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	Ada-Europe'96 Conference Workshop on Design Patterns for Active Objects

Purpose

The purpose of this workshop is to provide a forum for workers interested in formulating and discussing design patterns using active object techniques in Ada 95.

Active objects are objects that have or use a thread of control as a part of their state.

Active objects are a crucial design paradigm for many types of systems, particularly those involving concurrency, parallelism or distribution (CPD), and those which are performance or resource-constrained. Even in "sequential" systems, active objects provide a useful technique for abstracting and constructing behaviors.

Within the Ada community there has been lively development of idioms for active objects since the early days of the language - even before the term "design patterns" was in use! See for example, Hibbard et al., Ray Buhr's work, DRAGOON, Luckham's Anna and TSL.

Meanwhile, as the object-oriented programming community has confronted concurrency, there has been a line of work from Morven Gentleman through several recent workshops at OOPSLA. Another source of interest in these issues is the blossoming concerns for "threads and thread-safe implementations" by the implementors and applications developers of frameworks such as X, POSIX, CORBA, DCE.

With the advent of Ada 95, its features for full object-oriented programming, concurrency, and distribution offer designers a new repertoire of implementation features. In addition, developers must increasingly confront how to design applications that work with "imported behaviors" employing paradigms such as CORBA and DCE. The rich semantic basis of Ada 95 to discuss concurrency, synchronization, and distribution in an object-oriented style make it a most appropriate choice for describing and recording design patterns for this domain. See Burns and Wellings for an excellent overview of Ada language capabilities in this area.

Workshop Goals

Among the goals of this workshop will be to:

• Capture and articulate design knowledge and expertise from a wide variety of practitioners and researchers.
• Catalog and document this expertise using the recent "design patterns" paradigm. Patterns is a useful medium for communicating this expertise both within/without the Ada community.
• Outline a taxonomy of active object types such as: actors, agents, clients, servers, robots, notifiers, etc.
• Investigate open issues pertaining to active objects, such as synchronization inheritance, behavioral composition, and open implementation.
• Explore idioms for composition. How do we separate "policy" from functionality? What are the limitations of genericity, subclassing, mixins, and other forms of parameterization?
• Identify the limitations of the patterns paradigm. Are patterns as currently understood sufficient to express behaviors that cannot be "localised" to individual objects or components?

Requirements for Participation

Position papers (2-3 pages) will be sought relating to one or more of the following:

• Proposed active object patterns. (Participants are encouraged to submit any proposed patterns in the "Gang of Four" format. Templates may be found on the Patterns Home Page.)
• Issues relating to conception and use of active object patterns.
• Taxonomies for active object types, and bases for taxonomies
• Idioms and experience (good or bad experiences!), including: patterns seeking implementations, bases for taxonomies
• Limitations of pattern use
• Relationship to other software technologies, including: object-oriented design and other methods, tools and processes

All papers must be written in English. Authors should submit their papers electronically in Postscript format to the organizers by 1 April 1996. Submissions should include complete contact information (name, affiliation, address, phone, fax, email, and WWW home page, if applicable).

Submissions will be reviewed by the organizers. Authors will be notified of the acceptance or rejection of their papers by 1 May 1996. Accepted papers will be made available for review by all potential workshop participants prior to the date of the workshop via the World-Wide Web.

Important Dates

• Position papers are due by 1 April 1996
• Notification of acceptance is 1 May 1996
• Workshop will be held Monday, 10 June 1995

Format of Workshop

An introductory talk on the workshop goals and sample patterns will be given by the organizers.

Four submissions will be chosen from the submissions to be the subject of 20 minute presentations to motivate and stimulate discussion.

The next hour will be spent in group dialogue to develop a work plan for further actions. Work groups will be defined for meeting during the first portion of the afternoon.

Two hours of the afternoon will be spent in workgroups.

Workgroup reports will be given for one hour.

The remainder of the session will be devoted to discussion of open issues and the formulation of future activities.

Workshop Organizers

Mark Gerhardt
Software Engineering Lab
Loral Space and Range Systems
1260 Crossman Avenue
Sunnyvale, CA 94089
Gerhardt_Mark@srs.loral.com

Rich Hilliard
The MITRE Corporation
M/S B155
Bedford, MA 01730
rh@mitre.org

References

Agha, et al. Proceedings of the ACM SIGPLAN Workshop on object-based concurrent computing. In SIGPLAN Notices 24(4), 1989. Also see http://www.cs.wustl.edu/~schmidt/OOPSLA-95/index.html