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QL: Object-oriented Queries on Relational Data Avgustinov, Pavel de Moor, Oege Jones, Michael Peyton Schäfer, Max Object orientation Datalog query languages prescriptive typing This paper describes QL, a language for querying complex, potentially recursive data structures. QL compiles to Datalog and runs on a standard relational database, yet it provides familiar-looking object-oriented features such as classes and methods, reinterpreted in logical terms: classes are logical properties describing sets of values, subclassing is implication, and virtual calls are dispatched dynamically by considering the most specific classes containing the receiver. Furthermore, types in QL are prescriptive and actively influence program evaluation rather than just describing it. In combination, these features enable the development of concise queries based on reusable libraries, which are written in a purely declarative style, yet can be efficiently executed even on very large data sets. In particular, we have used QL to implement static analyses for various programming languages, which scale to millions of lines of code. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Pavel Avgustinov and Oege de Moor and Michael Peyton Jones and Max Schäfer 2016 Is Part Of LIPIcs, Volume 56, 30th European Conference on Object-Oriented Programming (ECOOP 2016) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.ECOOP.2016.2 urn:nbn:de:0030-drops-60968 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2016.2 eng https://creativecommons.org/licenses/by/3.0/legalcode