Problems in Implementing Flexible Group Communication with Email

Group communication with email is performed by multicast making use of mailing lists. However, it is not quite possible to exclude any member out of the list temporarily. We try and apply some of the set operations to the destination address of a message to solve the problem. The idea is viewing email addresses as a language. Our prototype system works within a domain, however, in reality mailing lists are managed in a distributed fashion over the Internet. We need some control over access to those mail lists. This paper presents our model of grouping and reports the implementation of a prototype system as well as some access control issues to be dealt with when we extend our system over the global Internet. 1 Overview and Motivation Suppose that we have an email mailing list of friends, and we need to discuss about the birthday present for one of the members on the list one day. We would wish to exclude that friend out of the list only with the messages related to that discussion. The current email system is not so adaptive that one can exclude a member out of a mailing list temporarily on such a message basis. From such perspective, we try and apply some of the set operations to the destination address eld of a message to solve the problem. The idea is viewing email addressing as a language. Our prototype system works within a domain, however, in reality mailing lists are managed in a distributed way over the Internet. We need some control over access to those lists. Most work on intelligent email and mailing lists[2][1][4] has been concerned with management of email as an information base, and has not looked at email addressing for group communication. Ueda et al.[6] developed a system in which the destination address can be speci ed by attributes of the receivers using some information retrieval language. They took an approach from the database viewpoint and constructed a database system completely di erent from the current email system and it worked only in one domain. They, therefore, did not come across the issues on information exchanging problems which we present in Section 6. This paper is organized as follows. The next section discusses group communication with email by presenting the model for naming groups. Section 3 presents our idea to incorporate set operations to email addressing. Section 4 describes the design issues of the system model, and section 5 reports our trial to implement a prototype system. Section 6 discusses limitation of our prototype system and some problems incurred when one runs such systems over the global Internet. 2 A Model of Grouping In this section we present a mathematical model for grouping and discuss why we propose set operations to mailing lists. Figure.1 shows a simple conceptual view of the sets and functions of the model. We de ned four sets in our model, viz. E, P(E), G and N . E is a set of entities in the minimum unit for a group member. In case of email mailing lists, it