PQL/Java: A powerful and easy-to-use declarative parallel query language for Java

Joint work with Yannis Smaragdakis, Neil Immerman, and Hilmar Ackermann.

The popularisation of parallelism is arguably the most fundamental computing challenge for years to come. We present an approach where parallel programming takes place in a restricted (sub-Turing-complete), logic-based declarative language, embedded in Java. Our logic-based language, PQL, can express the parallel elements of a computing task, while regular Java code captures sequential elements. This approach offers a key property: the purely declarative nature of the language allows for aggressive optimization, in much the same way that relational queries are optimized by a database engine. At the same time, declarative queries can operate on plain Java data, extending patterns such as map-reduce to arbitrary levels of nesting and composition complexity.

Implementation and updated language specification with full domain inference specification will be released soon.

The language

PQL language definition (draft)
Intermediate language specification
Implementation (on bitbucket.org):

pqlib: intermediate representation and optimisation library
pql-compiler: compiler frontend
Build instructions:
- mkdir lib
- Install asm-4.1-bin.zip from here. Copy all jar files from asm-4.1/lib/ to lib/.
- Install JUnit 4.0 from here. Copy the jar file (junit-4.0.jar) to lib/.
- git clone https://bitbucket.org/creichen/pqlib.git
- cd pqlib; make jar; cd ..
- git clone https://bitbucket.org/creichen/pql-compiler.git
- cd pql-compiler; make
- The compiler should now be built, as ./dist/bootstrap/bin/javac. Remember that you need to link against pqlib.jar to execute compiled PQL programs.
- There are a number of known issues with the compiler as-is, but feel free to file additional bugs or send in patches!

Publications

Hilmar Ackermann, Christoph Reichenbach, Christian Müller, Yannis Smaragdakis: A Backend Extension Mechanism for PQL/Java with Free Run-Time Optimisation. In Compiler Construction 2015. [pdf]
Hilmar Ackermann: Dynamische Übersetzung von PQL in Java-Bytecode (2013), B.Sc. thesis, Johann-Wolfgang Goethe University Frankfurt. [pdf, German]
Christoph Reichenbach, Yannis Smaragdakis, Neil Immerman: PQL: A Purely-Declarative Java Extension for Parallel Programming
In 26th European Conference on Object-Oriented Programming (ECOOP) (2012). [pdf] [slides]