ChangeLog for ARQ
=================

ARQ 2.0
-------

This version uses the SPARQL algebra directly,
then produces an execution scheme that uses streaming
execution where possible.

+ Multiple query engines:
  + Main query engine for optimization and efficient execution
  + Reference engine for checking functionality
    (implements the SPARQL evaluation semantics very simply for clarity and validation)
  + Remote access engine for querying SPARQL endpoints over HTTP.
  + Engine1, for exact ARQ1 semantics and enhancements
    (deprecated for new applications (and will be removed sometime))
  + RDQL engine
  + See also SDB - an ARQ query engine that for RDF stored in SQL databases 

+ Access and extension points:
   + Filter functions
   + Property functions
   + The parsed syntax
   + Generation of the SPARQL algebra expression
     + Modification of SPARQL algebra expression before executin plan generation
     + Custom algebra operations 
   + Basic graph pattern replacement or modification
     for access to other data sources
   + Modular query engine class hierarchy for reuse of machinary,
     resulting in less extra coding for extensions.
 
 + Internal changes
   + Package reorganisation
     Implemnentation in com.hp.hpl.jena.sparql
   + Filter functions now take a Context, not an ExecutionContext.
   + Deprecate "EXT" form from ARQ.
     (Property functions are better)