#Number
TR-PDS-1996-007

#Title 
The Sage Project: Software Engineering for Distributed Applications


#Author
Aleta Ricciardi and Chun Chan

#Abstract This paper describes Sage, a research project in software
engineering for (fault-tolerant) distributed applications that assists
programmers write correct, efficient code.  Specifically, Sage uses the
modal logic of knowledge and applies theoretical results detailing how
processes learn facts about each other's state to derive the minimal
communication graph for a given distributed coordination problem.  An
environment that applies intricate theoretical results, but hides the
theory from users is particularly important as few distributed applications
programmers hold advanced degrees in computer science.

The specification interface is controlled, yet expressive enough to capture
canonical distributed coordination problems and weaker variants appropriate
for wide-area and object-oriented systems.  The resulting graphical display
shows programmers which messages must be received.  Sage allows users to
experiment on the derived protocol by crashing processes, reordering
events, losing messages, and partitioning the network.  Under these
conditions, Sage regenerates the communication graph, or indicates a
solution is now impossible.  This has two benefits: it animates the effects
of unpredictable system events on distributed applications, and it greatly
simplifies testing distributed algorithms.  Sage completely separates the
issues in testing a protocol's behavior in the face of failures, from the
effects background system conditions (e.g. processor or network loads) can
have on the testing procedure itself.

As development continues, other components will highlight required group
and communication primitives, generate skeleton code, and verify user-drawn
protocols.  Thus, Sage will be an integrated development, testing and
verification environment for distributed applications.

Keywords: software fault tolerance; highly-available software systems;
distributed systems; specification and design of reliable software-based
systems.

#Bib