Querying

Querying — RDF query languages and execution.

Synopsis

typedef             librdf_query;
typedef             librdf_query_factory;
void                librdf_query_register_factory       (librdf_world *world,
                                                         const char *name,
                                                         const unsigned char *uri_string,
                                                         void (*factory) (librdf_query_factory*));
const raptor_syntax_description * librdf_query_language_get_description
                                                        (librdf_world *world,
                                                         unsigned int counter);
int                 librdf_query_languages_enumerate    (librdf_world *world,
                                                         const unsigned int counter,
                                                         const char **name,
                                                         const unsigned char **uri_string);
librdf_query *      librdf_new_query                    (librdf_world *world,
                                                         const char *name,
                                                         librdf_uri *uri,
                                                         const unsigned char *query_string,
                                                         librdf_uri *base_uri);
librdf_query *      librdf_new_query_from_query         (librdf_query *old_query);
librdf_query *      librdf_new_query_from_factory       (librdf_world *world,
                                                         librdf_query_factory *factory,
                                                         const char *name,
                                                         librdf_uri *uri,
                                                         const unsigned char *query_string,
                                                         librdf_uri *base_uri);
void                librdf_free_query                   (librdf_query *query);
librdf_query_results * librdf_query_execute             (librdf_query *query,
                                                         librdf_model *model);
int                 librdf_query_get_limit              (librdf_query *query);
int                 librdf_query_set_limit              (librdf_query *query,
                                                         int limit);
int                 librdf_query_get_offset             (librdf_query *query);
int                 librdf_query_set_offset             (librdf_query *query,
                                                         int offset);

Description

Provides classes to create query objects and to execute them over an RDF graph (librdf_model) returning a librdf_query_results Query result limits and offsets can be set.

Details

librdf_query

typedef struct librdf_query_s librdf_query;

Redland query class.


librdf_query_factory

typedef struct librdf_query_factory_s librdf_query_factory;

Redland query factory class.


librdf_query_register_factory ()

void                librdf_query_register_factory       (librdf_world *world,
                                                         const char *name,
                                                         const unsigned char *uri_string,
                                                         void (*factory) (librdf_query_factory*));

Register a query factory.

world :

redland world object

name :

the query language name

uri_string :

the query language URI string (or NULL if none)

factory :

pointer to function to call to register the factory

librdf_query_language_get_description ()

const raptor_syntax_description * librdf_query_language_get_description
                                                        (librdf_world *world,
                                                         unsigned int counter);

Get a query language syntax description.

world :

librdf_world

counter :

index into the list of query language syntaxes

Returns :

description or NULL if counter is out of range

librdf_query_languages_enumerate ()

int                 librdf_query_languages_enumerate    (librdf_world *world,
                                                         const unsigned int counter,
                                                         const char **name,
                                                         const unsigned char **uri_string);

Get information on query language syntaxes.

All returned strings are shared and must be copied if needed to be used dynamically.

deprecated: use librdf_query_language_get_description() to return more information in a static structure.

world :

librdf_world

counter :

index into the list of query language syntaxes

name :

pointer to store the name of the query language syntax (or NULL)

uri_string :

pointer to store query language syntax URI string (or NULL)

Returns :

non 0 on failure of if counter is out of range

librdf_new_query ()

librdf_query *      librdf_new_query                    (librdf_world *world,
                                                         const char *name,
                                                         librdf_uri *uri,
                                                         const unsigned char *query_string,
                                                         librdf_uri *base_uri);

Constructor - create a new librdf_query object.

world :

redland world object

name :

the name identifying the query language

uri :

the URI identifying the query language (or NULL)

query_string :

the query string

base_uri :

the base URI of the query string (or NULL)

Returns :

a new librdf_query object or NULL on failure

librdf_new_query_from_query ()

librdf_query *      librdf_new_query_from_query         (librdf_query *old_query);

Copy constructor - create a new librdf_query object from an existing one

Should create a new query in the same context as the existing one as appropriate.

old_query :

the existing query librdf_query to use

Returns :

a new librdf_query object or NULL on failure

librdf_new_query_from_factory ()

librdf_query *      librdf_new_query_from_factory       (librdf_world *world,
                                                         librdf_query_factory *factory,
                                                         const char *name,
                                                         librdf_uri *uri,
                                                         const unsigned char *query_string,
                                                         librdf_uri *base_uri);

Constructor - create a new librdf_query object.

world :

redland world object

factory :

the factory to use to construct the query

name :

query language name

uri :

query language URI (or NULL)

query_string :

the query string

base_uri :

base URI of the query string (or NULL)

Returns :

a new librdf_query object or NULL on failure

librdf_free_query ()

void                librdf_free_query                   (librdf_query *query);

Destructor - destroy a librdf_query object.

query :

librdf_query object

librdf_query_execute ()

librdf_query_results * librdf_query_execute             (librdf_query *query,
                                                         librdf_model *model);

Run the query on a model.

Runs the query against the (previously registered) model and returns a librdf_query_results for the result objects.

query :

librdf_query object

model :

model to operate query on

Returns :

librdf_query_results or NULL on failure

librdf_query_get_limit ()

int                 librdf_query_get_limit              (librdf_query *query);

Get the query-specified limit on results.

This is the limit given in the query on the number of results allowed.

query :

librdf_query query object

Returns :

integer >=0 if a limit is given, otherwise <0

librdf_query_set_limit ()

int                 librdf_query_set_limit              (librdf_query *query,
                                                         int limit);

Set the query-specified limit on results.

This is the limit given in the query on the number of results allowed.

query :

librdf_query query object

limit :

the limit on results, >=0 to set a limit, <0 to have no limit

Returns :

non-0 on failure

librdf_query_get_offset ()

int                 librdf_query_get_offset             (librdf_query *query);

Get the query-specified offset on results.

This is the offset given in the query on the number of results allowed.

query :

librdf_query query object

Returns :

integer >=0 if a offset is given, otherwise <0

librdf_query_set_offset ()

int                 librdf_query_set_offset             (librdf_query *query,
                                                         int offset);

Set the query-specified offset on results.

This is the offset given in the query on the number of results allowed.

query :

librdf_query query object

offset :

offset for results, >=0 to set an offset, <0 to have no offset

Returns :

non-0 on failure


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