Interactive systems, such as editors and program development environments, should explicitly support facilities that permit a user to reverse the effects of past actions and to restore an object to a prior state. A model for interactive systems that allows such recovery facilities to be defined precisely and user and system responsibilities to be delineated is presented. Various techniques for implementing recovery are described. Application of a general recovery facility to support reverse execution is discussed. A program development system (called COPE} with extensive recovery facilities, including reverse execution, is described.

this paper, we propose a general framework for implementing undo in collaborative systems. The framework allows users to individually reverse their own changes, taking into account the possibility of conflicts between different users' operations that may prevent an undo. The proposed framework has been incorporated into DistEdit, a toolkit for building group text-editors. Based on our experience with DistEdit's undo facilities, we discuss several issues that need to be taken into account in using the framework, in order to ensure that a reasonable undo behavior is provided to users. We show that the framework is also applicable to single-user systems, since the operations to undo can be selected not just on the basis of who performed them, but by any appropriate criterion, such as the document region in which the operations occurred or the time interval in which the operations were carried out. Categories and Subject Descriptors: D.2.2 [Software Engineering]: Tools and Techniques -- User Interfaces; H.1.2 [Models and Principles]: User/Machine Systems -- Human Factors; H.2.2 [Database

The ability to undo operations is a standard feature in most single-user interactive applications. However, most current collaborative applications that allow several users to work simultaneously on a shared document lack undo capabilities; those which provide undo generally provide only a global undo, in which the last change made by anyone to a document is undone, rather than allowing users to individually reverse their own changes. In this paper, we propose a general framework for undoing actions in collaborative systems. The framework takes into account the possibility of conflicts between different users' actions that may prevent a normal undo. The framework also allows selection of actions to undo based on who performed them, where they occurred, or any other appropriate criterion. The proposed framework have been incorporated in DistEdit, a toolkit for building text group editors. Based on our experience, we discuss methods for maintaining the undo information in a groupware env...

An undo facility is an essential component of most interactive applications. In current operating system shells, whether textual or graphical, such facilities are typically very poor. Algorithms are presented for adding a recovery mechanism to a shell which allows previous commands to be selectively undone and redone, and previous versions of files to be recovered. The recovery mechanism involves making the shell control resources in a more intelligent way. Programs are run under greater control, with the shell monitoring and analysing their resource requests. This provides better high level information to the shell and, for example, provides techniques to prevent foreign or untrustworthy programs from doing any damage, and to reduce problems with conflicting resource requests from concurrent programs. A prototype implementation has been implemented to investigate the convenience and natural feel of these facilities. 1 Introduction A recovery ability is a crucial feature that many int...

Success and failure of programming environments 1 Success and failure of programming environments- Report on the design and use of a graphic abstract syntax tree editor-

language-based editor (LBE) that knows the syntactic and semantic rules of Pascal. It is the first step in development of a comprehensive Pascal program development environment. Poe's design began in 1979; version 1 is currently operational on Vax lls under Berkeley Unix and on HP 9800-series personal workstations. Poe is writ. ten in Pascal, and is designed to be readily transportable to new machines. An editor-generating system called Poegen is operational, and much of the language-specific character of Poe is tabledriven and retargetable. Poe was inspired in large measure by the Cornell