Hi Claude, thanks for the explanation: from the dataset-as-quads perspective it does indeed sound logical that empty graphs do not exist.
Regarding your second answer, I've added some additional information below (i.e. these can also be found on the github repo: https://github.com/barrynl/jena-example). The SPARQL is executed on the dataset described by the conf.ttl below. It does not have a GRAPH specified in the query and it would indeed go into the default graph, which is a UnionModel of the two in-memory named graphs. Of which the rootGraph should store this new data. The details of how I inspect the different graphs can be found in the Java code in the link above. If you run this example and inspect the output log and 'dataset' variable (and the inner models and graphs) with a debugger, the data sometimes shows up and sometimes doesn't. I am trying to understand why... Any more ideas? Regards, Barry ---------------------------------------- SPARQL ---------------------------------------- INSERT DATA { :test rdf:type pizza:Pizza . :test pizza:hasCountryOfOrigin <http://192.168.99.100/pizza/Italy> . :test pizza:hasBase <http://192.168.99.100/pizza/23_base> . :test pizza:hasSpiciness <http://192.168.99.100/pizza/23_flauw> . :test pizza:hasTopping :18-Tomaat . :test pizza:hasTopping :18-mozzerella . :test pizza:hasTopping :18-rundergehakt . } ---------------------------------------- conf.ttl ---------------------------------------- @prefix : <#> . @prefix fuseki: <http://jena.apache.org/fuseki#<http://jena.apache.org/fuseki>> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#<http://www.w3.org/1999/02/22-rdf-syntax-ns>> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#<http://www.w3.org/2000/01/rdf-schema>> . @prefix ja: <http://jena.hpl.hp.com/2005/11/Assembler#<http://jena.hpl.hp.com/2005/11/Assembler>> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#<http://www.w3.org/2001/XMLSchema>> . :service1 rdf:type fuseki:Service ; fuseki:name "test" ; fuseki:serviceQuery "query" ; # SPARQL query service fuseki:serviceUpdate "update" ; fuseki:serviceUpload "upload" ; # Non-SPARQL upload service fuseki:serviceReadWriteGraphStore "data" ; # SPARQL Graph store protocol (read and write) # A separate read-only graph store endpoint: fuseki:serviceReadGraphStore "get" ; # SPARQL Graph store protocol (read only) fuseki:dataset :dataset . :dataset rdf:type ja:RDFDataset ; ja:defaultGraph :unionModel ; ja:namedGraph [ ja:graphName <https://www.tno.nl/agrifood/graph/pizza/data> ; ja:graph :itemGraph ] ; ja:namedGraph [ ja:graphName <https://www.tno.nl/agrifood/graph/pizza/onto> ; ja:graph :ontoGraph ] . :unionModel rdf:type ja:UnionModel ; ja:rootModel :itemGraph ; ja:subModel :ontoGraph . :itemGraph rdf:type ja:MemoryModel ; ja:content [ ja:externalContent <file:src/main/resources/dummy1.ttl> ] . :ontoGraph rdf:type ja:MemoryModel ; ja:content [ ja:externalContent <file:src/main/resources/dummy2.ttl> ] . -----Original Message----- From: Claude Warren <cla...@xenei.com> Sent: donderdag 26 september 2019 12:10 To: users@jena.apache.org Subject: Re: [UnionModel] question about unexpected behaviour Empty graphs in Fuseki simply don't exist. They no more exist than a predicate that has not been used. Named graphs only come into existence when there is at least one triple added to it. If you think about datasets as collections of quads (<g> <s> <p> <o>) then you can see that the dataset can only locate graphs that have data. The only other option is that an infinite number of graphs exist, in which case listing all the graphs would be impossible. I am sure there is a deep philosophical discussion here but the Jena rule is that if the graph does not have data it does not exist. As for your second question, you did not give an example of how you inserted the data. If you did not provide a graph name to insert into then the data would go into the default graph named "urn:x-arq:DefaultGraph" (defined in org.apache.jena.sparql.core.Quad.defaultGraphIRI). If you did provide the graph name then the data would be inserted into that graph as your debugging shows. When you say it does not exist in the graph are you referring to on disk? How did you write the data back out? The UnionModel depends on the underlying models to preserve their data. If those models are in-memory models then they will not be written back to disk, if they are TDB models (or other similar auto storing models) then they should be written back to the underlying storage. This assumes that all transactions and other issues are correctly handled. Claude On Thu, Sep 26, 2019 at 10:05 AM Nouwt, B. (Barry) <barry.no...@tno.nl.invalid> wrote: > Hi all, > > I am trying to get the Apache Jena UnionModel working for my scenario, > but I keep encountering unexpected behavior. I've set up a minimal, > free-standing example on github in this repository (clone the git > repo, configure Maven in your IDE and execute the main() method, I.e. > it probably does not run from the .jar): > > https://github.com/barrynl/jena-example > > > > I have two questions related to this example: > > My first question is related to empty graphs in Jena Fuseki. If I load > the conf.ttl (from the git repo above) at startup in Apache Jena > Fuseki without the dummy data in the two named graphs, the two graphs > seem to disappear (I think this does not happen in my Java Example). I > read somewhere that empty graphs are automatically deleted in Fuseki > to prevent old graphs from showing up in the Fuseki interface. For my > use case I would like to configure two (possibly empty at first) named > graphs via a conf.ttl and be able to store data in them afterwards. Is this > possible? > > My second question is about the demonstraded behaviour of the Java > example in the git repository above. I load a dataset with a > UnionModel from a conf.ttl file and insert new data in it via SPARQL. > Although the new data shows up in the select query, it does not show > up in either of the two names graphs the UnionModel consists of. My > question is: where is this data stored if not in one of the names > graphs? (If I inspect the UnionModel via a debugger, the inserted data > DOES show up in the correct named graph) > > Hopefully someone can shed some light on this behaviour. Thanks in advance! > > Regards, Barry > This message may contain information that is not intended for you. If > you are not the addressee or if this message was sent to you by > mistake, you are requested to inform the sender and delete the > message. TNO accepts no liability for the content of this e-mail, for > the manner in which you use it and for damage of any kind resulting > from the risks inherent to the electronic transmission of messages. > -- I like: Like Like - The likeliest place on the web <http://like-like.xenei.com> LinkedIn: http://www.linkedin.com/in/claudewarren
