Traqula algebra transformations 1.1

Traqula algebra transformations contains translation functions for translating the Traqula AST into SPARQL Algebra. The algebra rules and algebra definitions are derived from SPARQLAlgebra.js.

Installation

npm install @traqula/algebra-transformations-1-1

or

yarn add @traqula/algebra-transformations-1-1

Algebra object

The algebra object contains a types object, which contains all possible values for the type field in the output results. Besides that it also contains all the TypeScript interfaces of the possible output results.

The best way to see what output would be generated is to look in the test folder, where we have many SPARQL queries and their corresponding algebra output.

Deviations from the spec

This implementation tries to stay as close to the SPARQL 1.1 specification, but some changes were made for ease of use. These are mostly based on the Jena ARQ implementation. What follows is a non-exhaustive list of deviations:

Named parameters

This is the biggest visual change. The functions no longer take an ordered list of parameters but a named list instead. The reason for this is to prevent having to memorize the order of parameters and also due to seeing some differences between the spec and the Jena ARQ SSE output when ordering parameters.

Multiset/List conversion

The functions toMultiset and toList have been removed for brevity. Conversions between the two are implied by the operations used.

Quads

The translate function has an optional second parameter indicating whether patterns should be translated to triple or quad patterns. In the case of quads the graph operation will be removed and embedded into the patterns it contained. The default value for this parameter is false.

PREFIX : <http://www.example.org/>

SELECT ?x WHERE {
    GRAPH ?g {?x ?y ?z}
}

Default result:

{
  "type": "project",
  "input": {
    "type": "graph",
    "input": {
      "type": "bgp",
      "patterns": [{
        "type": "pattern",
        "termType": "Quad",
        "subject": { "termType": "Variable", "value": "x" },
        "predicate": { "termType": "Variable", "value": "y" },
        "object": { "termType": "Variable", "value": "z" },
        "graph": { "termType": "DefaultGraph", "value": "" }
      }]
    },
    "name": { "termType": "Variable", "value": "g" }
  },
  "variables": [{ "termType": "Variable", "value": "x" }]
}

With quads:

{
  "type": "project",
  "input": {
    "type": "bgp",
    "patterns": [{
      "type": "pattern",
      "termType": "Quad",
      "subject": { "termType": "Variable", "value": "x" },
      "predicate": { "termType": "Variable", "value": "y" },
      "object": { "termType": "Variable", "value": "z" },
      "graph": { "termType": "Variable", "value": "g" }
    }]
  },
  "variables": [{ "termType": "Variable", "value": "x" }]
}

Flattened operators

Several binary operators that can be nested, such as the path operators, can take an array of input entries to simply this notation. For example, the following SPARQL:

SELECT * WHERE { ?x <a:a>|<b:b>|<c:c> ?z }

outputs the following algebra:

{
  "type": "project",
  "input": {
    "type": "path",
    "subject": { "termType": "Variable", "value": "x" },
    "predicate": {
      "type": "alt",
      "input": [
        { "type": "link", "iri": { "termType": "NamedNode", "value": "a:a" } },
        { "type": "link", "iri": { "termType": "NamedNode", "value": "b:b" } },
        { "type": "link", "iri": { "termType": "NamedNode", "value": "c:c" } }
      ]
    },
    "object": { "termType": "Variable", "value": "z" },
    "graph": { "termType": "DefaultGraph", "value": "" }
  },
  "variables": [
    { "termType": "Variable", "value": "x" },
    { "termType": "Variable", "value": "z" }
  ]
}

VALUES

For the VALUES block we return the following output:

PREFIX dc:   <http://purl.org/dc/elements/1.1/>
PREFIX :     <http://example.org/book/>
PREFIX ns:   <http://example.org/ns#>

SELECT ?book ?title ?price
{
   VALUES ?book { :book1 :book3 }
   ?book dc:title ?title ;
         ns:price ?price .
}

{
  "type": "project",
  "input": {
    "type": "join",
    "input": [
      {
        "type": "values",
        "variables": [{ "termType": "Variable", "value": "book" }],
        "bindings": [
          { "book": { "termType": "NamedNode", "value": "http://example.org/book/book1" } },
          { "book": { "termType": "NamedNode", "value": "http://example.org/book/book3" } }
        ]
      },
      {
        "type": "bgp",
        "patterns": [
          {
            "type": "pattern",
            "termType": "Quad",
            "subject": { "termType": "Variable", "value": "book" },
            "predicate": { "termType": "NamedNode", "value": "http://purl.org/dc/elements/1.1/title" },
            "object": { "termType": "Variable", "value": "title" },
            "graph": { "termType": "DefaultGraph", "value": "" }
          },
          {
            "type": "pattern",
            "termType": "Quad",
            "subject": { "termType": "Variable", "value": "book" },
            "predicate": { "termType": "NamedNode", "value": "http://example.org/ns#price" },
            "object": { "termType": "Variable", "value": "price" },
            "graph": { "termType": "DefaultGraph", "value": "" }
          }
        ]
      }
    ]
  },
  "variables": [
    { "termType": "Variable", "value": "book" },
    { "termType": "Variable", "value": "title" },
    { "termType": "Variable", "value": "price" }
  ]
}

Differences from Jena ARQ

Some differences from Jena (again, non-exhaustive): no prefixes are used (all uris get expanded) and the project operation always gets used (even in the case of SELECT *).