The Bernoulli-Euler Online project (BEOL) aims to integrate different editions, consisting of the writings of members of the Bernoulli dynasty and Leonhard Euler, into one platform. At the current stage of the project, we have have been able to include several hundred letters exchanged between mathematicians of the early modern period. The data is stored in an RDF triplestore and accessed via the Knora API, using JSON-LD as the exchange format. Knora is a generic framework and is further extended for the special needs of the BEOL project. BEOL defines its own OWL ontologies that are derived from the more generic Knora ontologies.
In our contribution, we present the BEOL project, which can be accessed through our graphical user interface, SALSAH, which is based on Angular 4. It displays the letters and the relations to their authors, recipients, and mentioned persons, as well as to other letters or bibliographical items, along with a subject index. The letters' transcriptions often include mathematical notation (in LaTeX format), which is rendered using MathJax. Whenever available, high-quality facsimiles are displayed with the transcriptions, relying on the IIIF standard.
To use the full power of RDF, we developed a flexible way of querying RDF data that is similar to a SPARQL endpoint, but serves the data via the Knora API as JSON-LD. We call it the Knora Query Language (KnarQL). When the user enters search criteria, SALSAH generates a KnarQL query requesting a subgraph of the BEOL graph, which is then returned by the API and displayed within SALSAH.
Like Knora, SALSAH is developed in a generic way. The functionality developed for the BEOL corpus can be applied to other projects as well. Rather than dealing with predefined routes on the server and custom response formats, we are developing SALSAH in such a way that it can deal with complex linked data serialised as JSON-LD.