The SPARQL specification does not define the precise output of DESCRIBE, so different applications may need different results for the same subject. Some applications need quick generation of short and incomplete results whereas others may need detailed reports composed from multiple sources.

The supported option values for sql:describe-mode are:

  • (default)

    -- for subject-predicate-object triples of given IRI as subject plus subject-predicate-object triples of given IRI as object. No "sql:describe-mode" or define sql:describe-mode "" will set default.

  • SPO

    -- for subject-predicate-object triples of given IRI as subject;

  • CBD

    -- for concise bound description of given subject (i.e., SPO + CBD of each blank node object found by SPO, recursively);

  • OBJCBD

    -- like CBD but traverses from objects to subjects, not from subjects to objects;

  • In addition, user may write his/her own "postporocessing" function that will get the result of describe, lists of "good" and "bad" graphs, name of storage, options and alter it in any way he/she wishes. The notation is e.g. define sql:describe-mode "SPO+XYZ", meaning SPO describe and call DB.DBA.SPARQL_DESC_POSTPROC_XYZ on top of it. See below example usage.

If define sql:describe-mode "xxx" is specified then the generated SQL code will use the procedures named:

DB.DBA.SPARQL_DESC_DICT_xxx (in subj_dict any, in consts any, in graphs
any, in storage_name any, in options any)

and

DB.DBA.SPARQL_DESC_DICT_xxx_PHYSICAL (in subj_dict any, in consts any,
in graphs any, in storage_name any, in options any)

In a new blank database, only two such pairs of procedures are created. Procedures DB.DBA.SPARQL_DESC_DICT_SPO and DB.DBA.SPARQL_DESC_DICT_SPO_PHYSICAL are for sql:describe-mode "SPO" . This pair of procedures searches for all triples where the input IRIs are used as subjects; they are faster than the default routine which searches for all triples where the input IRIs are used as subjects or objects. Similarly, DB.DBA.SPARQL_DESC_DICT_CBD and DB.DBA.SPARQL_DESC_DICT_CBD_PHYSICAL are for sql:describe-mode "CBD" . CBD stands for Concise Bounded Description of given subject (i.e., SPO + CBD of each blank node object found by SPO, recursively).

In each pair, both procedures have the same semantics but the second one is used if and only if the SPARQL compiler can prove that all subjects to process are from physical storage (DB.DBA.RDF_QUAD) . Thus the second procedure will not search for subjects in Linked Data Views.

Each procedure should return a dictionary with triples as keys and integer 1 as values. So the dictionary is filled by calls like:

dict_put (resulting_dict,
          vector (subj_iri_id, pred_iri_id, obj_iri_id_or_rdf_box),
          1);

Procedure arguments are as follows:

  • subj_dict

    - a dictionary whose keys are IRI IDs and maybe values of other types, esp. RDF boxes. Keys are subjects to be described, so values other than IRI IDs should usually be ignored. Values should be ignored.

  • consts

    - a vector of IRI IDs and values of other types. The items contained in the vector are subjects to be described, as with the keys of subj_dict.

  • graphs

    - a vector of IRI IDs of graphs that can be used for DESCRIBE. The vector may contain garbage, like in the two previous cases. A NULL can be passed instead of a vector indicating that the source graphs are not specified in the source query.

  • storage_name

    - the value of "define input:storage" from the original SPARQL query, NULL if missing.

  • options

    - reserved for future use and can be ignored.

One should grant execute permission on both procedures to SPARQL_SELECT before referring to them in SPARQL.

Assume the following statements are executed:

__rdf_set_bnode_t_treshold();
SET blobs ON;
SET echo ON;

SPARQL PREFIX xmp: <http://example.com/xmp/>
CLEAR GRAPH xmp:good1;

SPARQL PREFIX xmp: <http://example.com/xmp/>
CLEAR GRAPH xmp:good2;

SPARQL PREFIX xmp: <http://example.com/xmp/>
CLEAR GRAPH xmp:bad1;

SPARQL PREFIX xmp: <http://example.com/xmp/>
CLEAR GRAPH xmp:bad2;

SPARQL PREFIX xmp: <http://example.com/xmp/>
INSERT IN xmp:good1
  {
    xmp:Top1 xmp:item xmp:TheSubject .
    xmp:TheSubject xmp:details
            xmp:ChildObject ,
            ( xmp:car xmp:cadr xmp:caddr ) .
  };

SPARQL PREFIX xmp: <http://example.com/xmp/>
INSERT IN xmp:good2
  {
    xmp:Top2 xmp:items [ rdf:_1 xmp:TheSubject ; rdf:_2 xmp:OtherSubject ] .
  };
SPARQL
DEFINE output:format "NICE_TTL"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject FROM xmp:good1 FROM xmp:good2;

fmtaggret-NICE_TTL
LONG VARCHAR
 @prefix ns0: <http://example.com/xmp/> .
 @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
 ns0:Top1 ns0:item ns0:TheSubject .
 ns0:TheSubject ns0:details ns0:ChildObject , [ ] .
 _:vb78520012 rdf:_1 ns0:TheSubject .

Example 1

SPARQL
DEFINE output:format "NICE_TTL"
DEFINE sql:describe-mode "SPO"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject FROM xmp:good1 FROM xmp:good2;

fmtaggret-NICE_TTL
LONG VARCHAR
 @prefix ns0: <http://example.com/xmp/> .
 ns0:TheSubject ns0:details ns0:ChildObject , [ ] .

Example 2

SQL>set blobs on;
SQL>SPARQL
define sql:describe-mode "SPO"
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX sioct: <http://rdfs.org/sioc/types#>

DESCRIBE ?forum
FROM <http://demo.openlinksw.com/dataspace>
WHERE {
  ?forum rdf:type sioct:Weblog .
}
LIMIT 1;

callret-0
LONG VARCHAR
_______________________________________________________________________________

<http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://rdfs.org/sioc/types#Weblog> ,
                <http://atomowl.org/ontologies/atomrdf#Feed> ;
        <http://rdfs.org/sioc/ns#description> "XML templates demo's Weblog" ;
        <http://rdfs.org/sioc/ns#has_space> <http://demo.openlinksw.com/dataspace/bloguser/space#this> ;
        <http://rdfs.org/sioc/ns#container_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/20> ,
                <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/21> ;
        <http://rdfs.org/sioc/ns#id> "bloguser_blog" ;
        <http://xmlns.com/foaf/0.1/maker> <http://demo.openlinksw.com/dataspace/person/bloguser#this> ;
        <http://rdfs.org/sioc/ns#link> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> ;
        <http://atomowl.org/ontologies/atomrdf#entry> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/20> ,
                <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/21> ;
        <http://atomowl.org/ontologies/atomrdf#contains> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/21> ,
                <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/20> ;
        <http://atomowl.org/ontologies/atomrdf#title> "bloguser_blog" ;
        <http://www.w3.org/2000/01/rdf-schema#label> "XML templates demo's Weblog" ;
        <http://rdfs.org/sioc/ns#scope_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog#owner> ;
        <http://rdfs.org/sioc/ns#has_owner> <http://demo.openlinksw.com/dataspace/bloguser#this> ;
        <http://www.w3.org/2000/01/rdf-schema#isDefinedBy> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/sioc.rdf> ;
        <http://purl.org/dc/elements/1.1/identifier> "62"^^<http://www.w3.org/2001/XMLSchema#integer> ;
        <http://rdfs.org/sioc/services#has_service> <http://demo.openlinksw.com/RPC2> ,
                <http://demo.openlinksw.com/mt-tb> ,
                <http://demo.openlinksw.com/Atom/bloguser-blog-0> ,
                <http://demo.openlinksw.com/GData/bloguser-blog-0> .
<http://demo.openlinksw.com/RPC2> <http://rdfs.org/sioc/services#service_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/mt-tb> <http://rdfs.org/sioc/services#service_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog#owner> <http://rdfs.org/sioc/ns#has_scope> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/20> <http://rdfs.org/sioc/ns#has_container> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> ;
        <http://atomowl.org/ontologies/atomrdf#source> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog/21> <http://rdfs.org/sioc/ns#has_container> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> ;
        <http://atomowl.org/ontologies/atomrdf#source> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/dataspace/bloguser#this> <http://rdfs.org/sioc/ns#owner_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/dataspace/bloguser/space#this> <http://rdfs.org/sioc/ns#space_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/dataspace/person/bloguser#this> <http://xmlns.com/foaf/0.1/made> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/Atom/bloguser-blog-0> <http://rdfs.org/sioc/services#service_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .
<http://demo.openlinksw.com/GData/bloguser-blog-0> <http://rdfs.org/sioc/services#service_of> <http://demo.openlinksw.com/dataspace/bloguser/weblog/bloguser_blog> .

1 Rows. -- 240 msec.

Example 1

SPARQL
DEFINE output:format "NICE_TTL"
DEFINE sql:describe-mode "CBD"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject FROM xmp:good1 FROM xmp:good2;

Query result:
fmtaggret-NICE_TTL
LONG VARCHAR
 @prefix ns0: <http://example.com/xmp/> .
 @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
 ns0:TheSubject ns0:details ns0:ChildObject , ( ns0:car ns0:cadr ns0:caddr ) .

Example 2

SPARQL
DEFINE output:format "NICE_TTL"
DEFINE sql:describe-mode "CBD"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject  xmp:good1 from xmp:good2;

Example 2

SQL>SPARQL
DEFINE sql:describe-mode "CBD"
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
DESCRIBE ?friend
WHERE
  {
    ?s foaf:knows ?friend  .
    ?friend foaf:nick ?nick.
    filter (?s=<http://www.advogato.org/person/rmorgan/foaf.rdf#me>)
}
;

@prefix rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix ns1:    <http://www.advogato.org/person/chrisd/foaf.rdf#> .
@prefix foaf:   <http://xmlns.com/foaf/0.1/> .
ns1:me  rdf:type        foaf:Person .
@prefix rdfs:   <http://www.w3.org/2000/01/rdf-schema#> .
ns1:me  rdfs:seeAlso    <http://www.advogato.org/person/chrisd/foaf.rdf> ;
        foaf:name       "Chris DiBona" ;
        foaf:nick       "chrisd" ;
        foaf:homepage   <http://www.dibona.com> ;
        foaf:mbox_sha1sum       "e8231d19ac0d11ccbdc565485054461e5d71f0d3" .
@prefix ns4:    <http://www.advogato.org/person/schoen/foaf.rdf#> .
ns1:me  foaf:knows      ns4:me .
@prefix ns5:    <http://www.advogato.org/person/jpick/foaf.rdf#> .
ns1:me  foaf:knows      ns5:me .
@prefix ns6:    <http://www.advogato.org/person/benson/foaf.rdf#> .
ns1:me  foaf:knows      ns6:me .
@prefix ns7:    <http://www.advogato.org/person/conrad/foaf.rdf#> .
ns1:me  foaf:knows      ns7:me .
@prefix ns8:    <http://www.advogato.org/person/starshine/foaf.rdf#> .
ns1:me  foaf:knows      ns8:me .
@prefix ns9:    <http://www.advogato.org/person/chip/foaf.rdf#> .
ns1:me  foaf:knows      ns9:me .
@prefix ns10:   <http://www.advogato.org/person/crackmonkey/foaf.rdf#> .
.....

Example 1

SPARQL
DEFINE output:format "NICE_TTL"
DEFINE sql:describe-mode "OBJCBD"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject FROM xmp:good1 FROM xmp:good2;

Query result:
fmtaggret-NICE_TTL
LONG VARCHAR
 @prefix ns0: <http://example.com/xmp/> .
 @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
 ns0:Top1 ns0:item ns0:TheSubject .
 ns0:Top2 ns0:items [ rdf:_1 ns0:TheSubject ] .
create function DB.DBA.SPARQL_DESC_POSTPROC_SOURCES (inout triples any array, in good_graphs any array, in bad_graphs any array, in storage varchar, in opts any array)
{
  declare triple, val, so_dict, so_lst, addon_dict, dlst any;
  dbg_obj_princ ('DB.DBA.SPARQL_DESC_POSTPROC_SOURCES (', triples, good_graphs, bad_graphs, storage, opts, ')');
  so_dict := dict_new (dict_size (triples));
  dict_iter_rewind (triples);
  while (dict_iter_next (triples, triple, val))
    {
      declare v any;
      v := triple[0];
      dict_put (so_dict, iri_to_id_nosignal (v), 1);
      v := triple[2];
      if (isiri_id (v) or (isstring (v) and box_tag (v) = 1))
        dict_put (so_dict, iri_to_id_nosignal (v), 1);
    }
  so_lst := dict_list_keys (so_dict, 1);
  foreach (any s_itm in so_lst) do
    {
      for (sparql select distinct ?g where { graph ?g {{ `iri(?:s_itm)` ?p ?o } union { ?s ?p  `iri(?:s_itm)` }} filter (<LONG::bif:position>(?g, ?:good_graphs))}) do
        dict_put (triples, vector (s_itm, iri_to_id('Source'), "g"), 1);
    }
  return triples;
}
;

SPARQL
DEFINE output:format "NICE_TTL"
DEFINE sql:describe-mode "CBD+SOURCES"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject FROM xmp:good1 FROM xmp:good2;

SELECT sparql_to_sql_text ('
DEFINE output:format "NICE_TTL"
DEFINE sql:describe-mode "CBD+SOURCES"
PREFIX xmp: <http://example.com/xmp/>
DESCRIBE xmp:TheSubject FROM xmp:good1 FROM xmp:good2') as x long varchar;