*Squirrel* uses information obtained during a successful parse of
a question to produce a formal representation of its meaning expressed
in *Property Theory*. This expression is then translated through
the following representations and optimisations to produce the final
SQL query.

- Property Theory (PT).
- First order logic (FOL).
- Untyped Relational Calculus (URC).
- Domain Relational Calculus (DRC).
- First Optimisation (OP1).
- Tuple Relational Calculus (TRC).
- Second Optimisation (OP2).
- Third Optimisation (OP3).
- SQL.

The query becomes database specific when it is mapped from the
*First Order Logic* to the *Untyped Relational
Calculus*. It is at this point that information in the the *Extended Data Model* (EDM)
is used to relate semantic constructions derived from the query with
the kinds of relations available in the database.

- Property Theory (PT)
- First order logic (FOL)
- Untyped Relational Calculus (URC)
- Domain Relational Calculus (DRC)
- First Optimisation (OP1)
- Tuple Relational Calculus (TRC)
- Second Optimisation (OP2)
- Third Optimisation (OP3)
- SQL

Chris Fox, September 1995