How do I insert a triplet into a specific XML document?

First, the key here is to recognize that there are two ways to store and manage triplets in MarkLogic.

• driven triplets - this is where you want to use MarkLogic as "just a triple store". You load triplets with mlcp (command line loader) or sem: rdf-load () or sem: rdf-insert (). In this case, you don't want to know or care about the documents that store the triplets - you just want to download the triplets so that you can query them later using SPARQL. Therefore sem: rdf-insert () has no "insert into this document" argument.

• inline triplets - triplets are embedded in an XML (or JSON) document. In this case, the troika is conceptually part of the document; so if you want to insert a triplet into a document (insert a triplet into a document), you should look for document processing APIs, not triples APIs.

Once you have this mental model, you can use sem: rdf-insert () if your triple is essentially "free floating", meaning it doesn't matter which document it is in. Or you can use something like xdmp: node-insert-child () if you really want to place this triplet inside an existing document at some position. (In MarkLogic 8, you can also use SPARQL Update to insert managed / free floating triplets.

However, I wanted to see if I could make the node-internet-child in a simpler and more intuitive way, i.e. without the "trick" above.

First, it is helpful to create a triple using sem: iri () and sem: triple () above, although you could create a triple in XML directly. Using sem constructors: more reliable.

Second, sem: triple () returns an object of type sem: triple, not an XML node. Therefore, you cannot pass it to xdmp: node-insert-child () directly. But there is a helper function for translating from sem: triple to XML node - sem: rdf-serialize () with the "triplexml" option.

So, you can do this:

xdmp:document-insert( "/test/test.xml", <doc><title>test</title></doc>)

      

        
        
        
      

    

then

import module namespace sem = "http://marklogic.com/semantics" 
      at "/MarkLogic/semantics.xqy";

xdmp:node-insert-child(
  fn:doc('/test/test.xml')/doc,
  sem:rdf-serialize(
      sem:triple(sem:iri("Firefly"), "is-a", "TV show"),
      "triplexml"
      )
)

      

        
        
        
      

    

... and you get:

fn:doc('/test/test.xml')

      

        
        
        
      

    

=>

<doc>
  <title>test</title>
  <sem:triples xmlns:sem="http://marklogic.com/semantics">
    <sem:triple>
      <sem:subject>Firefly</sem:subject>
      <sem:predicate datatype="http://www.w3.org/2001/XMLSchema#string">is-a</sem:predicate>
      <sem:object datatype="http://www.w3.org/2001/XMLSchema#string">TV show</sem:object>
    </sem:triple>
  </sem:triples>
</doc>