package com.data2semantics.yasgui.server.fetchers.endpoints;
/*
* #%L
* YASGUI
* %%
* Copyright (C) 2013 Laurens Rietveld
* %%
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
* #L%
*/
import java.io.IOException;
import java.util.Iterator;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.data2semantics.yasgui.server.SparqlService;
import com.data2semantics.yasgui.shared.Endpoints;
import com.hp.hpl.jena.query.QuerySolution;
import com.hp.hpl.jena.query.ResultSet;
public class CkanFetcher {
private static String ENDPOINT_CKAN = "http://semantic.ckan.net/sparql";
public static String fetch() throws JSONException, IOException {
JSONArray endpoints = new JSONArray();
ResultSet resultSet = queryCkan();
while (resultSet.hasNext()) {
JSONObject endpointObject = new JSONObject();
QuerySolution querySolution = resultSet.next();
Iterator<String> varNames = querySolution.varNames();
while (varNames.hasNext()) {
String varName = varNames.next();
endpointObject.put(varName, EndpointsFetcher.getBindingValueAsString(querySolution.get(varName)));
}
endpoints.put(endpointObject);
}
if (endpoints.length() == 0) {
throw new IOException("No endpoints retrieved from Ckan");
}
return endpoints.toString();
}
public static ResultSet queryCkan() {
return SparqlService.query(ENDPOINT_CKAN, getCkanQuery());
}
private static String getCkanQuery() {
return "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>\n"
+ " PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>\n"
+ " PREFIX dcat: <http://www.w3.org/ns/dcat#>\n"
+ " PREFIX dcterms: <http://purl.org/dc/terms/>\n" + "\n"
+ " SELECT DISTINCT ?" + Endpoints.KEY_DATASETURI + " ?" + Endpoints.KEY_TITLE + " ?" + Endpoints.KEY_DESCRIPTION + " ?" + Endpoints.KEY_ENDPOINT + " {\n"
+ " ?" + Endpoints.KEY_DATASETURI + " dcat:distribution ?distribution.\n"
//hmm, there are multiple dataset uris per endpoint, and no proper way to distinguish between them
//to avoid having multiple results per endpoint, only retrieve the datasets with the datahub.io dataset uri
+ " FILTER regex(str(?" + Endpoints.KEY_DATASETURI + "), \"^http://datahub.io\") ."
+ " ?distribution dcterms:format ?format.\n"
+ " ?format rdf:value 'api/sparql'.\n"
+ " ?distribution dcat:accessURL ?" + Endpoints.KEY_ENDPOINT + ".\n"
+ " ?" + Endpoints.KEY_DATASETURI + " dcterms:title ?" + Endpoints.KEY_TITLE + ";\n"
+ " dcterms:description ?" + Endpoints.KEY_DESCRIPTION + ".\n" +
" } ORDER BY ?" + Endpoints.KEY_TITLE;
}
public static void main(String[] args) {
try {
System.out.println(CkanFetcher.fetch());
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
}
}