In this paper, we present a history-based access-control mechanism that is suitable for mediating accesses from mobile code. The key idea behind history-based access-control is to maintain a selective history of the access requests made by individual programs and to use this history to improve the differentiation between safe and potentially dangerous requests. What a program is allowed to do depends on its own behavior and identity in addition to currently used discriminators like the location it was loaded from or the identity of its author/provider. History-based access-control has the potential to significantly expand the set of programs that can be executed without compromising security or ease of use. We describe the design and implementation of Deeds, a history-based access-control mechanism for Java. Accesscontrol policies for Deeds are written in Java, and can be updated while the programs whose accesses are being mediated are still executing.

The X Window System -- has become widely accepted by many manufacturers. X provides network transparent access to display servers, allowing local and remote client programs to access a user's display. X is used on high performance workstation displays as well as terminals, and client programs run on everything from micro to super computers. This paper describes the tradeoffs and basic design decisions made during the design of X Version 11. We presume familiarity with the paper describing X Version 10. Keywords: X Window System, interactive human-computer interface system, distributed systems. c flDigital Equipment Corporation and Silicon Graphics Computer Systems 1990. All rights reserved. -- The X Window System is a Massachusetts Institute of Technology trademark. This paper will appear in a special issue of Software Practice and Experience. y Digital Equipment Corporation, Cambridge Research Lab, One Kendall Square, Bldg. 700, Cambridge, MA 02139, U.S.A. jg@crl.dec.com z ...

this documentation but makes no expressed or implied warranty of any kind and assumes no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising from the use of information or programs contained herein. Copyright c fl1994, 1995, 1996. Mark J. Kilgard. All rights reserved. All rights reserved. No part of this documentation may be reproduced, in any form or by any means, without permission in writing from the author. CONTENTS i

Abstract- The Internet-based desktop environment as defined in this paper consists of a cross-platform browser, a number of server icons (host nodes), a number of application icons (program nodes) and a number of data iwns’(file nodes). In contrast to typical desktops of today, where data icons may be dragged and dropped onto application icons for execution, this environment allows (I) user-defined and reconfigurable execution sequences by creating dependency edges between program nodes (application icons) and file nodes (data icons); (2) data-dependent execution sequences by dynamic scheduling of path as well as loop executions; (3) host-transparency as to the location of applications and data (60th can reside on any host with a unique IP address). We argue that the Internet-based workflow paradigm is suitable for creation of dynamically reco;lfigurable desktop en-vironments. demonstrates The summary of 450 Internet-based expen’ments (1) the value of making the desktop recordable, and (2) the feasibility of rendering it collaborative.

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The Internet-based desktop environment as defined in this paper consists of a cross-platform browser, a number of server icons (host nodes), a number of application icons (program nodes) and a number of data icons (file nodes). In contrast to typical desktops of today, where data icons may be dragged and dropped onto application icons for execution, this environment allows (1) user-defined and reconfigurable execution sequences by creating dependency edges between program nodes (application icons) and file nodes (data icons); (2) data-dependent execution sequences by dynamic scheduling of path as well as loop executions; (3) host-transparency as to the location of applications and data (both can reside on any host with a unique IP address). We demonstrate that the Internet-based workflow paradigm is suitable for creation of dynamically reconfigurable desktop environments. In related research, we show that the proposed desktop is particularly suitable for making such an environment collaborative and recordable.

This paper addresses issues that arise when a peer group, distributed in time and space, uses the Internet to configure and execute distributed desktop-based applications and tasks. The paper provides solutions and Tcl/Tk implementations to support (1) peer-to-peer communication/control of distributed software and computing resources over the Internet; (2) recording and playback of interactive execution of Tcl/Tk applications and collaborative sessions. Internet-based experiments, ranging from collaborative archival applications to interactive tutorials, demonstrate the scope of distributed-team collaborative projects, and the utility of single-user and tutor-student recording and playback sessions. 1 Introduction The Internet and the on-going evolution of the world-wide web is expected to evolve into a network without technologic, geographic or time barriers -- a network over which partners, customers and employees can collaborate at any time, from anywhere, with anyone. Issues of co...

user interface for UNIX systems for more than 15 years. One result is a large installed base of X applications written in C and C++. In almost all cases, these programs rely on the Xlib library to manage their interactions with the X server. The reference implementation of Xlib is as old as X itself, and has been freely available in source form since its inception: it currently is a part of the XFree86 [xfr] distribution. Unfortunately, Xlib suffers from a number of implementation issues that have made it unsuitable for some classes of application. Most notably, Xlib is a large body of code. This is of most significance on small platforms such as hand-held computers, where permanent and temporary storage are both limited, but can also have performance disadvantages on any modern architecture due to factors such as cache size. In addition, because of Xlib’s monolithic nature, it is difficult to maintain. The authors ’ prior work on the X protocol C Binding (XCB) is intended to provide a high-quality but incompatible replacement for Xlib. While XCB is believed to be suitable for most new application and toolkit construction, it is desirable to support the large installed base of legacy code and experience by augmenting XCB with an Xlib-compatible API. This desire has led to the construction of a new library, the Xlib Compatibility Layer (XCL), that is binarycompatible with frequently-used portions of Xlib while being significantly smaller and easier to maintain. Benefits are demonstrated for both existing and new applications written for Xlib. In particular, the significant share of existing knowledge and written material about Xlib remains applicable to XCL. Also, XCL can significantly ease the migration path from Xlib to XCB.

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this documentation but makes no expressed or implied warranty of any kind and assumes no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising from the use of information or programs contained herein. Copyright c fl1994, 1995, 1996. Mark J. Kilgard. All rights reserved. All rights reserved. No part of this documentation may be reproduced, in any form or by any means, without permission in writing from the author. CONTENTS i