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Morph-Skyline++ is an RDB2RDF engine for queries based on qualitative preferences, developed by the Ontology Engineering Group, that follows the R2RML specification (

Qualitative preferences [1] allow a user to express preferences comparatively over a set of alternatives. They are more intuitive and easier to elicit from the user. For example, it is more natural for users to express phrases such as "I prefer A more than B" (prioritized preferences), "If X, I prefer A to B" (conditional preferences), "I prefer X if there is no other Y with a lower A and a higher B" (skyline). These phrases can be modeled with qualitative preferences.

Morph-Skyline++ extends Morph-RDB and it supports two operational modes: data upgrade (generating RDF instances from data in a relational database) and skyline query translation (SPARQL to SQL). Morph-Skyline has been tested on TPC-H benchmark and LinkedMDB. At the moment, Morph-Skyline++ works with EXASol.

This repository contains code and experiments for the paper "Morph-Skyline++: A Virtual Ontology-Based Data Access Approach for Qualitative Queries". Experiments can be found in the Experiments directory of this repository.

User guides: As Morph-Skyline++ extends Morph-RDB, for those who want to use this project on an user level, you can find a little guide for Morph-RDB to on the main branch wiki :

If, on the other hand, you want to edit the project or at least work from an IDE such as Eclipse, we suggest you to follow this steps:

  • Download the source code.
  • Once unziped, you may notice that the imports doesn´t match the actual directories. In order to avoid changing all the imports or all the directories, import this way: Import -> Maven -> Existing Maven Project, and select as root the folder where you unziped the project (it may take a few minutes).
  • Now that it´s finally imported, you can run the file (in other to pass the arguments in Eclipse, right click, Run As -> Run Configuration -> Arguments, and remember to imput both the path to the .properties file and it´s full name).
  • In case the program doesn´t find the file, move it from "morph-examples" to "morph-r2rml-rdb", thought this file isn´t essential.

References: [1] Patel-Schneider, P. F., Polleres, A., & Martin, D. (2018, November). Comparative preferences in SPARQL. In European Knowledge Acquisition Workshop (pp. 289-305). Springer, Cham.


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