Abstract: A system comprises a structure editor, a structure library, an extractor and a user interface, which are stored in computer memory and create structures for recognizing patterns in computer text. The structure editor via the user interface enables a user to input a text string called a model pattern, and uses previously-created structures such as lexical category structures for parsing the model pattern into default definition items. Each default definition item includes attributes specifying the patterns recognizable by the definition item and relationships with other definition items. The structure editor enables and facilitates user modification of the default definition items by generating attribute choices for user selection and allowing a user to generate a new structure if none of the choices is adequate. The resulting definition items form a new definition of a new structure, which is stored in the structure library.