What EXACTLY do I need to purchase and WHY?!?!

We are considering purchasing 4GL/GX to create an interface to our database. The hardware is a Sun SPARC running Solaris 2.2 and SE 4.0. We have existing C programs that will need to return values to the created interface. The question is *which products(s) do I need?* I have conflicting reports from Informix that I need RDS, in addtion to 4GL/GX. Another support rep told me I do not need RDS. Which is true? Another rep kept referring to RDS as 4RGL. Is RDS the same as 4RGL? Why do I need RDS? It is my understanding that 4GL/GX will allow me to do SQL calls directly to the database, so I only need to be concerned with the C progrmas. Does 4GL/GX not take care of the return values to the C programs? Is *this* why I need RDS? What else does RDS do that 4GL/GX does not? Thanks in advance, Andy Andy_Mikesell@mail.amsinc.com