The authors begin with Saguaro’s Universal Type System (UTS). The UTS is used to describe both stored data (e.g., files) and also interface specifications for commands and procedures. The application of UTS is then illustrated by describing how various command interpreters can be constructed. Following this, the paper describes several mechanisms for distributed systems support provided by Saguaro.

Three specific mechanisms are described: channels, reproduction sets, and metafiles. A channel is a variant of the pipe that allows multiple readers; each gets a copy of the data. A reproduction set is a collection of files that the system attempts to keep consistent on a best effort basis. A metafile is a generalization of the symbolic link that allows one to specify a set of filenames instead of a single replacement name.

The paper concludes by giving a summary of the Saguaro system architecture.

The discussion of the UTS and its application is clearly written. In particular, the description of how command interpreters can be implemented and the use of syntactic sugaring to mask the rigid typing is excellent.

The rest of the paper is also well done. Not all the mechanisms described are new, but they are well presented. I felt, however, that the paper could have been strengthened had there been more justification for the authors’ choice of mechanisms to include. Overall, I found the ideas presented in the paper to be interesting and useful.