[nendroid]

Some detail here. What goes on in relational algebra is that the FROMCLAUSE is encoded into an axiomatic primitive called a RELATION and you get stuff like this:

   SELECTCLAUSE(WHERECLAUSE(relation)) = relation
   WHERECLAUSE(SELECTCLAUSE(relation)) = relation

Basically every operation in relational algebra produces a primitive of type RELATION which allows for all operations to be composed like unix pipes.

My example in the previous post has a flaw where it's not clear what:

   SELECTCLAUSE * WHERECLAUSE = ????

will output because there's no meaning to a SQLEXPRESSION without a FROMCLAUSE. But hopefully it illustrates the point. I'm putting this here for anyone who's nitpicky about the details. The relational algebra syntax is much more elegant.