queryingPaths.md

Querying Over Paths of Nested Graphs

The following examples demonstrate querying paths in nested graphs. This investigates the issue that Olaf raised in his formalization. The good news is that the issue seems under control. The bad news is it seems that it's not as easy as hoped for to query over multiple (nested) graphs. It's not hard - always the same pattern, e.g. in the second example below { graph nng:embeddings { ?root nng:transcludes* ?what . } } - but it's not pretty either. To make it nicer requires an addition to SPARQL, and we haven't got a prototype for that yet.

:Z {
    :Y {
        :X { 
            :Dog :eats :Fish .
            THIS :says :Alice ;
                 nng:domain [ :name "Dodger" ]
        } :says :Bob ;
          :believes :Ben .
        :Goat :has :Ideas .
        :Beatrice :claims [] {" :Jake :knows :Larry . 
                                :Larry a :Star . "} .
    } :says :Carol ;
      :believes :Curt ;
      nng:tree :Example .
} :says :Zarathustra  ,
  :source :Source_1 .

Note

The fragment identifier nng:tree is not implemented yet. Its purpose is to annotate a graph and all nested graphs recursively.

In the following some example queries are given, together with different versions of expected results and the respective query. A complete documentation of Dydra's implementation of the queries and their results plus some comments is available in the query shell script.

Prefix declarations are always

prefix : <http://example.org/> 
prefix nng: <http://nested-named-graph.org/>
prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>

1) who says ':Dog :eats :Fish .' ?

Expected results are:

> :Alice                            # give me only the result(s) from the THIS level
> :Alice :Bob :Carol :Zarathustra   # give me results on all levels of nesting
> :Alice :Bob                       # give me results from the first n=2 levels of nesting
                                    # nesting level count starts inside a graph 
                                    # (to account e.g. for self references like THIS)

For the complete example see query shell script line 39 ff.

Respective queries are:

give me only the result(s) from the THIS level

select ?who
from included nng:NestedGraph
where {
  { :Dog :eats :Fish . } :says ?who .
}

See query shell script line 87 ff.

give me results on all levels of nesting

select ?orator
from named all
where {
  { graph ?what { :Dog :eats :Fish . } }
  { graph nng:embeddings { ?root nng:transcludes* ?what . } }
  { graph ?venue { ?root :says ?orator } }
}

See query shell script starting from line 106, in particular 167 ff.

give me results from the first n=2 levels of nesting

nesting level count starts with THIS

select ?what ?root ?orator
from named all
where {
  { graph ?what { :Dog :eats :Fish . } }
  { graph nng:embeddings { ?root nng:transcludes{0,1} ?what . } }
  { graph ?root { ?about :says ?orator } }
}

See query shell script line 185 ff.

2) who believes ':Dog :eats :Fish .' ?

Expected results are:

>                                   # give me only the result(s) from the THIS level
> :Ben :Curt                        # give me results on all levels of nesting
> :Ben                              # give me results from the first n=2 levels of nesting
                                    # nesting level count starts with THIS

For the complete example see query shell script line 206 ff.

Respective queries are:

give me only the result(s) from the THIS level

[TODO]

give me results on all levels of nesting

select ?orator
from named all
where {
  { graph ?what { :Dog :eats :Fish . } }
  { graph nng:embeddings { ?root nng:transcludes* ?what . } }
  { graph ?venue { ?root :believes ?orator } }
}

See query shell script line 215 ff.

give me results from the first n=2 levels of nesting

nesting level count starts with THIS

select ?orator
from included nng:NestedGraph
where {
  { graph ?what { :Dog :eats :Fish . } }
  { graph ?venue { ?what :believes ?orator } }
}

See query shell script line 248 ff.

3) in which graph(s) occurs ':Goat :has ?o' ?

Expected results are:

>                                   # give me only results annotated with THIS
> :Y                                # give me only the nearest graph
> :Y :Z                             # give me all enclosing graphs (Olaf's case 3)
                                    # BUT not the DEFAULT graph, because :Z is not nested 
                                    #   in the default graph

For the complete example see query shell script line 266 ff.

Respective queries are:

give me only results annotated with THIS

select ?what
where {
  { graph ?what { :Goat :has ?o . ?what ?annotated ?with} }
}

See query shell script line 276 ff.

give me only the nearest graph

select ?what
where {
  { graph ?what { :Goat :has ?o . } }
}

See query shell script line 290 ff.

give me all enclosing graphs but NOT the DEFAULT graph

select distinct ?what ?root
where {
  { graph ?what { :Goat :has ?o . } }
  { graph nng:embeddings { ?root nng:transcludes* ?what . } }
}

See query shell script line 304 ff.

4) what does Curt believe?

Expected results are:

> :Y

Respective queries are:

[TODO] 

5) which graphs are of type :Example ?

Expected results are:

> :Y :X _:Report1                   # _:Report1 referring to Beatrice' claim

Respective queries are:

[TODO] 

6) give me all types

Expected results are:

> :Example _:b1                     # the value space of fragment identifiers nng:domain
                                    # and nng:tree is interpreted as class
                                    # _:b1 refers to the dog named "Dodger"

Respective queries are:

[TODO] 

7) give me all types including from included graph literals

    > :Example, :Star

Respective queries are:

[TODO]