This module installs a Jupyter kernel for SPARQL. It allows sending queries to an SPARQL endpoint and fetching & presenting the results in a notebook.

It is implemented as a Jupyter wrapper kernel, by using the Python SPARQLWrapper & rdflib packages.

The kernel has only been tried with Jupyter 4.x. It works with Python 2.7 and Python 3 (tested with Python 3.4).

The above mentioned SPARQLWrapper & rdflib are required dependencies (they are marked as such, so they will automatically be installed with the package if needed).

An optional dependency is Graphviz, needed to create diagrams for RDF result graphs (Graphviz's dot program must be available for that to work).

You will need Jupyter >= 4.0. The module is installable via pip.

The installation process requires two steps:

1. Install the Python package:

   pip install sparqlkernel
   

2. Install the kernel into Jupyter:

   jupyter sparqlkernel install [--user] [--logdir <dir>]
   

The --user option will install the kernel in the current user's personal config, while the generic command will install it as a global kernel (but needs write permissions in the system directories).

Additionally, the --logdir <dir> option will define the default directory to use for logfiles (it can be overriden when executing the kernel by defining the LOGDIR environment variable).

Note that kernel installation also installs some custom CSS and a modification for a Pygments highlighter; its purpose is to improve the layout of the kernel results as they are presented in the notebook and to improve conversion to other formats (HTML). But it also means that the rendered notebook will look slightly different in a Jupyter deployment in which the kernel has not been installed, or within an online viewer.

The examples subdirectory contains some notebook examples (again, they will look slightly different if viewed on a running kernel). They can also be viewed through the online Notebook viewer.

To uninstall, perform the inverse operations (in reverse order), to uninstall the kernel from Jupyter and to remove the Python package:

jupyter sparqlkernel remove
pip uninstall sparqlkernel

The kernel implements the standard SPARQL primitives: SELECT, ASK, DESCRIBE, CONSTRUCT. Once the endpoint is defined (see magics below), just write a SPARQL valid query in a cell and execute it; the query will be sent to the endpoint and the results printed out.

The kernel features keyword autocompletion (TAB key), as well as contextual help (Shift-TAB). This is unfinished work: completion is currently done as isolated SPARQL keywords (no SPARQL syntax context is used) and only a few keywords have contextual help, as of now.

It also installs menu entries in the HELP menu pointing to SPARQL documentation.

The query results are displayed in the notebook as cell results; there are a number of choices for the display format, controlled via magics (see below).

Each SPARQL query is immediately launched, once the results are printed out it is forgotten. Cells are thus completely independent from each other (except for magics, which are persistent).

A number of line magics (lines starting with %) can be used to control the kernel behaviour. These line magics must be placed at the start of the cell, and there can be more than one per cell. Valid combinations are thus:

• a cell with only a SPARQL query,
• a cell consisting only of magics,
• and a cell containing both magics and then a SPARQL query (but after the first SPARQL keyword the cell is assumed to be in SPARQL mode, and line magics will not be recognized as such).

Comment lines (lines starting with #) can be freely interspersed between line magics or SPARQL queries.

Magics also feature autocompletion and contextual help. Furthermore, there is a special magic %lsmagics; when executed on a cell it will output the list of all currently available magics. The same info can be obtained by requesting contextual help (i.e. Shift-TAB) on a line containing only a percent sign.

A few of the most relevant magics are explained in the following sections. The complete set is always available in the notebook, by using the help or autocompletion features.

This magic is special in the sense that it is compulsory: there needs to be an endpoint defined before the first SPARQL query is launched, otherwise the query will fail.

Its syntax is:

%endpoint <url>

and it simply defines the SPARQL endpoint for all subsequent queries. It remains active until superceded by another %endpoint magic.

Sets the data format requested to the SPARQL endpoint:

%format JSON | N3 | default

where default selects a default format depending on the requested SPARQL operation (N3 for DESCRIBE and CONSTRUCT, JSON for SELECT).

Sets the output rendering shape:

%display raw | table [withtypes] | diagram [svg|png] [withliterals]

There are three possible display formats:

• raw outputs the literal text returned by the SPARQL endpoint, in the format that was requested (see %format magic)
• table generates a table with the result. The optional withtypes modifier adds to each column an additional column that shows the data type for each value
• diagram takes the RDF graph returned (makes sense only for N3 result format) and generates an image with a rendering of the graph. For it to work, the dot program from GraphViz must be available in the search path. The modifier selects the image format. Default is SVG, which usually works much better (PNG quality is lower, image size is fixed and cannot contain hyperlinks).