Semantic optimization is posible?

Hello people,

I'm thinking to add a stage before the optimizer and after the parser
with a basic rewriter in order to flatten all nested queries using a
pattern and table statistics, here I also can use assetions the
database have. Another and complementary possibility is that I can
make annotations on the query's data structure so that a later stage
can use the semantic info to either prune the search space or to pick
a specific query execution strategy.
Summarizing, I want to add semantic optimization into the query
processing execution.

I need to hear your opinion and your ideas about this, because I have
to choose between this project about semantic optimization and other
about software analysis. My problem is that I don't know how much
dificult can be to do semantic optimization and to do it well. What is
your opinion about? I have to implement the project in 5 months.

Thank you to all!!