Distrbution and Abstract Types in Emerald

Reviewer: Donald Quentin Marcus Fay

In addition to describing some aspects of the Emerald language, this paper provides a good review of distributed object-oriented system design considerations. The paper is well written. It explains the problems of distribution of objects, both in general and with suitable simple examples. The motivations for the decisions made in the design of Emerald are well explained. Within the section in the paper considering support for distribution in Emerald, the following topics are discussed: object mobility, parameter passing, “call-by-name,” addressing and storage structure, object references, object descriptors, movement of objects, keeping track of mobile objects, and a reliable protocol for broadcast. This paper covers the topic well at the research and survey level and provides useful information on the problems of distributed object-oriented systems. It has a good range of references to other work in the area. The paper was written some time ago, and recent progress has shown that the mobility and distribution in the Emerald prototype perform well on distributed microVAX and SUN workstations. Some of this progress was reported at the Symposium on Operating Systems Principles in Austin, Texas in November 1987.