Apparatus and methods facilitate customizable and extensible performance monitoring of a computer network. One method accepts a composite score definition in terms of N system variables, wherein N2; determines N raw data values, each raw data value corresponding to one of the N system variables; computes the composite score in accordance with the definition using the N raw data values as inputs; and outputs the composite score. The composite score definition is preferably in the form of a markup language, such as XML. The composite score definition preferably comprises, for each of the N system variables, a mapping and a weight. Preferably the composite score is displayed in at least one graphic form, such as a dial gauge, a bar indicator or a number, on a hypertext page. The hypertext page preferably contains one or more links to hypertext pages containing information regarding the scores and/or raw data values from which the composite score is derived. Another method accepts a mapping by which a raw data value associated with a corresponding system variable is mapped to a score, determines a raw data value corresponding to the system variable, converts the raw data value to a score in accordance with the mapping; and produces an output based on the score. One apparatus comprises a composite score definition, a data collector, a calculation logic and an output. The data collector collects a raw data value corresponding to one of the N system variables. The calculation logic is connected to the data collector and calculates the composite score in accordance with the definition using the N raw data values as inputs. The composite score is conveyed by way of the output. Preferably, the data collector comprises a database in which at least some of the raw data values are stored and a communication module by which at least some of the raw data values are transported, preferably according to the SNMP and/or the ICMP protocols. Another apparatus comprises a mapping, a data collector, a converter and an output. A raw data value associated with a corresponding system variable is mapped to a score, according to the mapping.