MarkLogic 9 Product Documentation

Node.js Application Developer's Guide — Chapter 6

Overview of Common Semantics Tasks

The following table lists some common tasks related to Semantics, along with the method best suited for the completing the task. For a complete list of interfaces, see the Node.js API Reference.

DatabaseClient.graphs.write

DatabaseClient.graphs.sparlUpdate

DatabaseClient.graphs.read

DatabaseClient.graphs.sparql

To read a graph or perform a semantic query at fixed point in time, pass a Timestamp object as a parameter to your call. For more details, see Performing Point-in-Time Operations.

Loading Triples

This topic covers using DatabaseClient.graphs.write or DatabaseClient.graphs.writeStreamto load semantic triples into the database in several formats. For a list of supported formats, see Supported RDF Triple Formats in Semantics Developer's Guide. You can also insert triples with a SPARQL Update request; for details, see Using SPARQL Update to Manage Graphs and Graph Data.

The collection lexicon must be enabled on your database when using the semantics REST services or use the GRAPH '?g' construct in a SPARQL query.

Use DatabaseClient.graphs.write to upload a block of triples to MarkLogic Server in a single request. Use DatabaseClient.graphs.writeStream to incrementally stream a large number of triples to MarkLogic Server; for details, see Streaming Into the Database. The input semantic data can be expressed as a string, object, or Readable stream.

A call to DatabaseClient.graphs.write or DatabaseClient.graphs.writeStream always includes at least a MIME type parameter indicating the format of the input triples. If you also include a graph URI, the triples are loaded into that graph. If you do not include a graph URI, the triples are loaded into the default graph. That is, you can use one of these two forms, depending on the destination graph:

// load into the default graph
db.graphs.write(mimeType, triples)
// load into a named graph
db.graphs.write(graphURI, mimeType, triples)

Optionally, you can pass a boolean repair flag. If present and set to true, MarkLogic Server attempts to repair invalid input triples during ingestion. For example:

db.graphs.write(graphURI, true, mimeType, triples)

You can also call the write functions with a call object instead of with positional parameters. The call object has the following properties:

db.graphs.write({
  uri: graphURI,             // optional, omit for default graph
  contentType: mimeType,    // required
  data: triples,            // required
  repair: boolean           // optional
})

The output from a call to DatabaseClient.graphs.write or DatabaseClient.graphs.writeStream is an object that indicates whether the triples were loaded into the default graph or a named graph. If the destination is a named graph, the graph name is returned in the graph property. For example:

// result of loading into default graph
{ defaultGraph: true, graph: null }
// result of loading into a named graph
{ defaultGraph: false, graph: 'example-graph-uri' }

The following example uses DatabaseClient.graphs.write to load a set of triples in RDF/JSON format into the default graph.

const fs = require('fs');
const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);

const triples = {
  'http://dbpedia.org/resource/Joyce_Carol_Oates' : {
    'http://dbpedia.org/property/influences' : [ {
      'type' : 'uri', 
      'value' : 'http://dbpedia.org/resource/Ernest_Hemingway' 
    } ] ,
    'http://dbpedia.org/ontology/influencedBy' : [ {
      'type' : 'uri', 
      'value' : 'http://dbpedia.org/resource/Ernest_Hemingway' 
    } ]
  },
  'http://dbpedia.org/resource/Death_in_the_Afternoon' : {
    'http://dbpedia.org/ontology/author' : [ {
      'type' : 'uri', 
      'value' : 'http://dbpedia.org/resource/Ernest_Hemingway' 
    } ] ,
    'http://dbpedia.org/property/author' : [ {
      'type' : 'uri', 
      'value' : 'http://dbpedia.org/resource/Ernest_Hemingway' 
    } ]
  }
};

db.graphs.write('application/rdf+json', triples).result(
    function(response) { 
      if (response.defaultGraph) {
        console.log('Loaded into default graph'); 
      } else {
        console.log('Loaded into graph ' + response.graph); 
      };
    },
    function(error) { console.log(JSON.stringify(error)); }
);

The following example uses DatabaseClient.graphs.writeStream to load a set of triples in N-Quads format into a named graph (example-graph). The triples are streamed from the file input.nq using a Readable stream and piped into the Writable stream returned by DatabaseClient.graphs.createWriteStream. The transaction is not committed until the all the data from the input stream is transmitted.

const fs = require('fs');
const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);
// Load into a named graph using a write stream
const writer = 
  db.graphs.createWriteStream('example-graph', 'application/n-quads');
writer.result(  
  function(response) { 
    if (response.defaultGraph) {
      console.log('Loaded triples into default graph'); 
    } else {
      console.log('Loaded triples into graph ' + response.graph); 
    };
  },
  function(error) { console.log(JSON.stringify(error)); }
);
fs.createReadStream('input.nq').pipe(writer);

To read a semantic graph, use DatabaseClient.graphs.read; for details, see Retrieving the Contents, Metadata, or Permissions of a Graph. To query semantic data, use DatabaseClient.graphs.sparql; for details, see Querying Semantic Triples With SPARQL. For additional operations, see the Node.js API Reference.

Querying Semantic Triples With SPARQL

Use the DatabaseClient.graphs.sparql method to evaluate SPARQL queries against triples in the database. For more details on using SPARQL queries with MarkLogic, see the Semantics Developer's Guide.

The collection lexicon must be enabled on your database when using the semantics REST services or use the GRAPH '?g' construct in a SPARQL query.

You can evaluate a SPARQL query by calling DatabaseClient.graphs.sparql. The query is not sent to MarkLogic for evaluation until you call result(). You can invoke the sparql method in the following ways:

// (1) db.graphs.sparql(responseContentType, query)
db.graphs.sparql(
  'application/sparql-results+json',
  'SELECT ?s ?p WHERE {?s ?p Paris }')

// (2) db.graphs.sparql(responseContentType, defaultGraphUris, query)
db.graphs.sparql(
  'application/sparql-results+json',
  'http://def/graph1', 'http://def/graph2',
  'SELECT ?s ?p WHERE {?s ?p Paris }')

// (3) db.graphs.sparql(callObject)
db.graphs.sparql({
  contentType: 'application/sparql-results+json', 
  query: 'SELECT ?s ?p WHERE {?s ?p Paris }',
  start: 0,
  length: 15
})

You must include at least a SPARQL query string and a response content type (MIME type) in your call. For a complete list of the accepted response MIME types, see SPARQL Query Types and Output Formats in the Semantics Developer's Guide.

Passing in a call object enables you to configure attributes of your query such as named graph URIs, an additional document query, result subset controls, and inference rulesets. For a complete list of the configuration properties, see graphs.sparql in the Node.js Client API Reference.

Advanced users can supply a CombinedQueryDefinition as the docQuery parameter of db.graphs.sparql. A combined query enables advanced users finer control over the optional document constraint query you can include in your query. For details, see Searching with Combined Query.

Example: SPARQL Query

The following example evaluates a SPARQL query expressed as a string literal against the default graph.

const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);

const query = [
  'PREFIX foaf: <http://xmlns.com/foaf/0.1/>' ,
  'PREFIX ppl:  <http://people.org/>' ,
  'SELECT ?personName1' ,
  'WHERE {' ,
  '    ?personUri1 foaf:name  ?personName1 ;' ,
  '                foaf:knows ppl:person3 .' ,
  '    ?personUri1 foaf:name  ?personName1 .' ,
  '    }'
];
db.graphs.sparql('application/sparql-results+json', query.join('\n')
).result(function (result) {
  console.log(JSON.stringify(result, null, 2));
}, function(error) {
  console.log(JSON.stringify(error, null, 2));
});

Running the script produces output similar to the following, given triples that indicate Person 1 and Person 2 know Person 3.

{ "head": {
    "vars": [ "personName1" ]
  },
  "results": {
    "bindings": [
      {
        "personName1": {
          "type": "literal",
          "value": "Person 1",
          "datatype": "http://www.w3.org/2001/XMLSchema#string"
        }
      },
      {
        "personName1": {
          "type": "literal",
          "value": "Person 2",
          "datatype": "http://www.w3.org/2001/XMLSchema#string"
        }
      }
    ]
}}

For more examples, see test-basic/graphs.js in the node-client-api project source directory.

Managing Graphs

This section covers the following graph management operations:

• Creating or Replacing a Graph
• Adding Triples to an Existing Graph
• Removing a Graph
• Retrieving the Contents, Metadata, or Permissions of a Graph
• Testing for Graph Existence
• Retrieving a List of Graphs

You can also use SPARQL Update to perform similar operations; for details, see Using SPARQL Update to Manage Graphs and Graph Data.

Many graph management operations only apply to managed triples.

// Add triples to a named graph
db.graphs.merge(graphUri, contentType, tripleData)

// Add triples to the default graph
db.graphs.merge(null, contentType, tripleData)

// Add triples to a named graph or the default graph using a call object
db.graphs.merge({uri: ..., contentType: ..., data: ..., ...})

const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);

const triples = [
  '@prefix p1: <http://example.org/marklogic/predicate/> .',
  '@prefix p0: <http://example.org/marklogic/people/> .',
  'p0:Julie_Smith  p1:livesIn \"Sterling\" .',
  'p0:Jim_Smith    p1:livesIn \"Bath\" .'
];
db.graphs.merge({
    uri: 'MyGraph',
    contentType: 'text/turtle',
    data: triples.join('\n'),
    repair: true
}).result(
    function(response) {
      console.log(JSON.stringify(response));
    },
    function(error) { console.log(JSON.stringify(error)); }
);

{"defaultGraph":false,"graph":"MyGraph","graphType":"named"}

const marklogic = require('marklogic');
const my = require('./my-connection.js');
const db = marklogic.createDatabaseClient(my.connInfo);

db.graphs.remove('example-graph').result(
  function(response) { console.log(JSON.stringify(response)); }
);
// expected output:
// {"defaultGraph":false,"graph":"example-graph"}

const marklogic = require('marklogic');
const my = require('./my-connection.js');
const db = marklogic.createDatabaseClient(my.connInfo);

db.graphs.remove().result(
  function(response) { console.log(JSON.stringify(response)); }
);
// expected output: 
// {"defaultGraph":true,"graph":null}

// (1) Retrieve all triples in the default graph
db.graphs.read(responseContentType)

// (2) Retrieve all triples in a named graph
db.graphs.read(uri, responseContentType)

// (3) Retrieve triples, metadata, or permissions using a call object
db.graphs.read({contentType: ..., ...})

const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);

db.graphs.read('MyGraph','text/turtle')
  .result(
    function(response) {
      for (const line of response.split('\n')) {
        console.log(line);
      }
    },
    function(error) { console.log(JSON.stringify(error)); }
  );

db.graphs.read({
  uri: 'MyGraph',
  contentType: 'application/json',
  category: 'metadata'
});

db.graphs.probe('http://marklogic.com/example/graph')
  .result(
    function(response) {
      console.log(JSON.stringify(response));
    },
    function(error) { console.log(JSON.stringify(error)); }
  );

{ "contentType": null,
  "contentLength": null,
  "versionId": null,
  "location": null,
  "systemTime": null,
  "exists": true,
  "defaultGraph": false,
  "graph": "http://marklogic.com/example/graph",
  "graphType": "named"
}

{ "exists": false,
  "defaultGraph": false,
  "graph": "NoMyGraph",
  "graphType": "named"
}

const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);

db.graphs.list('text/uri-list')
  .result(
    function(response) {
      for (const uri of response.split('\n')) {
        console.log(uri);
      }
    },
    function(error) { console.log(JSON.stringify(error)); }
);

"MyGraph\nhttp://marklogic.com/semantics#graphs\n"

Using SPARQL Update to Manage Graphs and Graph Data

You can use a SPARQL Update request to manage graphs and graph data from Node.js by calling DatabaseClient.graphs.sparqlUpdate. You can only use this interface to work with managed triples. You can also manage graphs and graph data without using SPARQL Update; for details, see Managing Graphs and Loading Triples.

You can call graphs.sparqlUpdate in the following ways:

// (1) pass only the SPARQL Update as a string or ReadableStream
db.graphs.sparqlUpdate(updateOperation)

// (2) pass a call config object that includes the SPARQL Update
db.graphs.sparqlUpdate({data: updateOperation, ...})

The call object pattern enables you to control operations details, such as permissions, inferencing rulesets, transaction control, and variable bindings. When you use a call object, the data property holds your SPARQL Update request string or stream.

The following example creates a graph, passing in only a SPARQL Update request.

const marklogic = require('marklogic');
const my = require('./my-connection.js');

const db = marklogic.createDatabaseClient(my.connInfo);

db.graphs.sparqlUpdate(
    'CREATE GRAPH <http://marklogic.com/semantics/tutorial/update> ;'
).result(
    function(response) { 
      console.log('Graph created.');
      console.log(JSON.stringify(response));
    },
    function(error) { console.log(JSON.stringify(error)); }
);

Running this script produces the following output:

Graph created.
{"defaultGraph":false,"graph":null,"graphType":"inline"}

The following example uses a call object to create a graph and insert triples. The call object defines permissions on the graph, and defines variable bindings used in the SPARQL Update request.

const graphURI = 'http://marklogic.com/sparqlupd/example';
db.graphs.sparqlUpdate({
    data: 
      'CREATE GRAPH <' + graphURI + '> ;' +
      'INSERT {GRAPH <' + graphURI + '> {?s ?p ?b1 }} '+
      'WHERE  {GRAPH <' + graphURI + '> ' +
          '{?s ?p ?o. filter (?p = ?b2) }}',
    bindings: { 
      b1: 'bindval1', 
      b2: {value: 'bindval2', type: 'string'}
    },
    permissions: [
      { 'role-name': 'app-user', capabilities: ['read']},
      { 'role-name': 'admin', capabilities: ['read','update']},
    ]
})

For a complete list of configuration properties usable in the call object, see graphs.sparqlUpdate in the Node.js Client API Reference.

For more details on using SPARQL Update with MarkLogic, see SPARQL Update in the Semantics Developer's Guide.

Applying Inferencing Rules to a SPARQL Query or Update

You can specify one or more inferencing rulesets to apply to a SPARQL query or SPARQL Update request. Inference rules enable you to discover new facts about your data at query or update time.

SPARQL inference is discussed in detail in Inference in the Semantics Developer's Guide. This section only covers usage details specific to the Node.js Client API.

The following topics are covered:

• Basic Inference Ruleset Usage
• Example: SPARQL Query With Inference Ruleset
• Example: SPARQL Update With Inference Rulesets
• Controlling the Default Database Ruleset

db.graphs.sparql({'content-type': ..., query: ..., rulesets: ...})

db.graphs.sparqlUpdate({data: ..., rulesets: ...})

db.graphs.sparql({
  contentType: 'application/sparql-results+json', 
  query: 'SELECT ?s ?p WHERE {?s ?p Paris }',
  rulesets: 'subPropertyOf.rules'
})

const update = [
  PREFIX exp: <http://example.org/marklogic/people> 
  PREFIX pre: <http://example.org/marklogic/predicate>
  INSERT DATA {
    GRAPH <MyGraph>{
      exp:John_Smith pre:livesIn "London" .
      exp:Jane_Smith pre:livesIn "London" .
      exp:Jack_Smith pre:livesIn "Glasgow" .
  }}
];
db.graphs.sparqlUpdate({
  data: update.join('\n'),
  rulesets: ['sameAs.rules', '/my/rules/custom.rules']
})

db.graphs.sparql({
  contentType: 'application/sparql-results+json', 
  query: 'SELECT ?s ?p WHERE {?s ?p Paris }',
  rulesets: 'subPropertyOf.rules',
  defaultRuleSets: 'exclude'
})