1. A method of evaluating differences in parameters for one or more computer systems comprising: a processor obtaining from a data storage device, a first data set pertaining to a plurality of parameters of a first computer system and obtaining from said data storage device, a second data set pertaining to said plurality of parameters for a second computer system to permit comparison of corresponding parameters for said computer systems by comparing each parameter in said first data set to the corresponding parameter in said second data set, wherein said first and second computer systems can be different systems or a same system at different times; said processor referencing one or more differential rule definitions for selecting one or more particular parameters to be evaluated, said rule definitions including weights indicative of relative importance of differences in said particular parameters as they relate to operation of said systems, one or more of said rule definitions including one or more suppression flags to model dependencies between rule definitions to control whether a particular rule definition is executed based on the result of execution of one or more dependent rule definitions; for each rule definition, subject to said dependencies derived from said suppression flags, said processor: i. comparing values for said particular parameters in said first data set to corresponding values for said particular parameters in said second data set; ii. from said comparing, said processor determining if differences exist between said corresponding values in said data sets; iii. if said differences exist, said processor determining weights corresponding to said particular parameters from said rule definition, said weights being indicative of the relative importance of said differences for said particular parameters; and said processor using weights determined for any differences in said plurality of parameters to generate an evaluation of said computer systems against one another.