1. A computer-implemented method for monitoring a component or system of an aircraft or spacecraft, comprising: generating an optimized decision tree, using the computer, nodes of which contain attributes of a respective input vector, leaves of which each contains a classification function and associated connections of which between the nodes of the decision tree are weighted; providing the input vector which is derived from a data signal received from a sensor that monitors the component or system of the aircraft or spacecraft; storing the data signal received from the sensor in a memory for subsequent retrieval for evaluation; implementing a condition monitoring, using the computer, based on the evaluation of the data signal stored in the memory, in which a condition of the component or system is determined using the weighted decision tree and on the basis of the attributes of the input vector, in that an item of information concerning which of the classification functions of the decision tree best corresponds to the input vector based on the weighted decision tree, is calculated and output; calculating, using the computer, a probability of an applicability of the corresponding classification function for each leaf of the weighted decision tree; and delivering, using the computer, a result stating the probability at an output of the weighted decision tree that corresponds to the leaf of the weighted decision tree, wherein the data signal is determined by at least one of a continuous-time and discrete-time measurement of a physical variable at the component or system.