The present mechanism provides a grammar for specifying required prerequisites (e.g., number and type of input parameters) that an object must possess in order for processing to occur on the object. The mechanism allows programmers and non-programmers to easily specify these prerequisites. The prerequisites may be associated directly or indirectly with a data structure. For a direct specification, the data structure comprises a parameter declaration for each expected input parameter. For an indirect specification, the data structure comprises a parameter definition that references an external description, such as in an XML document. The data structure also providing a mechanism that identifies a corresponding parameter within an input source for each expected input parameter based on its declaration. The mechanism further populates each expected input parameter with information associated with the corresponding parameter when the data structure becomes instantiated into an object. The mechanism may be provided by a runtime environment.