how to query virtual graphs

[gh....@gmail.com]

Hi,

I am testing the virtual graph feature of Stardog 4.0.3 (developer version).

I managed to create a virtual graph following the instructions on http://docs.stardog.com/#_virtual_graphs

$ ./stardog-admin virtual list

+----------------+

| Virtual Graphs |

+----------------+

| virtual://dept |

+----------------+

1 virtual graphs

However, when I try to query it, I got a problem

$ ./stardog query  'SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }'

No driver was found which supports the connection string: 'SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }', please double-check the URL and verify the protocol is correct and try again.

$ ./stardog query dept 'SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }'

Database 'dept' does not exist.

How should I issue the query from command line?

Thanks in advance!

Guohui

[Zachary Whitley]

On Mon, Feb 1, 2016 at 12:20 PM, <gh....@gmail.com> wrote:

Hi,

I am testing the virtual graph feature of Stardog 4.0.3 (developer version).

I managed to create a virtual graph following the instructions on http://docs.stardog.com/#_virtual_graphs

$ ./stardog-admin virtual list

+----------------+

| Virtual Graphs |

+----------------+

| virtual://dept |

+----------------+

1 virtual graphs

However, when I try to query it, I got a problem

$ ./stardog query  'SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }'

No driver was found which supports the connection string: 'SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }', please double-check the URL and verify the protocol is correct and try again.

You need to specify a database name to query against which is correct below.

 

$ ./stardog query dept 'SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }'

Database 'dept' does not exist.

How should I issue the query from command line?

It looks like the command is correct and the response is telling you what the problem is. You probably haven't created a database named "dept". An empty one will do. You can't issue a query without specifying a database.

(I did notice looking at the man page for "stardog query" that the execute portion isn't marked as optional "stardog query [execute]" which it is)

 

Thanks in advance!

Guohui

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[Guohui Xiao]

Thanks for the tip. I created an empty database and I am able to query.

$ ./stardog query execute dept 'prefix emp: <http://example.com/emp/> SELECT * { GRAPH <virtual://dept> { ?person a emp:Employee } }'

+-----------------------------+

|           person            |

+-----------------------------+

| http://example.com/emp/7369 |

+-----------------------------+

Query returned 1 results in 00:00:00.095

One comment is that I had to use ansi mode in the connection string in dept.properties:

jdbc.url=jdbc\:mysql\://localhost/dept?sessionVariables=sql_mode='ansi'

Otherwise, it complains about the generated SQL syntax.

Regards,

Guohui

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--

Guohui Xiao, PhD
Assistant Professor with a fixed-term contract
KRDB - Faculty of Computer Science        
Free University of Bozen-Bolzano
Piazza Domenicani, 3                
I-39100 Bolzano, Italy    

http://www.ghxiao.org