A structured history for command recall

A history function provides users with access to previously used commands. However, existing history functions are very limited in usability. Two different models and implementations of a structured history function were explored and contrasted. A structured history is based on a mental model of users´ interaction with a system. This tool consists of a database of commands previously executed by a user, together with methods for storing and recalling these commands. In the first model all commands are stored, eliminating duplicates and short commands. Retrieval is by pattern matching of several different types, frequency, and time. The second model is a parallel distributed processing (PDP) model that presents the user with a list of likely candidates for good matches to an input string. The PDP history allows for misspellings and retrieves a list of related commands