SPARQL source¶

The SPARQL source fetches RDF data about subjects from a triplestore exposing a SPARQL compliant endpoint. The endpoint of the source is configured either directly or implicitly by a URL system. The source uses two SPARQL queries to construct entities; the fragment query is a SPARQL SELECT query that gets a list of subjects to get data for and their modification times and a fragment query, which is a SPARQL CONSTRUCT query that gathers all relevant statements about a particular subject. The latter is then used to generate the stream of entities.

See the Working with RDF document for more detail on working with RDF in Sesam.

Prototype¶

{
    "type": "sparql",
    "system": "url-system-id",
    "url": "sparql-endpoint",
    "fragments_query": "SPARQL select query",
    "fragment_query": "SPARQL construct query"
    "initial_since_value": "0001-01-01T00:00:00Z"
}

Properties¶

Property	Type	Description	Default	Req
`system`	String	The id of the URL System component to use.		Yes
`fragments_query`	List<String> or String	A SPARQL `SELECT` query that should return exactly two bound variables: `id` which should contain a unique subject and `updated` which should contain its modification time in ISO UTC format (or “0001-01-01T00:00:00Z” if not available in the data). If you would like the source to have continuation support, then you must include a filter based on the `updated` content compared to the current since moniker. You must use a variable expansion `${since}` for this purpose. The query result set should always be ordered by the “?updated” variable. If a list of strings is given, they will be converted to a single string by concatenation with the newline character.		Yes
`fragment_query`	List<String> or String	A SPARQL `CONSTRUCT` query that should return all the relevant statements for a particular subject selected by the `fragments_query` query. The query should use the expansion variable “${uri}” to filter or select the correct subject to construct the statements to return. If a list of strings is given, they will be converted to a single string by concatenation with the newline character.		Yes
`initial_since_value`	String	A string literal to use when querying the triplestore the first time.	“0001-01-01T00:00:00Z”

Continuation support¶

See the section on continuation support for more information.

Property	Value
`supports_since`	`false` (Dynamic: `true` if `${since}` in `fragments_query`)
`is_since_comparable`	`true` (Default)
`is_chronological`	`false` (Default)

Example configuration¶

The outermost object would be your pipe configuration, which is omitted here for brevity.

{
    "source": {
        "type": "sparql",
        "url": "http://localhost:8890/sparql",
        "fragments_query": [
            "PREFIX sdshare: <http://www.sdshare.org/2012/extension/>",
            "SELECT DISTINCT ?id ?updated WHERE {",
             "    ?id sdshare:lastmodified ?updated",
             "} FILTER (?updated >= \"${since}\"^^xsd:dateTime) ORDER BY ?updated",
        ],
        "fragment_query": [
            "CONSTRUCT { ?subject ?property ?value } WHERE {",
            "  ?subject ?property ?value .",
            "} FILTER (?subject = <${uri}>)",
        ]
    },
}

HTTP endpoint source

REST source (experimental)