Editor’s Note: This is the second of four blog posts detailing our Google Summer of Code 2013 students’ work. I edited it to include a very incomplete list of public RDF repositories. —John Woods

Introduction

Across all fields and disciplines, contemporary scientists are faced with a massive and growing volume of data. It often won’t fit in a lab notebook, and there is a pressing need to share it more quickly and widely than publication in a journal article would allow for. Database software is one great solution for storage of such data, but relational databases become brittle in the face of changes or new information, do not play nicely with other databases or data derived from such databases, and may not be fully machine (or human) readable without pre-existing knowledge.

Meanwhile, the Internet is an extremely useful place to discover and share useful information, but it is essentially built around linked documents, rather than pure data, and so our primary mechanism for sharing data is as HTML or text.

RDF and related technologies propose to provide the means to move beyond a web of documents to a web of data. Along the way, these technologies may address many of the problems with conventional relational databases (e.g., SQL). At its core, RDF defines an extremely flexible method for representing data on the web — which is nonetheless unambiguously defined, without any external context, and can be linked to other data as web documents link to each other. Because RDF data can be understood as either a set of subject–predicate–object statements or a directed graph with labeled edges, a number of supporting standards and tools that have grown up around it to provide powerful storage and access methods that are often easier to implement and use than those associated with relational databases and the document-based web.

Enter PubliSci

This summer I created a Ruby gem, PubliSci, to facilitate data publication and interaction using the Semantic Web. The format offers a unified way to share and combine information from multiple sources, support for machine learning tools, a flexible query language that makes application integration easy, and the backing of the World Wide Web Consortium (W3C) and other standards-setting bodies.

The PubliSci gem comprises a set of parsers for converting various input formats using the RDF Data Cube vocabulary, and a Ruby interface for defining new ones. Since the relationship between external datasets and semantic web formats is sometimes up to interpretation, a domain-specific language is included to allow end users to resolve ambiguities and provide additional metadata.

Along with the conversion tool, a standalone server is available as an extension to the gem that simplifies setting up and interacting with RDF data stores. The server allows import, export, querying, and management of external triplestores such as 4store, and supports both cross-domain access and content negotiation so the gem can be accessed using Javascript or other applications.

Triplestores are databases for the storage and retrieval of triples, which are typically subject–object–predicate relationships (e.g., Bob knows Fred).

If you’d like to contribute, the source code is available on Github, and a broad outline of the to do list can be had as well.

Usage

Once you’ve done gem install publisci , you can require the gem in the normal way ( require 'publisci' ). To invoke the domain-specific language, you’ll also want to include the DSL module:

require 'publisci' include PubliSci::DSL

Input data can be specified like so:

# Specify input data data do # Use local or remote paths to point to the data file you want to load: source 'https://github.com/wstrinz/publisci/raw/master/spec/csv/bacon.csv' # Specify datacube properties. dimension 'producer', 'pricerange' measure 'chunkiness' # Set parser-specific options. option 'label_column', 'producer' end

You can provide meta-data on your dataset as well.

metadata do dataset 'bacon' title 'Bacon dataset' creator 'Will Strinz' description 'some data about bacon' date '1-10-2010' end

Sending the data to a repository is simple.

# Send output to an RDF::Repository # can also use 'generate_n3' to output a turtle string repo = to_repository

SPARQL queries can be run on the dataset using the QueryHelper module.

# run SPARQL queries on the dataset PubliSci::QueryHelper.execute('select * where {?s ?p ?o} limit 5', repo)

Finally, data can be exported in other formats, such as ARFF:

# export in other formats PubliSci::Writers::ARFF.new.from_store(repo)

Some places to look for RDF repositories