This schema implements the specifications of the AML 2.0 draft, section 2.1 to 2.3 Rather than use the usual verbose approach where one would use tags to define expressions in a tree like fashion (see old lattice proposal page 27 for an example or take a look at the mathML specification ) we implemented a scheme allowing for the more natural syntax where one writes the formula directly. This schema will validate the formulas, thus allowing for a check before sending the document to an optics code.