A summarization system generates summaries from documents. Text structure tags, in conformance with the Text Encoding Initiative (TEI), are inserted into the documents to generate encoded documents. The text structure tags, when associated with portions of the document, identify text types. A text type, such as an argumentative text type, provides meta-information about the associated portion of text. The documents are also encoded, via document type declaration ("DTD") in the eXtensible mark-up language ("XML"), to generate a tree structure that depicts the text types and hierarchical relationships among the text types in the tree structure. The summarization system generates a summary of the documents by extracting portions of the document, associated with the text type tags, using the tree structure in accordance with user input. The summarization system may be used to generate summaries from multiple documents.