An Implementation of View Updates 
(Using a Language of Bidirectional Transformations) 


This is an implementation of the frontend of a relational database: it
includes an SQL parser and a (partial) translation from SQL into the lens
language used to manipulate data internally.  (See the accompanying report for
more details.)  There is no query optimization or persistence (and thus no
buffer pool management, concurrency control, etc.).  It supports many queries
and updates on single relations, and contains partial support for updates of
equijoins using primary keys.


STATUS

The lenses used to implement the supported subset of SQL are complete.
However, there are a number of problems with the presentation code.  While
relations are represented as labeled trees, they are presented to users in the
typical rows-and-columns fashion.  This presentation currently makes some
assumptions about the forms of trees used internally.  Moreover, the code that
executes updates also requires that the internal trees conform to a number of
specifications (e.g. the ordering of children for certain nodes).  These
constraints became more and more difficult to maintain toward the end of the
project, and (unfortunately) this code is in desperate need of a redesign.


RUNNING

This implementation was built using Standard ML of New Jersey (Version
110.0.7), but should run with any implementation of Standard ML.  The Loop
structure (see loop-sig.sml and loop.sml) contains the main user interface.
If you'd like to run the code, look there first.  One note to those brave
enough to run the code: the SQL parser expects all SQL keywords to be lower
case.  See the examples in the sql/ directory for the sorts of things the
parser will accept.


BUGS

There are number of other aspects of the implementation that are incomplete.
They are marked "FIXME" in the source.


ACKNOWLEDGMENTS

Thanks to Benjamin Pierce, Alan Schmitt, Michael Greenwald, and Jonathan Moore
whose work this implementation is based on.  Also, thanks to Chris Okasaki,
Robert Harper, Tom Murphy VII, and Kevin Watkins whose parser code is included
with this implementation.  Special thanks to Tom7 who took the time to answer
my questions about the parser.


Daniel Spoonhower
spoons+@cs.cmu.edu
3 May 2004