SQL Parsing Error Question

I am starting a project which will be using PC workstations connected to an Informix database running on a UNIX box. (I have never worked with Informix before.) I need to develop a client application that will allow users to add change and delete SQL logical expressions that will be stored in a database and later retrieved by processes to construct "WHERE" clauses in SQL statements. The reason for this is to allow the users to dynamically change business rules in the system. My question is, what is the best way to verify these logical expressions are syntactically correct before storing them in the database? I am considering building a "dummy" SQL statement, executing it against a dummy table, and checking for an execution error. My concern is how can I get a meaningful error message to present to the user if the expression contains errors? I am considering using VB to develop the client application. Any suggestions? Please email me at raron@cyberramp.net