Graph data API operation

[benjamingeer]

This implements the API operation /v1/graphdata/, which returns a graph of resources that are reachable from a certain resource.

• The depth of the search is configurable in the request (via the ?depth query parameter, currently not used in the SALSAH GUI, so it defaults to a depth of 4).
• The graph includes both outbound and inbound links.
• The graph includes any link that's a subproperty of knora-base:hasLinkTo, except:
  • If resource R1 knora-base:isPartOf resource R2, no link from R1 to R2 is included in the graph.
• The graph excludes deleted resources and links, as well as resources and links that the user doesn't have permission to see.

The old SALSAH GUI used arbor.js to render the graph in JavaScript. Since that library hasn't been updated in 5 years, I've replaced it with the better-maintained and easier-to-use Cytoscape library.

After much experimentation with different SPARQL query designs (see #269), this implementation uses simple recursive SPARQL queries. I haven't tested it with a huge graph, but performance seems OK for graphs that aren't very big. To improve performance, it doesn't return resource properties (as the old SALSAH did). RDFS inference is also used on GraphDB for better performance.

I also did a little refactoring so the responders no longer decide whether to use inference, in the interest of simplifying the responders. Since not every triplestore offers this choice on a per-query basis, I think it's better to assume that either the repository was created with inference enabled or it wasn't. So now the store package enables inference only with GraphDB, and it's up to the templates to disable it if they don't want it (which they currently do anyway).

Closes #269.

[tobiasschweizer]

I have a problem regarding permissions. I wanted to open http://localhost:3333/v1/graphdata/http%3A%2F%2Fdata.knora.org%2Fa-thing-with-text-values in graph view, but did not see any results. I am logged in as anything-user.

These two API requests give me all information about the resources (including the links):
http://localhost:3333/v1/resources/http%3A%2F%2Fdata.knora.org%2Fa-thing-with-text-values
http://localhost:3333/v1/resources/http%3A%2F%2Fdata.knora.org%2Fa-thing

But the request to graph view gives me an empty result
http://localhost:3333/v1/graphdata/http%3A%2F%2Fdata.knora.org%2Fa-thing-with-text-values

{
    "nodes": [],
    "edges": [],
    "userdata": {
        "email": "anything.user01@example.org",
        "username": "anything-user",
        "firstname": "Anything",
        "projects_info": [{
            "basepath": null,
            "shortname": "anything",
            "description": null,
            "logo": null,
            "id": "http://data.knora.org/projects/anything",
            "keywords": null,
            "rights": null,
            "longname": "Anything Project"
        }],
        "user_id": "http://data.knora.org/users/9XBCrDV3SRa7kS1WwynB4Q",
        "lastname": "User01",
        "token": null,
        "active_project": null,
        "projects": ["http://data.knora.org/projects/anything"],
        "lang": "de",
        "password": null
    },
    "status": 0
}

[tobiasschweizer]

Do you plan to include the resources' properties (besides linking properties) as well?

In the old graph view, we had the option to expand a resource's properties to get more information about the instance.

[tobiasschweizer]

für jemanden, dem

the new generation of triplestores will do a grammar check and randomly reject transactions if the found a violation of German grammar

[benjamingeer]

Do you plan to include the resources' properties (besides linking properties) as well?

Lukas and I decided not to do this, for better performance. We can add some JavaScript that opens the resource viewer if you click on a node.

[benjamingeer]

But the request to graph view gives me an empty result

This is because I forgot that link values for standoff links don't have permissions. Fixed.

I also noticed that if you query a node that has no links, you get an empty graph. Fixed this too.

Added tests for both cases.

[tobiasschweizer]

Ok, the query for http://localhost:3333/v1/graphdata/http%3A%2F%2Fdata.knora.org%2Fa-thing-with-text-values works now.

I encounter a strange behavior when opening some resources of type Thing in the GUI. Sometimes the GUI tries to display them as if they were books.

For example in the case of "excluded alpha":

Could this be caused by a change in imagebase.js?

Another thing that attracted my attention is the mouse wheel event in the graph view. I would expect it to make the graph scale but instead it flickers.

[tobiasschweizer]

Could you add a comment here explaining why the Iris are swapped depending on the state of outbound (outgoing or incoming links)?

[benjamingeer]

I opened another issue for the isPartOf problem: #334, and added comments as requested. OK to merge now?