Abstract: Methods and systems for determining which groups of instructions are to be executed when a specific symbol patterns has been detected. A prefetch block receives an identification of the symbol pattern detected. The prefetch block then retrieves the groups of instructions which relate to that particular symbol pattern. These are passed to an execution block that retrieves state information for each user defined rule from which the groups of instructions originate. The execution block then checks, for each group of instructions, the state information. If the state information indicates that a particular group of instructions can be executed, the execution block executes that group.