SK8

Overview of SK8

SK8 (pronounced "skate") was a pioneering multimedia authoring environment developed in Apple's Advanced Technology Laboratory from 1988 until 1997. The original motivating idea for SK8 was to realize a development environment that would be easy to learn and that would help people to create applications by simply drawing (visual programming).

SK8 was designed for rapid development of customizable and extensible media authoring tools and titles. SK8 was a proprietary, internal development tool used by Apple designers and engineers--it was not an Apple consumer product. SK8 has been used as a tool to prototype new ideas and products, as well as a testbed for advanced research into authoring tools and their use. The goal of SK8 has been to enable productivity gains for software developers by reducing implementation time, facilitating rapid prototyping, making development fun, and supporting cross platform development and providing output to multiple runtime environments including Java. SK8 was successfully used to create rich media tools and titles simply and quickly.

The SK8 Environment

SK8 features:
* A prototype-based, fully dynamic object system
* An English-like scripting language supporting complex declarative operations on collections
* A general and extensive graphics and event system based on containment and sophisticated rendering
* A rich object framework with support for multimedia and for tool building, fully integrated with the operating system environment.
* A feature-rich, direct manipulation development environment

The scripting language, graphics system, application framework, user interface, and various editors are explained in the [http://rubenkleiman.com/data/sk8/SK8_UserGuide.zip User Guide] .

SK8's scripting language was the first prototype implementation of AppleScript; later on it was renamed SK8Script. One of the major uses of the system was by Apple's QA group to create an automated black-box testing system. The system was used to develop prototypes for Newton, Quicktime interfaces, interprocess communication, and was used to prototype many titles, including Stagecraft, a learning tool for children. SK8's scripting technology was transferred to Kaleida (a joint Apple/IBM venture), and many projects. Outside Apple, SK8 has been seeded to over one hundred sites for evaluation and prototyping.

SK8 developers have created projects in a matter of hours. SK8 can be used to create tools designed to address specific needs. For example, media producers could create projects with time-based, event-driven and interactive book/movie sections thus adding depth and richness not available in today's authoring tools.

The Story of SK8

The SK8 project was created by Ruben Kleiman when he joined Apple in 1987. He came to Apple wishing to develop a highly flexible, object-oriented user interface and multimedia development environment which could be used to create not only applications, but also high-level development environments suitable for any specific domains (e.g., training, games, planning and scheduling, accounting and finance, music theory and performance). In addition, Ruben wanted to implement this on a Macintosh, which at that time supported a maximum of 8MB main memory. The name of the project probably derived from his interest in skateboarding.

Apple was the ideal place to start this work. HyperCard, with its direct manipulation interface and scripting language, was about to ship. While HyperCard was great for simple applications built by end users, it was too restrictive for professional programmers to use and its programming paradigm (i.e., stacks of cards) was fixed. One of the guiding questions for SK8 was how to extend these benefits to the wider programming community.

The first part of the work was devoted to developing a powerful, yet simple object system. The result was MacFrames, a very rich and powerful frame/object system. The main research focus was flexibility: to allow experimentation with object models in order to find an optimal object kernel for SK8. MacFrames was so flexible that by setting a myriad of preferences it was used to emulate a large variety of object systems, including IntelliCorp's KEE. This research, in concert with users developing actual applications and prototypes at Apple, yielded the simple and elegant model that is in SK8 today.

With this version of the object system in place, we started to work on the graphics and UI side of the system. The early SK8 graphics system used a metaphor slightly extending HyperCard (e.g., cards but with multiple layers instead of single fixed backgrounds). Around this time, the original version of SK8Script, a prototype for the first specification of the AppleScript language, was extended to a fully object-oriented scripting language based on the SK8 object model. A number of researchers in the Advanced Technology Group began to use SK8 for their projects, providing timely and intimate suggestions to improve the system. Certain universities and corporation fans began to participate: they either used SK8 as a research tool or examined it to provide detailed feedback to us.

In 1992 and 1993, to incorporate the necessary design changes while maintaining the system's elegance, we re-implemented SK8 from the ground up, resulting in the current SK8 architecture. The object system was reimplemented by manipulating the kernel of the newly acquired Macintosh Common Lisp. The graphical library and event systems now used a containment approach and conventions based on generally useful defaults. The SK8Script debugger was completed and the compiler and runtime performance improved.An object store was added to the system. The SK8 Project Builder was created to provide a very rich set of direct manipulation tools, including tools for building browsers by visual means (e.g., wiring components, expression constraints by sliders and knobs).

SK8 Personnel

Chronologically, the core SK8 team consisted of:

* Ruben Kleiman: Initial creator of SK8. Implemented versions of the object system and store, language, and graphics system. Continued developing and directed the SK8 effort until 1994.
* David Vronay: SK8 graphics and user interface.
* William Luciw: Distributed object system.
* Adam Chipkin: SK8Script.
* Hernan Epelman: Graphics and event system, applications framework, CASE tools, object store and various documentation efforts.
* Brian Roddy: User Interface, SK8Script, collections, CASE tools, SK8-Java generation and Java SK8 runtime library. Managed the project after 1994.
* Sidney Markowitz: Object system and store, condition system, build process.
* David Yost: QuickTime, OS integration.

A development team was assigned to investigate the possible productization of SK8; this team consisted of Philip McBride, Chris Flick, and Ken Dickey.

Jim Spohrer, Stephanie Houde, Alan Peterson, Matthew MacLaurin, David C. Smith, Allen Cypher, Mikel Evins, Don Tillman, Steve Seitz, and Royston Sellman provided design ideas and/or code.

Larry Tesler, Jim Spohrer, Mark Miller, Steve Weyer, and David Nagel sponsored and shepherded the project through both tumultuous and tranquil times at Apple.

References

* [http://rubenkleiman.com/data/sk8/SK8_UserGuide.zip "SK8 User Guide"] ; .zip archive of document and Apple, Inc's license agreement (1.6 MB)
* [ftp://ftp.apple.com/research/sk8 SK8 Source Code] , Apple, Inc's FTP server
* [http://www.freepatentsonline.com/5737554.html "System and method of using object sensitivity for selecting computer-generated objects"] , United States Patent 5737554
* [http://www.freepatentsonline.com/5450540.html "Graphical interface for interacting constrained actors"] , United States Patent 5450540
* [http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp=&arnumber=400042&isnumber=9020 "How to make complex software customizable"] , Systems, Man, and Cybernetics, 1994. "Humans, Information and Technology", 1994 IEEE International Conference, October 1994
* [http://www-jime.open.ac.uk/98/10/spohrer-98-10-paper.html "Educational Authoring Tools and the Educational Object Economy"] , Journal of Interactive Media in Education, 98(10), October 1998
* [http://acm.org/sigchi/bulletin/1998.2/spohrer.html#HDR7 "ATG Education Research - The Authoring Tools Thread"] , "SIGCHI Bulletin", 30(2), April 1998

External links