org/ClausStadler
Re: Can RDF star support be deactivated?
Hi Andy,
In the meantime I have upgraded my code and it turned out that it was
essentially the newly introduced visitor method for ElementFind that was
missing in some of my transforrmers
- but that was easy to 'solve' for now by just raising an
UnsupportedOperationException.
Cheers,
Claus
On 2020/09/01 17:42:41, Andy Seaborne wrote:
> Ping?>
>
> I'm not aware of any compile errors for APIs but and return signatures >
> can make it complicated.>
>
> NodeVisitor doesn't include it (probably an omission - but a default >
> method would solve that?>
>
> Andy>
>
> On 28/08/2020 13:33, Andy Seaborne wrote:>
> > >
> > >
> > On 28/08/2020 02:12, cstad...@informatik.uni-leipzig.de wrote:>
> >>>
> >> +1 This is a very good point; I also have around 10 years of active >
> >> code based on Jena and I was not yet able to upgrade to 3.16 because I >
> >> did not find the time to resolve several compile errors which are at >
> >> least partly due to changes introduced for RDF*. And even after the >
> >> upgrade I would most likely run into the similar issues as Holger >
> >> points out.>
> > >
> > Hmm - where are you getting compile errors?>
> > >
> >>>
> >> I have have used the following to work around legacy issues with >
> >> RDF1.0/1.1:>
> >> JenaRuntime.isRDF11 = false;>
> >>>
> >> This might be a good place to allow for a>
> >> JenaRuntime.isRDFStar = false;>
> >>>
> >> Cheers,>
> >> Claus>
> >>>
> >> Quoting Holger Knublauch :>
> >>>
> >>> It's good to see the recently introduced RDF* features in Jena. But >
> >>> as someone with a lot of existing Jena code, this low-level change >
> >>> poses a number of challenges. For example we have many of places with >
> >>> variations of>
> >>>>
> >>> if(rdfNode.isResource()) { if(rdfNode.isURIResource()) { } else { // >
> >>> Here we now assume it's a blank node, yet this is no longer true // >
> >>> and they node may also be a triple node } } else { // Must be a >
> >>> literal - this hasn't changed }>
> >>>>
> >>> which now need to be changed to handle rdfNode.isStmtResource() too. >
> >>> And it should of course do so in a meaningful way.>
> >>>>
> >>> I guess properly adjusting our code base will take many months, and >
> >>> it will require a lot of testing and iterating.>
> >>>>
> >>> In the meantime, is there a flag that we can set to deactivate RDF* >
> >>> support in the parsers and SPARQL*? The page >
> >>> https://jena.apache.org/documentation/rdfstar/ only states "it is >
> >>> active by default in Fuseki" but doesn't show an API to do the same >
> >>> programmatically.>
> >>>>
> >>> Could you also give some background on the implications on TDB? I >
> >>> guess if such new nodes end up in a database, then this database can >
> >>> no longer work with older Jena versions?>
> >>>>
> >>> Thanks>
> >>> Holger>
> >>>
> >>>
> >>>
>
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
Re: Identify SPARQL query's type
Hi Marco,
I will prepare a presentation of the most important features next week; I can't
say right now which day is best, but maybe we can arrange that on short notice
on the weekend or on Monday via direct mail. As for contributions to Jena
directly, I am already in contact with Andy via some recent JIRA issues and PRs
:)
I also intend to start the discussion on contributing some relevant parts of
our extension project to jena directly. The reason why this did not happen so
far is mainly because it takes significantly more efforts to polish code up for
a such a big community project and ensuring a good level of stability - but
some parts are stable and probably of more general interest :)
Cheers,
Claus
On 19.03.20 10:37, Marco Neumann wrote:
thank you Claus, there is obviously much more in the Jena-extensions
(SmartDataAnalytics / jena-sparql-api).
if you want to contribute your work to the Jena project you will have to
follow up with Andy directly. But I am not sure this is necessary at the
moment since you already provide the code in the public domain conveniently
as an extension / add-on to the Jena project, which I think is great as is
for now. Over time we might want to learn from your work and add aspects to
the overall core Jena project I would think.
It would be great if we could schedule a zoom session in order to give us
an overview of the "SmartDataAnalytics / jena-sparql-api" extensions
could you prepare such a presentation in the coming days?
best,
Marco
On Wed, Mar 18, 2020 at 3:34 PM Claus Stadler <
cstad...@informatik.uni-leipzig.de> wrote:
Hi,
The SparqlStmt API built against jena 3.14.0 is now available on Maven
Central [1] in case one want to give it a try (example in [2]) and give
feedback and whether one thinks it would be a useful contribution to Jena
directly - and what changes would be necessary if so.
org.aksw.jena-sparql-api
jena-sparql-api-stmt
3.14.0-1
[1]
https://search.maven.org/artifact/org.aksw.jena-sparql-api/jena-sparql-api-stmt/3.14.0-1/jar
[2]
https://github.com/SmartDataAnalytics/jena-sparql-api/blob/def0d3bdf0f4396fbf1ef0715f9697e9bb255029/jena-sparql-api-stmt/src/test/java/org/aksw/jena_sparql_api/stmt/TestSparqlStmtUtils.java#L54
Cheers,
Claus
On 18.03.20 16:04, Andy Seaborne wrote:
Note that parsing the string as a query aborts early as soon as it finds
an update keyword so the cost of parsing isn't very large.
Andy
On 18/03/2020 11:58, Marco Neumann wrote:
is there some utility function here in the code base now already to do
this, or do I still need to roll my own here?
On Tue, Jul 30, 2013 at 4:25 PM Andy Seaborne wrote:
On 30/07/13 10:13, Arthur Vaïsse-Lesteven wrote:
Hi,
I would like to know if Jena offers a way to detect the type of an
unknow SPARQL request ?Starting from the query string.
At the moment the only way I succed to code it without "basic parsing"
of the query ( sort of thing I prefer avoid, manually parsing string
with
short function often create errors )
looks like this :
[...]
String queryString = "a query string, may be a select or an
update";
try{
Query select = QueryFactory.create(queryString);
Service.process_select_query(select);//do some work with
the select
}
catch(QueryException e){
UpdateRequest update =
UpdateFactory.create(queryString);
Service.process_update_query(update);//do some work with
the update
}
catch(ProcessException e){
//handle this exception
}
[...]
So is it possible ? Or not ?
Not currently.
You could use a regexp to spot the SELECT/CONSTRUCT/DESCRIBE/ASK
keyword
coming after BASE/PREFIXES/Comments.
Andy
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
Re: Identify SPARQL query's type
My current solution builds on the existing jena infrastructure - but it does
not modify it.
My uses cases for uniform sparql stmt parsing included parsing query strings
against a given prefix mapping and also cleaning queries - so removing unused
prefixes.
I have some test cases in [1] of what it looks like:
PrefixMapping pm = RDFDataMgr.loadModel("rdf-prefixes/wikidata.jsonld");
String queryStr = "INSERT {" +
" ?s wdt:P279 wd:Q7725634 .\n" +
"}\n" +
" WHERE {\n" +
" ?s rdfs:label ?desc \n" +
" FILTER (LANG(?desc) = \"en\").\n" +
" }\n";
// A SparqlStmtParser currently inherits from Function
SparqlStmtParser parser = SparqlStmtParserImpl.create(pm);
SparqlStmt stmt = parser.apply(queryStr); // Probably 'parse' would a nicer
name than the generic apply
SparqlStmtUtils.optimizePrefixes(stmt);
UpdateRequest updateRequest = stmt.getUpdateRequest();
I know its not very well documented, but I hope you can get the gist of the
idea :)
Cheers,
Claus
[1]
https://github.com/SmartDataAnalytics/jena-sparql-api/blob/def0d3bdf0f4396fbf1ef0715f9697e9bb255029/jena-sparql-api-stmt/src/test/java/org/aksw/jena_sparql_api/stmt/TestSparqlStmtUtils.java#L54
On 18.03.20 14:25, Marco Neumann wrote:
thank you Claus and Martynas, both very good ideas here. it's a function we
should move into Jena.
let's look at this in a bit more detail now, I currently envision this to
be a factory method of org.apache.jena.query.Query returning boolean like
.isSelect()
.isAsk()
.isDescribe()
.isUpdate()
Claus your solution would extend the following?
org.apache.jena.sparql.lang.ParserSPARQL11.perform(ParserSPARQL11.java:100)
how is fuseki implementing this during query parsing at the moment?
On Wed, Mar 18, 2020 at 1:00 PM Martynas Jusevičius
wrote:
I always wondered why there is no class hierarchy for SPARQL commands,
similarly to SP vocabulary [1]. Something like
Command
Query
Describe
Construct
Select
Ask
Update
...
So that one could check command type doing instanceof Update or
instance of Select instead of query.isSelectType() etc.
[1] https://github.com/spinrdf/spinrdf/blob/master/etc/sp.ttl
On Wed, Mar 18, 2020 at 12:58 PM Marco Neumann
wrote:
is there some utility function here in the code base now already to do
this, or do I still need to roll my own here?
On Tue, Jul 30, 2013 at 4:25 PM Andy Seaborne wrote:
On 30/07/13 10:13, Arthur Vaïsse-Lesteven wrote:
Hi,
I would like to know if Jena offers a way to detect the type of an
unknow SPARQL request ?Starting from the query string.
At the moment the only way I succed to code it without "basic
parsing"
of the query ( sort of thing I prefer avoid, manually parsing string
with
short function often create errors )
looks like this :
[...]
String queryString = "a query string, may be a select or an
update";
try{
Query select = QueryFactory.create(queryString);
Service.process_select_query(select);//do some work with
the select
}
catch(QueryException e){
UpdateRequest update =
UpdateFactory.create(queryString);
Service.process_update_query(update);//do some work with
the update
}
catch(ProcessException e){
//handle this exception
}
[...]
So is it possible ? Or not ?
Not currently.
You could use a regexp to spot the SELECT/CONSTRUCT/DESCRIBE/ASK
keyword
coming after BASE/PREFIXES/Comments.
Andy
--
---
Marco Neumann
KONA
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
Re: Identify SPARQL query's type
Hi,
I created an abstraction for this awhile ago - essentially there is an
interface 'SparqlStmt' with implementations that wrap an UpdateRequest or a
Query. Correspondingly, there is a SparqlStmtParser interface whose
implementation is makes use of a SparqlQueryParser and SparqlUpdateParser.
If the statement cannot be parsed, it attempts to to get the location of the
parse error (line / col) and decide on the statement type on this basis.
Its on maven central - but I see its not there for jena 3.14.0 but I could do
it today.
https://search.maven.org/artifact/org.aksw.jena-sparql-api/jena-sparql-api-stmt/3.13.1-1/jar
I would also gladly contribute it to jena directly :)
Cheers,
Claus
https://github.com/SmartDataAnalytics/jena-sparql-api/blob/fa5fe33b0e7ac80586cdb3522aa5e0d75718db26/jena-sparql-api-stmt/src/main/java/org/aksw/jena_sparql_api/stmt/SparqlStmtParserImpl.java#L57
On 18.03.20 12:58, Marco Neumann wrote:
is there some utility function here in the code base now already to do
this, or do I still need to roll my own here?
On Tue, Jul 30, 2013 at 4:25 PM Andy Seaborne wrote:
On 30/07/13 10:13, Arthur Vaïsse-Lesteven wrote:
Hi,
I would like to know if Jena offers a way to detect the type of an
unknow SPARQL request ?Starting from the query string.
At the moment the only way I succed to code it without "basic parsing"
of the query ( sort of thing I prefer avoid, manually parsing string with
short function often create errors )
looks like this :
[...]
String queryString = "a query string, may be a select or an
update";
try{
Query select = QueryFactory.create(queryString);
Service.process_select_query(select);//do some work with
the select
}
catch(QueryException e){
UpdateRequest update = UpdateFactory.create(queryString);
Service.process_update_query(update);//do some work with
the update
}
catch(ProcessException e){
//handle this exception
}
[...]
So is it possible ? Or not ?
Not currently.
You could use a regexp to spot the SELECT/CONSTRUCT/DESCRIBE/ASK keyword
coming after BASE/PREFIXES/Comments.
Andy
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
Re: CSV to rdf
Hi all, We have created SparqlIntegrate, examples at: https://github.com/SmartDataAnalytics/SparqlIntegrate/tree/develop/doc It uses Jena's plugin system to register SPARQL functions and property functions(*) for CSV, XML and JSON processing. So its another SPARQL-based approach. (*) https://jena.apache.org/documentation/query/library-propfunc.html Cheers, Claus On 14.02.19 15:19, Martynas Jusevičius wrote: https://github.com/AtomGraph/CSV2RDF Not XSLT but SPARQL-based, yet the transformation concept is similar. I'm the author :) On Thu, Feb 14, 2019 at 2:59 PM elio hbeich wrote: Dear all Do you have any suggestion about tools or XSLT that can transform CSV to RDF Thank you in advance, Elio HBEICH
jena-arq: FROM / FROM NAMED clauses of SPARQL queries over in-memory Dataset are ignored
Hi,
It appears that the FROM / FROM NAMED clauses of SPARQL queries are ignored
when executed over a Dataset.
In the example below, I would expect the first result set to yield the content
of the file, whereas I expect the second one to be empty as the specified named
graph does not exist, yet, I get the exact opposite.
Are there some magic switches or algebra transformations that can be applied
programmatically for changing the behavior?
Similar queries on Virtuoso on http://dbpedia.org/sparql work to my expectation.
Tested with jena-arq 2.13.0 and 3.0.0
A related issue might be this one, but it appears a fix was only provided for
Fuseki: https://issues.apache.org/jira/browse/JENA-1004
Cheers,
Claus
Code:
public class TestDatasetQuery {
@Test
public void test() throws IOException {
Dataset ds = DatasetFactory.createMem();
RDFDataMgr.read(ds, new
ClassPathResource("test-person.nq").getInputStream(), Lang.NQUADS);
String graphName = ds.listNames().next();
Node s =
ds.getNamedModel(graphName).listSubjects().toSet().iterator().next().asNode();
System.out.println("Got subject: " + s + " in graph " + graphName);
{
// Should yield some solutions - but actually doesn't
QueryExecution qe = QueryExecutionFactory.create("SELECT * FROM <" + graphName +
"> { ?s ?p ?o }", ds);
ResultSet rs = qe.execSelect();
System.out.println(ResultSetFormatter.asText(rs));
}
{
// Should not return anything, as the named graph does not exist,
yet, the original data is returned
QueryExecution qe = QueryExecutionFactory.create("SELECT * FROM NAMED
<http://foobar> { Graph ?g { ?s ?p ?o } }", ds);
ResultSet rs = qe.execSelect();
System.out.println(ResultSetFormatter.asText(rs));
}
}
}
File: test-person.nq
<http://ex.org/JohnDoe> <http://ex.org/label> "John
Doe"^^<http://www.w3.org/2001/XMLSchema#string> <http://ex.org/graph/> .
<http://ex.org/JohnDoe> <http://ex.org/age>
"20"^^<http://www.w3.org/2001/XMLSchema#int> <http://ex.org/graph/> .
Output:
Got subject: http://ex.org/JohnDoe in graph http://ex.org/graph/
-
| s | p | o |
=
-
---
| s | p | o
| g |
===
| <http://ex.org/JohnDoe> | <http://ex.org/age> |
"20"^^<http://www.w3.org/2001/XMLSchema#int> | <http://ex.org/graph/> |
| <http://ex.org/JohnDoe> | <http://ex.org/label> | "John Doe"
| <http://ex.org/graph/> |
---
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
Re: Sparql To SQL
There is also Sparqlify[1], which we use for exposing OpenStreetMap as LinkedData in the LinkedGeoData project[2] (and dumpig the RDF for downloads)[3]. Unfortunately, R2RML support not yet totally stable; we wrote our mappings[4] in what we refer to as Sparqlification Mapping Language (SML) [5] (release should be ready soon). In a nutshell, the relation between R2RML to SML is a bit akin to (the SPARQL elements of) SPIN to SPARQL, for a pretty comprehensive comparision of examples (the R2RML test suite) see [6]. Cheers, Claus [1] https://github.com/AKSW/Sparqlify (Instructions for installing Sparqlify from the debian package are included there) [2] LinkedGeoData: http://linkedgeodata.org [3] http://downloads.linkedgeodata.org/releases [4] https://github.com/GeoKnow/LinkedGeoData/blob/master/linkedgeodata-core/src/main/resources/org/aksw/linkedgeodata/sml/LinkedGeoData-Triplify-IndividualViews.sml [5] http://sml.aksw.org [6] http://sml.aksw.org/comparison/sml-r2rml-loc-table.html On 31.03.2014 01:29, Martynas Jusevičius wrote: There are also commercial options, e.g. this: http://www.revelytix.com/content/spyder On Sun, Mar 30, 2014 at 10:15 PM, Kamalraj Jairam kjai...@semanticsoftware.com.au wrote: Hello Paul, These are the informtion i have 1) R2RML mapping for existing DB 2) I have some fedreated queries which hit the triple store containg the data which has been loaded from the DB The Loading data from DB (100 tables, millions of rows) to TS takes a long time. I need a framework to convert Sparql to SQL which will hit the table and return RDF result set. D2RQ is in version .81 and hasn't changed much. Not sure whether D2RQ is the right approach. Thanks Kamalraj -- Kjairam Sent with Airmail On 31 March 2014 at 6:59:20 am, Paul Tyson (phty...@sbcglobal.netmailto:phty...@sbcglobal.net) wrote: On Sun, 2014-03-30 at 09:37 +, Kamalraj Jairam wrote: Hello All, Whats the best way to convert sparql to SQL using R2RML mappings and convert resultset from DB to RDF? What are the givens? Do you have existing SPARQL text written against some RDF produced by some existing R2RML mappings? Or do you have some SPARQL and some SQL and you want to fill in the R2RML and produce some RDF? In any case, it is an interesting scenario that will arise more often as companies expand their use of RDF while relying mostly on SQL. There is a higher abstraction that should be explored and possibly exploited to provide a general pattern for working through these situations. Since SQL, SPARQL, and R2RML are rule languages compatible with relational algebra (RA), it should be possible to derive a common set of RA predicates and classes to create an RDF vocabulary. This vocabulary can then be used to write queries as production rules in a generic standard rule language, such as RIF (Rule Interchange Format). The RIF source can be translated to SQL, SPARQL, or R2RML for execution in the target system. Going from RIF to SQL, SPARQL, or R2RML is always going to be easier than starting from SQL or SPARQL and going to some other format. Theoretically you should be able to partially translate R2RML to RIF automatically (SQL embedded in the R2RML will still be opaque). But I don't know what tools could be used to translate SQL and SPARQL texts to generic production rules using an RA vocabulary. The ultimate payoff from this approach is that it will be possible to link all of your data relations and operations with meaningful business terminology and processes. It will enable greater visibility and control of all data operations, and put important elements of business logic in transparent rules (e.g. RIF) instead of arcane notations such as SQL SPARQL (or worse, procedural code). Regards, --Paul -- Dipl. Inf. Claus Stadler Department of Computer Science, University of Leipzig Research Group: http://aksw.org/ Workpage WebID: http://aksw.org/ClausStadler Phone: +49 341 97-32260
Re: How can I implement pagination for ResultSet
Hi,
For the pagination issue combined with client side caching (and adding
delay for not overloading the endpoint), I have written this utility lib
some time ago:
https://github.com/AKSW/jena-sparql-api
Its currently for the prior Jena 2.10.0, but will be upgraded soon.
As for
2) Get the size of ResultSet. but there are no way to get the total
number that ResultSet contains.
A cheap way of getting the count is doing a query for it with Select
(Count(*) As ?c) { { your original query here} }. Although I prefer
modifying the projection in Jena's Query object as I dislike string hacks.
Best,
Claus
On 22.10.2013 19:21, Wang Dongsheng wrote:
By the way, I want to ask you two questions accordingly,
For 1), Can I get the total number first? cause it's better to
calculate how much pages there are in advance.
For 2), If the resultSet is very Large, will the transferring to List
being broken up easily?
On Tue, Oct 22, 2013 at 6:31 PM, Wang Dongsheng dswang2...@gmail.com wrote:
Hi Samuel,
Thanks a lot, It's very cool~ :)
Sincere~
Wang
On Tue, Oct 22, 2013 at 4:22 PM, Samuel Croset samuel.cro...@gmail.com wrote:
Hi,
For 1) you can use the OFFSET and LIMIT constructs
For 2) You can use: ResultSetFormatter.toList()
See this answer
http://answers.semanticweb.com/questions/9456/jena-pagination-for-sparql for
more details.
Cheers,
Samuel
On Tue, Oct 22, 2013 at 8:24 AM, Wang Dongsheng dswang2...@gmail.comwrote:
Hi, all
I want to implement pagination for ResultSet of Sparql.
I guess there are generally two ways:
1, Through a specified SPARQL format, but I dont know how to write the
query,
2. Get the size of ResultSet. but there are no way to get the total
number that ResultSet contains.
I prefer to implement the second way, But Doc of API seems unavailable.
Any one tried this kind of effort? Or it was not suitable to paginate
the result?
Thank in advance~
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
Re: Future of Jena SDB
Hi, Just a quick note, as I am the developer of Sparqlify[1], which pretty much is a general SQL-to-RDF mapping layer (well, or at least SPARQL-SQL rewriter) based on Jena (it also has some dependencies to SDB). From my experience, although I had and still have some dependencies to SDB, but I had to e.g. duplicate the SqlExpr hierachy (e.g. [2]) because I needed each SqlExpr to provide its datatype). The old master branch of Sparqlify already had initial support for rewriting spatial predicates to SQL (only ST_Intersects and ST_DWithin), but we are currently enhancing this system to allow one to essentially expose any (or at least most) SQL functions as a SPARQL one. [1] https://github.com/AKSW/Sparqlify [2] https://github.com/AKSW/Sparqlify/tree/master/sparqlify-core/src/main/java/org/aksw/sparqlify/algebra/sql/exprs2 Cheers, Claus On 06/07/2013 11:54 AM, Olivier Rossel wrote: Could SDB be useful when dealing with GeoSPARQL and your backend is (something like) Postgresql+Postgis? (just a question, this is not one of my needs at the moment). On Fri, Jun 7, 2013 at 11:29 AM, Andy Seaborne a...@apache.org wrote: SDB is a Jena storage module that uses SQL databases for RDF storage. See [1] for documentation. It uses a custom database schema to store RDF; it is not a general SQL-to-RDF mapping layer. The supported databases are: Oracle, Microsoft SQL Server, DB2, PostgreSQL, MySQL, Apache Derby, H2, HSQLDB. Only Derby and HSQLDB are tested in the development build process. Both Oracle and IBM corporations provide commercial RDF solutions using Jena that are completely unrelated to SDB. TDB is faster, more scalable and better supported than SDB but there can be reasons why an SQL-backed solution is appropriate. There is no active development or maintenance of SDB from within the committer team; no committers use SDB and it imposes a cost to the team to generate separate releases. We're not receiving patches contributed to JIRA items for bugs. We are proposing: 1/ moving it into the main build so it will be part of the main distribution with limited testing. 2/ marking it as under review / maintenance only. It will not be treated as something that can block a release, nor for any significant length of time, stop development builds. It may be pulled from the main build, and from a release, at very short notice. If moved out, the source code will still be available but no binaries (releases or development builds) will be produced. What would change SDB's status is care and attention. There are ways to enhance it, for example, pushing the work of filters into the SQL database, where possible, to improve query performance. Andy [1] http://jena.apache.org/**documentation/sdb/index.htmlhttp://jena.apache.org/documentation/sdb/index.html -- Dipl. Inf. Claus Stadler Department of Computer Science, University of Leipzig Research Group: http://aksw.org/ Workpage WebID: http://aksw.org/ClausStadler Phone: +49 341 97-32260
Request for a QueryExecutionFactory interface
Hi,
Would it be possible to add a QueryExecutionFactory (QEF) *interface* to
Jena?
The com.hp.hpl.jena.query.QueryExecutionFacotry has lots of static
factory methods, but I guess it would be very useful if Jena itself
provided such an interface (either different package, different name or
both) because
then implementations based on Jena could rely on such interface (see
below and [1]) in a (quasi) standard way, and other projects could
provide fancy implementations.
public interface QueryExecutionFactory
extends QueryExecutionFactoryString, QueryExecutionFactoryQuery
{ /** * Some Id identifying the SPARQL service, such as a name given to
a jena Model or the URL of a remote service */
String getId(); /** * Some string identifying the state of this
execution factory, such as the selected graphs, or for query federation
the configured endpoints and their respective graphs. * Used for caching */
String getState();
}
The reason I ask this, is because I created [2], which uses this
architecture to transparently add delay, caching and pagination to a QEF
- i.e. you could just pose a usual SPARQL query to DBpedia, and [2] will
take care of retrieving the *complete* result, thereby caching each page
so that one can resume pagination from cache should something go wrong.
But for example, someone might provide a parallel pagination component,
or some query federation system, such as FedX could be wrapped with such
interface as well, and application developers would not have to rely on
a specific implementation.
Cheers,
Claus
[1]
https://github.com/AKSW/jena-sparql-api/blob/master/jena-sparql-api-core/src/main/java/org/aksw/jena_sparql_api/core/QueryExecutionFactory.java
[2] https://github.com/AKSW/jena-sparql-api
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
