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README.md

README.md

Hedgehog RDF Publisher

By Ashley Smith and Christopher Gutteridge, University of Southampton

http://data.southampton.ac.uk/

Hedgehog is a system for publishing datasets in RDF. The core system runs scripts (known as 'quills') which pull data from a source and expose the data as RDF triples. It then performs a set of tasks on those triples. Examples include

  • Converting the data to RDF documents in various formats, such as Turtle
  • Automatically adding meta-data about the data, including provenance
  • Importing the triples into a triplestore such as 4store
  • Uploading the data documents to a server for publishing on the web

License

This work is released under the GNU General Public License version 2.0 http://www.gnu.org/licenses/gpl-2.0.html

General Documentation

How to run Hedgehog

Hedgehog normally runs via crontab. Active quills can be run on a regular basis based on their needs, typically once a day but occasionally more or less often.

To run hedgehog with a specific quill:

publish_dataset <quill_name_here> [<options>]

Options are:

  • --log Logs to a log file, rather than STDOUT
  • --force Ignores hash check, always publishes
  • --republish Doesn't run quill, looks for a previous successful publish and simply re-imports this

Quills

A Quill has a publish.json file which is the entry point and only mandatory element. It can also contain other files and scripts which are necessary to acquire and/or process the data into the correct format.

  • The first thing Hedgehog does is creates a new temporary directory and copies all of the files from the Quill directory into that directory.
  • It then goes to the Download section of the quill publish.json and performs all download steps specified.
  • It then goes to the tools section of the quill publish.json and copies any required tools from the Hedgehog tools directory into the temporary directory.
  • It then copies any files listed in the "incoming" section from the incoming directory (specified within the config of Hedgehog itself) into the temporary directory.
  • It then runs any commands in the commands > prepare section on the command line.
  • (Optional) It then compares the dataset files with the hashes of the previously processed dataset, and if it determines that the datasets are identical to the last known versions then it stops here. Whether this happens or not is usually specified in the publish.json file, but may be overridden with the command line switch --force.
  • Otherwise it moves on to the import section of the commands section.
  • After the import section is complete, Hedgehog does some processing which is specified globally by Hedgehog and is independent of the Quill.
  • Finally the commands in the completed section of the commands section are executed.