London Lucene/Solr Meetup – Relevance tuning for Elsevier’s Datasearch & harvesting data from PDFs

Elsevier were our kind hosts for the latest London Lucene/Solr Meetup and also provided the first speaker, Peter Cotroneo. Peter spoke about their DataSearch project, a search engine for scientific data. After describing how most other data search engines only index and rank results using metadata, Peter showed how Elsevier’s product indexes the data itself and also provides detailed previews. DataSearch uses Apache NiFi to connect to the source repositories, Amazon S3 for asset storage, Apache Spark to pre-process the data and Apache Solr for search. This is a huge project with many millions of items indexed.

Relevance is a major concern for this kind of system and Elsevier have developed many strategies for relevance tuning. Features such as highlighting and auto-suggest are used, lemmatisation rather than stemming (with scientific data, stemming can cause issues such as turning ‘Age’ into ‘Ag’ – the chemical symbol for silver) and a custom rescoring algorithm that can be used to promote up to 3 data results to the top of the list if deemed particularly relevant. Elsevier use both search logs and test queries generated by subject matter experts to feed into a custom-built judgement tool – which they are hoping to open source at some point (this would be a great complement to Quepid for test-based relevance tuning)

Peter also described a strategy for automatic optimization of the many query parameters available in Solr, using machine learning, based on some ideas first proposed by Simon Hughes of dice.com. Elsevier have also developed a Phrase Service API, which helps improve phrase based search over the standard un-ordered ‘bag of words’ model by recognising acronyms, chemical formulae, species, geolocations and more, expanding the original phrase based on these terms and then boosting them using Solr’s query parameters. He also mentioned a ‘push API’ available for data providers to push data directly into DataSearch. This was a necessarily brief dive into what is obviously a highly complex and powerful search engine built by Elsevier using many cutting-edge ideas.

Our next speaker, Michael Hardwick of Elite Software, talked about how textual data is stored in PDF files and the implications for extracting this data for search applications. In an engaging (and at some times slightly horrifying) talk he showed how PDFs effectively contain instructions for ‘painting’ characters onto the page and how certain essential text items such as spaces may not be stored at all. He demonstrated how fonts are stored within the PDF itself, how character encodings may be deliberately incorrect to prevent copy-and-paste operations and in general how very little if any semantic information is available. Using newspaper content as an example he showed how reading order is often difficult to extract as the PDF layout is a combination of the text from the original author and how it has been laid out on the page by an editor – so the headline may be have been added after the article text, which itself may have been split up into sections.

Tables in PDFs were described as a particular issue when attempting to extract numerical data for re-use – the data order may not be in the same order as it appears, for example if only part of a table is updated each week a regular publication appears. With PDF files sometimes compressed and encrypted the task of data extraction can become even more difficult. Michael laid out the choices available to those wanting to extract data: optical character recognition, a potentially very expensive Adobe API (that only gives the same quality of output as copy-and-paste), custom code as developed by his company and finally manual retyping, the latter being surprisingly common.

Thanks to both our speakers and our hosts Elsevier – we’re planning another Meetup soon, hopefully in mid to late June.

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