In many messaging systems, message selection filtering involves a significant processing overhead. This includes the parsing and preparing of the message selection filters in readiness for evaluation, as well as the evaluation itself. In systems which involve parsing and prepare processing for expressions that include repeated patterns (such as in many JMS environments), a template-based shortcutting of the conventional processing improves performance. A stored parsing template is used to parse an input sequence such as a received data processing instruction. The parse is used to identify expressions of a first type that can then be implicitly optimized by using a stored evaluation template that is associated with expressions of that type.