Embodiments of the invention include a data processing system and method for processing data in a mediation or service provisioning system of a communications network. In the invention, a special logic definition structure is formed based on the processing logic. The logic definition structure is designed so that it is easy to modify and efficient to execute. This is made possible by defining the processing logic in the form of a series of byte code instructions, wherein each instruction contains a pointer to a piece of program code performing a function and a pointer to parameters to be used in performing the function. The instructions, the program codes performing the functions, the pointers and the data under processing are preferably stored in arrays thus allowing the use of efficient pointer mechanisms together with flexibility and ease of modification.