The gang-of-four's Observer pattern describes how we can define a one-to-many dependency between objects so that, when the object changes, all its dependants are notified of this change. The purpose of this dependency is to achieve consistency of state between loosely coupled objects as exemplified by the Model-View-Controller framework used in Smalltalk-80.
This loose coupling of objects is one of the defining characteristics of systems built with CORBA or COM/DCOM where dependant objects may exist in different process on the same machine, or on a different machine separated by a Lan or Wan. In the context of a distributed environment, many of the issues dealt with by Observer become far more complicated, for example:
New issues are also introduced such as the synchronisation of subjects and observers operating asynchronously.
The purpose of this working group is to explore the issues of consistent state and synchronisation in distributed environments. The type of questions we'll deal with include:
In answering these and other questions we will look to formulate a skeleton pattern language or design-decision tree (DDT). This language or DDT will attempt to capture the shared knowledge and experiences of the working group in solving these problems. This language or DDT will form the basis of a poster for the conference and will be distributed to all members of the group following the conference.
In order to join this working group you need to submit a position paper to one of the sessions leaders. Possible form for this paper include: an experience report, a set of requirements for distributed object synchronisation in a system, or a list of questions and partial answers. A typical paper would be between 3-10 pages long and would contain some indication of the authors experience in this area (which might be none, some or lots!) and the specific issues they want to deal with in the group. Papers should be emailed to one or both of the session leaders by 20th March in either plain text, html or pdf format, and will be distributed to all members of the group 2-3 weeks before the conference takes place.
Paul Dyson has, with Bruce Anderson, run two successful workshops on 'Design Variation and Architecture' at previous Object Technology conferences. Paul has also presented papers and posters on patterns and architecture at a number of international conferences including OOPSLA and OOP. Paul has recently joined Cumulus Systems Ltd., a software house that develops systems for the financial sector. Cumulus is currently developing an integrated front and back office product in a totally OT-based environment based around a CORBA ORB, ODBMS and Smalltalk.
Paul Dyson, Cumulus Systems Ltd., 1 High Street, Rickmansworth, Herts., WD3 1ET, UK. Tel: +44.1923.720477. paul@cumulus.co.uk
Andy Moorley has jointly run successful workshops on Subjectivity and 'ORBs and ODBMs' at OT '96 and '97. Andy is now with JP Morgan (London) where he is working on an OO derivatives risk management system based on Smalltalk, ODBMS and ORB technology. He has both architectural and development roles in this project.
Andy Moorley, JP Morgan, PO Box 161, 60 Victoria Embankment, London. EC4Y 0JP, UK. Tel: +44.171.353.8658. moorley_andy@jpmorgan.com