[jira] [Commented] (JENA-632) Generate JSON from SPARQL directly.

["Bruno P. Kinoshita (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JENA-632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14268654#comment-14268654 ] 

Bruno P. Kinoshita commented on JENA-632:
-----------------------------------------

Hello

The grammar has been [updated|https://github.com/kinow/jena/commit/ad17a099a1c5fb6577a02edc311ff8ceeaa08183#diff-a55ff4fd4c62d2b74b34605f07294920] and it now supports the following syntax:

{noformat}
JSON { "name": ?name } WHERE { ?name ?a ?b } LIMIT 3
{noformat}

The {{LOOKAHEAD(2)}} is no longer necessary, thanks to Andy's suggestion :-) and I now, after changing it, find JSON easier to understand and avoid mistakes than SELECT JSON.

{noformat}
[1] QueryUnit    ::= Query
[2] Query           ::= Prologue ( SelectQuery | ConstructQuery | DescribeQuery | AskQuery | JsonQuery ) ValuesClause
[...] ...
{noformat}

Q1) Does that look correct?

I've debugged it, and found that, considering that this grammar is correct for what is proposed in this issue, the next step would be update {{SPARQL_Query#executeQuery()}}, and prepare the [JSON result|https://github.com/kinow/jena/blob/99ff26d52cdaaca4a4094c247a161349c9f500f4/jena-fuseki/src/main/java/org/apache/jena/fuseki/servlets/SPARQL_Query.java#L328].

I'm temped to re-use what SPARQL_Query does when the query type is select, and simply replace the variable names by the ones provided by the user. i.e.

{noformat}
JSON { "name": ?abcde } WHERE { ?abcde ?a ?b }
{noformat}

In the example above, I'd replace the var "abcde" by "name" before serializing the result. 

Q2) Does that sound like a good plan?

Talking about the serialization... in Fuseki, users define the serialization type (xml, text/plan, json, etc). 

Q3) Should we enforce JSON when the user uses a JSON query? I think it is not necessary, maybe we can simply return the result set with the changed variables.

Q4) And finally, is it safe and correct to use the {{JSONOutput#format}} to return the result of the JSON query? I think the result will be similar to:

**query:**

{noformat}
JSON { "name": ?a } WHERE { ?a ?b ?c }
{noformat}

**result:**

{noformat}
{
  "head": {
    "vars": [ "name" ]
  } ,
  "results": {
    "bindings": [
      {
        "name": { "type": "uri" , "value": "http://example.org/book/book5" }
      } ,
      {
        "name": { "type": "uri" , "value": "http://example.org/book/book5" }
      } ,
      {
        "name": { "type": "uri" , "value": "http://example.org/book/book3" }
      }
    ]
  }
}
{noformat}

Reading the old comments here and the post in the fist comment, I think maybe we should use something new (or add some new method somewhere) to return something close to:

{noformat}
{
  "head": {
    "vars": [ "name" ]
  } ,
  "results": {
    "bindings": [
      {
          "name": "http://example.org/book/book5"
      },
      {
          "name": "http://example.org/book/book5"
      },
      {
          "name": "http://example.org/book/book3"
      }
    ]
  }
}
{noformat}

Thanks!

> Generate JSON from SPARQL directly.
> -----------------------------------
>
>                 Key: JENA-632
>                 URL: https://issues.apache.org/jira/browse/JENA-632
>             Project: Apache Jena
>          Issue Type: Improvement
>          Components: ARQ, Fuseki
>            Reporter: Andy Seaborne
>            Priority: Minor
>              Labels: gsoc, java, javacc
>
> The capability to generate JSON directly from a SPARQL (or extended SPARQL) query would enable the creation of JSON data API over published linked data.
> This project would cover:
> # Design and publication of a design.
> # Refinement of design based on community feed
> # Implementation, including testing.
> # Refinement of implementation based on community feed
> Skills required: Java, some parser work, design and discussion with the user community, basic understanding of HTTP and content negotiation.



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