Good Afternoon Khurchan2,
As I understand it, you have a piecewise limit function and you want to test if all measured data points fall under this limit.
There are two parts to this project. The first is database connectivity--saving and retrieving data to and from the database. The second is your data processing.
Rather than thinking of the piecewise limit function as a continuous function (like it seems you may want to), it will probably be easiest to think of it discretely, implementing the processing point-by-point. By doing it this way, you will not be checking for overlap of the plots (think calculus), but simply checking each point to see if it is below the required threshold (think comparison).
As mentioned, the database can be accessed via the Database Connectivity Toolkit. I envision the database being a table (called, say, Antenna_Properties) with 5 columns: Key/Index, Antenna_Type, Range_Low, Range_High, Max_Value. With this setup, you will have a row for every range. The Key/Index will provide the distinct name needed for a database and the Antenna_Type will be duplicated for as many pieces of the piecewise function you have for each antenna. This technique allows antennas to have a different number of ranges. (i.e. In the example you gave, there will be 3 rows for Antenna 1; 400-800, 800-1500, and 1500-2500 Hz.) The database query will need to use joins to put the rows back together to create a coherent output.
