1. A system, comprising: at least one non-transitory computer-readable medium having stored therein computer-executable components; and at least one processor that executes the following computer-executable components stored on the at least one non-transitory computer readable medium: a parameter separation component configured to: determine a plurality of tool parameters that impact a tool performance indicator associated with a tool in a semiconductor fabrication system; and for each tool parameter of the tool parameters, generate a distinct function that characterizes a behavior of the tool performance indicator in terms of the tool parameter; a quality scoring component configured to determine respective quality scores for the functions, wherein a quality score indicates how closely the associated function predicts an actual value far the tool performance indicator; a sensitivity component configured to determine respective sensitivity scores for the functions, wherein a sensitivity score is a measure of sensitivity of the tool performance indicator to changes in values of the tool parameter associated with the function, and wherein the sensitivity component, based on identification of an upper operating limit and a lower operating limit for at least one tool parameter associated with at least one function, only employs a portion of a differential curve for the at least one tool parameter between the upper operating limit and the lower operating limit to determine at least one sensitivity score for the at least one function; a ranking component configured to generate respective composite scores for the functions, wherein a composite score for the function comprises the quality score for the function weighted by a weighting factor based on the sensitivity score for the function; a filtering component configured to identify a subset of the tool parameters having a defined impact on the tool performance indicator based on the respective composite scores; and an interface component configured to provide, to a real-time early warning system, an output that initiates the real-time early warning system to generate a preventative maintenance warning based on the output, wherein the preventative maintenance warning comprises guidance on a maintenance effort on which to focus for keeping the tool performance indicator within a desired operating limit based on the subset of the tool parameters.