The central notion of RDF is the IRI, or URI, which serves as the globally unique label of named nodes. The subject and predicate of a triple are always IRI's and the object may be an IRI or any other XML Schema scalar data type. In any case, an IRI is always distinct from any instance of any other data type.

Virtuoso supports a native IRI_ID data type, internally an unsigned 32 bit or unsigned 64 bit integer value. Small databases can use 32 bit values but if database becomes big then the administrator should execute DB.DBA.RDF_64BIT_UPGRADE () procedure that will switch to 64-bit values. This procedure takes time so if it is known in advance that the database will grow to billions of nodes then it could be convenient to upgrade it while it is empty. An IRI_ID is never equal to any instance of any other type.

Thus, the object column of a table storing triples can be declared as ANY and IRI values will be distinguishable without recourse to any extra flag and IRI's will naturally occupy their own contiguous segment in the ANY type collation sequence. Indices can be defined over such columns. An IRI_ID is never automatically cast into any other type nor any other type into IRI_ID.

The functions iri_id_num (in i IRI_ID) and iri_id_from_num (in n INT) convert between signed integers and IRI_ID's. The function isiri_id (in i any) returns nonzero if the argument is of type IRI_ID, zero otherwise.

The syntax for an IRI_ID literal is #i<NNN> or #ib<NNN> , where <NNN> is up to 20 decimal digits. #i12345 is equal to iri_id_from_num (12345) and #ib12345 is equal to iri_id_from_num (12345) + min_64bit_bnode_iri_id () .

When received by a SQL client application, the ODBC driver or interactive SQL will bind an IRI_ID to a character buffer, producing the #i<NNN> syntax. When passing IRI_ID's from a client, one can pass an integer and use the iri_id_from_num () function in the statement to convert server side. A SQL client will normally not be exposed to IRI_ID's since the SPARQL implementation returns IRI's in their text form, not as internal id's. These will however be seen if reading the internal tables directly.

	Note
	Nobody, even DBA, should write directly to internal RDF tables, because some data from that tables are cached in a special way and cache is not automatically updated when content of tables has changed.

Example

The following example demonstrates IRI type usage as Virtuoso PL function parameter:

SQL>create procedure vs_property_label (in _uri varchar)
  {
    declare res varchar;
    result_names (res);
    for (sparql define input:storage "" select distinct ?graph_rvr_fixed where { graph `iri(?:_uri)` { ?qmv virtrdf:qmGraphRange-rvrFixedValue ?graph_rvr_fixed}})
    do {
      result ("graph_rvr_fixed");
    }
  }
;
Done. -- 0 msec.

SQL>select vs_property_label('http://www.openlinksw.com/schemas/virtrdf#');
res
VARCHAR
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