package rdf

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package rdf
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Sparql queries.

Error handling

type error =
  1. | Parse_error of Loc.loc * string
  2. | Value_error of Dt.error
  3. | Eval_error of Sparql_eval.error
  4. | Algebra_error of Sparql_algebra.error
  5. | Not_select
  6. | Not_ask
  7. | Not_construct
  8. | Not_describe
  9. | Not_get
  10. | Not_update
  11. | Not_implemented of string
exception Error of error
val string_of_error : error -> string

Parsing and printing Sparql queries

type query = Sparql_types.query
val query_from_string : string -> query
val query_from_file : string -> query
val string_of_query : query -> string

Executing queries

Solutions

type solution
val get_term : solution -> string -> Term.term

get_term solution varname returns the Term.term bound to varname in the solution.

  • raises Not_found

    if the variable is not bound.

val is_bound : solution -> string -> bool

is_bound solution varname returns whether the given variable name is bound in the solution.

val solution_fold : (string -> Term.term -> 'a -> 'a) -> solution -> 'a -> 'a

solution_fold f sol acc is f var1 term1 (f var2 term2 (...) acc), folding over the bindings of the solution.

val solution_iter : (string -> Term.term -> unit) -> solution -> unit

solution_iter f solution calls f on each pair (varname, term) of the solution.

Convenient functions to access solution bindings.

All these functions can raise Dt.Error exceptions in case the term bounded to the variable name is not compatible with the asked type.

The functions are just calls to Dt functions. For example, get_int retrieve the bounded term with get_term, then calls Dt.of_term to get a Dt.value, than calls Dt.int to retrieve an Int n value, then return n.

val get_string : solution -> string -> string
val get_iri : solution -> Iri.t -> string -> Iri.t

See comment of Dt.iri.

val get_int : solution -> string -> int
val get_float : solution -> string -> float
val get_bool : solution -> string -> bool
val get_datetime : solution -> string -> Term.datetime
val get_ltrl : solution -> string -> string * string option

Same as get_string but the associated language tag is kep, if any.

Querying

type query_result =
  1. | Bool of bool
  2. | Solutions of solution list
  3. | Graph of Graph.graph
val execute : ?graph:Graph.graph -> base:Iri.t -> Ds.dataset -> query -> query_result

execute ~base dataset q executes the sparql query q on dataset, using base as base iri. The form of the result depends on the kind of query:

  • Select queries return a Solution solutions
  • Ask queries return a Bool bool
  • Construct queries return Graph g.
  • Describe queries return a description graph.

For Construct and Describe queries, if a graph is provided, it is filled and the same graph is returned; else a new graph (in memory) is created, filled and returned. If the graph is created, it iri is the base iri provided.

Warning: Describe queries are not implemented yet.

  • raises Error

    in case of error.

val execute_update : graph:Graph.graph -> query -> query_result

Convenient functions for querying

val select : base:Iri.t -> Ds.dataset -> query -> solution list

Execute the given SELECT query.

val construct : ?graph:Graph.graph -> base:Iri.t -> Ds.dataset -> query -> Graph.graph

Execute the given CONSTRUCT query.

val ask : base:Iri.t -> Ds.dataset -> query -> bool

Execute the given ASK query.

  • raises Not_ask

    is the query is not a ASK.

val describe : ?graph:Graph.graph -> base:Iri.t -> Ds.dataset -> query -> Graph.graph

Execute the given DESCRIBE query.

Predefined functions

These are the functions named by an IRI, see details here.

type iri_fun = Dt.value list -> Dt.value

A function takes a list of values and returns a value.

val iri_funs : unit -> iri_fun Iri.Map.t
val add_iri_fun : Iri.t -> iri_fun -> unit