sparql-fiddle

a JavaScript SPARQL API and online fiddle

An online sparql-fiddle app allows you to load from URL, create, or cut and paste RDF and SPARQL into a form and then run the query, edit and re-run. It is one example of an app created with this library. Please take a look at it to see the general operation. Below is an explanation of the library that can be used in other apps. These notes are preliminary. I would REALLY like to hear comments about the API and ontology I talk about below.

Overview

A fiddle, in the context of using sparql-fiddle as a coding library, is a data structure which specifies an RDF data source, a SPARQL query, and a results format. The sparql-fiddle run() method runs the query against the data source and displays or returns the results in the specified format. The sparql-fiddle runFromLibrary() behaves similarly but retrieves the fiddle from a Turtle file library of fiddles.

Data and Query Sources

The RDF data source may be a string containing Turtle or other rdflib parseable serialization, or it may be a URL pointing to a resource containing the serialization.

Likewise, the SPARQL query may be specified as a string containing the query or a URL pointing to such a string.

Results as HTML or Text

The format for results is stored in the "wanted" key and may be one of "HTML", "Text", "Array", "Hash", "Value"

An example:

      const sf = require('sparql-fiddle') // or browser equivalent
      let fiddle = {
          data  : "http://example.com/myRDF",
          query : "http://example.com/mySPARQL",
         wanted : "HTML"
       }
       sf.run(fiddle).then( results => {
           console.log(results)
       }, err => console.log(err) )
       // 
       // output : an HTML table containing the results of the query

The HTML format shows an HTML table of results. Text shows fields one per line with a space between records. If neither of these suits your purposes, you can ask for results as an Array or a Hash and format or process them any way you'd like by iterating over the structure.

Results as an Array

The "Array" format returns an array of hashes (associative arrays). Given "SELECT ?name ?addOn ...", the results would be something like

      [ 
        {"name":"Alu Gobi","addOn":"chutney" },
        {"name":"Reuben Sandwich","addOn":"dill pickle" }
      ]

Results as a Hash

The Hash format returns a hash of hashes (associateve arrays). You need to specify a key before calling run(). If you specify fiddle.key="name" the results would be something like this:

      { 
         "Alu Gobi"        : {"name":"Alu Gobi","addOn":"chutney" },
         "Reuben Sandwich" : {"name":"Reuben Sandwich","addOn":"dill pickle" }
      }

The "Hash" format makes it very easy to read a Turtle config file into a hash object in a script.

Retrieving a Single Value

The "Value" format returns a single value. It is meant to work with a query that returns a single field in a single row. If more than one row is retrieved, only the first will be examined. If more than one field is retrieved, an arbitrary key will be returned. Here's an example:

      const sf = require('sparql-fiddle')
      let fiddle = {
            data:`@prefix : <http://schema.org/>. <> :name "hello world".`,
            query:`PREFIX : <http://schema.org/> SELECT ?y WHERE {?x :name ?y .}`,
            wanted:'Value'
      }
      sf.run(fiddle).then( res =>{ console.log(res) }, err => console.log(err) )
      //
      //  output : hello world

Default Results Format

If no "wanted" key is supplied, the results format will default to "HTML" in a browser context and "Text" in a node context.

Using N3 or RDF/XML

If the data source is not Turtle, the fiddle should specify the dataType as a mime content-type.

    fiddle.dataType = "application/rdf+xml"

Row Handlers

If you wish to munge the data before the results are returned, specify a rowHandler function which will be applied to each row during processing

    fiddle.rowHandler = function(row){
        for(r in row){ row[r] = row[r].toUpperCase() }
        return row
    }
    // values will be upper cased in results

By default, run() accumulates all rows and then returns the accumulated results. For very large results, this can eat up memory. You can, instead, handle each row as it is processed without accumulating anything. To do this, define a rowHandler which does what you need with each row but does not return anything.

    fiddle.rowHandler = function(row){
        for(r in row){ console.log(r + " : " + row[r] + "\n" }
    }
    // displays rows one at a time, as they are processed, accumulates nothing

Re-using a Store

If you want to run multiple queries against the same data, specify the data as usual in the first run and set data to be an empty string in the following runs. In this case, the rdflib store object will be reused, thus avoiding unnessary fetching and parsing which was already accomplished in the first run.

An Ontology for shareable Fiddle Libraries

Although I have not yet finalized the ontology, sparql-fiddle includes a way to store and share fiddles between Solid sources. So let's say we have a file "myLibrary.ttl" like this (ontology expressly omitted until I finalized it):

 @prefix : <#>
 <> a :FiddleLibrary.
 [] 
  a :Fiddle;
  :name "hello world";
  :data """@prefix s: <http://schema.com/>. <> s:name "hello Solid world".""";
  :query "PREFIX s: <http://schema.org/> SELECT ?msg WHERE {?x s:name ?msg.}"
.

We can now do this:

    let fiddleLibrary = "http://example.org/myLibrary.ttl"
    let options = {wanted:"Value"}
    sf.runFiddle( fiddleLibrary, "hello world", options ).then( results => {
        if( results === "hello Solid world" ) console.log("ok")
    }, err => console.log(err) )

The examples in the online app are all stored and retrieved from a fiddle library. Once an ontology is finalized, anyone will be able to create and share fiddle libraries and the examples can grow with community contributions. And other uses for fiddle libraries will hopefully appear. They can be a kind of shared stored procedure library for the community. To make these most useful, I propose some additional fields:

    :contributor   # name/email 
    :level         # beginner,intermediate,advance
    
    ... others? advice sought!

Caveats & Plans

• all SPARQL processing is based on rdflib.js which is not full SPARQL

• I have not yet implemented a secondary fetcher. This means that the data endpoint is only the original URL and its fragments, the library will not (yet) go on to fetch additional URLs listed in the original URL

Enjoy!

copyright (c) Jeff Zucker, 2018, released under MIT open source license