Question

I have a problem about registering namespace in AllegroGraph.

My Java code (program 1):

AllegroGraphConnection agc = new AllegroGraphConnection();
 agc.enable();

 AllegroGraph ag = agc.create("test", AGPaths.TRIPLE_STORES);

 AGUtils.printStringArray("AG Namespaces (initially):", ag.getNamespaces());

 ag.registerNamespace("foaf","http://xmlns.com/foaf/0.1/");
 ag.registerNamespace("dc", "http://purl.org/dc/elements/1.1/");
 ag.registerNamespace("dct", "http://purl.org/dc/terms/");
 ag.registerNamespace("exif","http://www.w3.org/2003/12/exif/ns#");
 ag.registerNamespace("prf", "http://www.openmobilealliance.org/tech/profiles/UAPROF/ccppschema-2007511#");

 AGUtils.printStringArray("AG Namespaces (registed):", ag.getNamespaces());

Run, And the result(program 1):

AG Namespaces (initially):
0: rdf
1: http://www.w3.org/1999/02/22-rdf-syntax-ns#
2: rdfs
3: http://www.w3.org/2000/01/rdf-schema#
4: owl
5: http://www.w3.org/2002/07/owl#

AG Namespaces (registered):

  0: rdf
  1: http://www.w3.org/1999/02/22-rdf-syntax-ns#
  2: rdfs
  3: http://www.w3.org/2000/01/rdf-schema#
  4: owl
  5: http://www.w3.org/2002/07/owl#
  6: foaf
  7: http://xmlns.com/foaf/0.1/
  8: dc
  9: http://purl.org/dc/elements/1.1/
  10: dct
  11: http://purl.org/dc/terms/
  12: exif
  13: http://www.w3.org/2003/12/exif/ns#
  14: prf
  15: http://www.openmobilealliance.org/tech/profiles/UAPROF/ccppschema-2007511#

Then, my Java code (program 2):

AllegroGraphConnection agc = new AllegroGraphConnection();
 agc.enable();

 AllegroGraph ag = agc.open("test", AGPaths.TRIPLE_STORES);

 AGUtils.printStringArray("AG Namespaces (registed):", ag.getNamespaces());

Run, and the result(program 2):

AG Namespaces (registered):

 0: rdf
  1: http://www.w3.org/1999/02/22-rdf-syntax-ns#
  2: rdfs
  3: http://www.w3.org/2000/01/rdf-schema#
  4: owl
  5: http://www.w3.org/2002/07/owl#

In program 1, I create a AllegroGraph which name is "test", and I registered the other 5 namespaces(foaf, dc, dct, exif, prf); in program 2, I open the created AllegroGraph, but its namespace has only 3: rdf, rdfs, owl, the other 5 namespaces which is registered in program 1 is missing.

My question is:

Why the other 5 namespaces missed?
How can I keep the 5 registered namespaces in created AllegroGraph? (When I open the created AllegroGraph, I need not to register namespaces again.)

And in my program, after registered all the nameSpace, I added the following code:

ag.closeTripleStore();

and it is unuseful:(

Answer 1

In short, AllegroGraph does not persist namespace registration in the triple-store. Namespaces are syntactic sugar that exist to make it easier to read and write long URIs. Even though there are many commonly used abbreviations (rdf, owl, foaf, dc, ...), each person can make up their own and use them as they see fit. If AllegroGraph persisted the namespace abbreviations, then the store would carry someone s personal abbreviations with it which could cause confusion if someone else opened the store.

In short, if you want to use namespaces, you should set up your code to re-register them on start up. Also, note that the namespace abbreviations are global to the running instance, not to a particular triple-store.

HTH

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