Abstract: Techniques are disclosed herein to automatically learn a template that describes a common structure present in documents in a training set. The structure of the template is compared to the structure of the documents (or at least a part of each document) in the training set, one-by-one, and generalized in response to differences between the template and the document to which the template is currently being compared. If the structure of any particular document is considered too dissimilar from the structure of the template, then the template is not modified. Various generalization operators are added to the template to generalize the template. One such generalization operator is an “OR”, which indicates that only one of “n” sub-trees below the “OR” operator in the template is allowed at the corresponding position in a document.