structured-data-extractor

A framework for extracting RDFa, JSON-LD, Microdata and text content from webpages. In general, it relies and uses on RDF4J framework.

(note; this documentation was written 6 years after initial development).

Modules

The project contains the following modules:

• microdata-parser : code for parsing Microdata markup, initialy copied from the Any23 project if I remember.

• extractor-core : this is where the actual extraction happens. The main interface is fr.sparna.rdf.extractor.DataExtractor. There are 4 implementations :

  • fr.sparna.rdf.extractor.jsonld.JsonLDExtractor - this is JSON-LD 1.0 only (remember this was developped in 2018). It relies on RDF4J JSON-LD parser
  • fr.sparna.rdf.extractor.rdfa.RdfaExtractor - this relies on semargl RDFa parser
  • fr.sparna.rdf.extractor.microdata.MicrodataExtractor - this relies on the microdata-parser module
  • fr.sparna.rdf.extractor.content.ContentExtractor - this one extracts the actual text of the page, removing HTML markup etc, trying to remove menus, etc. This is relying on the boilerpipe library. This is not useful for the ELI project and was developped for other purposes.

  In addition, the resulting triples are being filtered and post-processed by a bunch of filters inside the fr.sparna.rdf.handler package

• extractor-cli : a command-line interface to run the extractor, coupled with a simple crawler implementation. The idea is to crawl a set of webpages, and pass each webpage content to the extractor.
• extractor-server : the encapsulation of the extractor in an API (e.g. something like curl --header "Accept: application/ld+json" http://localhost:8080/extractor-server/api/v1/extract?uri=http://sparna.fr). The idea is that this server can connect to an underlying RDF repository, storing the resulting triples in named graphs.

How to run the command-line interface

• Try java -jar extractor-cli-onejar-{version}-onejar.jar --help tp get the help message
• There are 2 commands :
  • crawl
  • list
• crawl was an attempt to run free-form crawler, relying on Crawler4J, with additionnal deciderules taken from Heritrix. The main class is fr.sparna.rdf.extractor.cli.crawl.ExtractorCrawler. This is really "poor man's crawling" and I don't think this should be reused; more rebust crawlers should be used for free crawling
• processList is simply reading a text file containing one URL per line, and applies the extraction to each of those URLs one by one. This was originally applied on list of ELI URIs sent by the Member States.

Here is a complete command-line example:

java -Xms512M -Xmx2048M -jar extractor-cli-1.0-SNAPSHOT-onejar.jar list \ --input random-elis-test.txt \ --output output \ --exclude processed-urls.log \ --namespaces eli,http://data.europa.eu/eli/ontology# xsd,http://www.w3.org/2001/XMLSchema# ev,http://eurovoc.europa.eu/ corp,http://publications.europa.eu/resource/authority/corporate-body/ lang,http://publications.europa.eu/resource/authority/language/ m-app,http://www.iana.org/assignments/media-types/application/ res-oj,http://publications.europa.eu/resource/oj/ res-celex,http://publications.europa.eu/resource/celex/

The file random-elis-test.txt contains the following URIs:

http://data.europa.eu/eli/reg/2003/20/oj
http://data.europa.eu/eli/reg/2002/41/oj
http://data.europa.eu/eli/dec/2002/95/oj
http://data.europa.eu/eli/dir/1998/91/oj
http://data.europa.eu/eli/dec/1983/59/oj
http://data.europa.eu/eli/reg/2002/43/oj
http://data.europa.eu/eli/dir/2001/5/oj
http://data.europa.eu/eli/dec/1982/39/oj
http://data.europa.eu/eli/dir/1997/53/oj

Note : somehow (I can't remember where exactly) the successfully processed URLs are logged into processed-urls.log, so that if the process fails for any reason, this file is being passed back to the second run and URLs already processed are not extracted a second time.

The folder under extractor-cli/src/test/resources/URI-lists contains the files of the URI lists that were used to extract dataset from Portugal, Eur-Lex, Ireland, Denmark and Italy, for the 2018 Datathon. The resulting datasets were published on the EU ODP, see https://data.europa.eu/data/datasets?locale=en&minScoring=0&query=ELI&page=1

Note on the storage in the triplestore

The extractor-server modules persists the result of the extraction in a triplestore. Each set of triples from each page is kept in a separate named graph. The named graph is identified by the original URL of the page, and is described with a dcterms:modified triple with the date of insertion, and a dcterms:isPartOf triple with the domain name of the page. This is useful to e.g. select or delete or query all named graphs coming from a known domain/website. See the class fr.sparna.rdf.extractor.RepositoryManagementListener that is responsible for this.

How this project could be reused for ELI-based search ?

• part of the module extractor-core could be reused, with only RDFa and JSON-LD extractors. JSON-LD extractor would need to be upgraded to JSON-LD 1.1. The code is well documented and - I think - rather robust.
• you may want to run that extraction service as a Microservice, so extractor-server could be useful too.