%% $Id: abstract.tex,v 1.11 2004/11/04 03:06:54 gokhale Exp $

\begin{abstract}

Some of the most challenging problems facing the information
technology profession are those associated with producing software for
distributed, performance-sensitive software (DPSS) systems in
which distributed resources, such as processors, sensors and networks
coordinate to control physical, chemical, or biological processes or
devices. Supporting multiple simultaneous quality of service (QoS) and
functional requirements of DPSS systems is particularly vexing for DPSS
system developers and integrators, who must address these QoS
and functional requirements without overcomplicating their solutions,
degrading software quality, and exceeding project time and effort
constraints.  A key enabler in recent successes with small- to
medium-scale DPSS systems (such as avionics systems) has been 
middleware.  However, as DPSS systems scale to form large ``composable
systems of systems'', the design space comprising available choices of
software patterns embodied in reusable middleware frameworks and
services grows substantially. This limits the ability of the DPSS
developers to make the right design choices, which adversely impacts
validation and verification of performance and correctness of end
systems, and hence project costs.  

This paper provides three contributions to the performance
evaluation of middleware-based composable DPSS systems. First, we
outline the challenges faced by DPSS developers in making the right
middleware design choices. Second, we elicit the need to conduct
performance analysis of reusable building blocks and subsequently the
application as a whole prior to the actual composition of the
application. Third, we describe a model of 
the Reactor pattern,  which provides the very important synchronous 
demultiplexing and dispatching capabilities in DPSS systems. The
model is based on the stochastic reward net modeling paradigm. 
We illustrate how the model could be used to obtain estimates of key
performance metrics and sensitivity analysis of the Reactor pattern.

\end{abstract}
