16.1.4. Short, Long and SQL Values

When processing an O, the SPARQL implementation may have it in one of three internal formats, called "valmodes". The below cases apply for strings:

The short format is the format where an O is stored in RDF_QUAD.

The long value is similar to short one but an rdf_box object, that consists of six fields:

  • short integer id of type referencing RDT_TWOBYTE, 257 if the type is not specified,

  • the string as inlined in O or as stored in RO_VAL or RO_LONG,

  • the RO_ID if the string is from RDF_OBJ (otherwise zero),

  • the short integer id of language referencing RL_TWOBYTE, 257 if the language is not specified,

  • flag whether the stored string value is complete or it is only the beginning that is inlined in O.

The SQL value is the string as a narrow string representing the UTF8 encoding of the value, stripped of data type and language tag.

The SQL form of an IRI is the string. The long and short forms are the IRI_ID referencing RU_IRI_ID of RDF_URL.

For all non-string, non-IRI types, the short, long and SQL values are the same SQL scalar of the appropriate native SQL type. A SQL host variable meant to receive an O should be of the ANY type.

The SPARQL implementation will usually translate results to the SQL format before returning them. Internally, it uses the shortest possible form suited to the operation. For equalities and joining, the short form is always good. For range comparisons, the long form is needed etc. For arithmetic, all three forms will do since the arguments are expected to be numbers which are stored as their binary selves in O, thus the O column unaltered and uncast will do as an argument of arithmetic or numeric comparison with, say, SQL literal constants.