1. A pattern recognition system comprising: (a) input means for receiving feature values of an unknown object, wherein the object belongs to one of a plurality of models, and wherein each feature value has a known range; and (b) constraint means for providing a network of constraints representing one of the plurality of models, the constraint means comprising a plurality of weights, a plurality of nodes and a plurality of layers wherein each layer of nodes corresponds to a particular feature and each node is associated with a sub-range of the typical values for that feature for a selected one of the plurality of models, and wherein each weight corresponds to a value representing a relationship between the nodes of at least one feature type and the selected model, the constraint means performing the steps of: (c) receiving the features from the input means; and (d) responsive to the relationship between those nodes that correspond to the feature values and the weights between those nodes, generating a value corresponding to the confidence that the object belongs to the selected model.