USENIX Technical Program - Abstract - COOTS 99
Quality of Service--Aware Distributed Object Systems
Svend Frølund, Hewlett-Packard Laboratories; Jari Koistinen, Commerce One, Inc.
Computing systems deliver their functionality at a certain level of performance,
reliability, and security. We refer to such non-functional aspects as
quality-of-service (QoS) aspects. Delivering a satisfactory level of QoS is very
challenging for systems that operate in open, resource varying environments such
as the Internet or corporate intranets. A system that operates in an open
environment may rely on services that are deployed under the control of a
different organization, and it cannot per se make assumptions about the QoS
delivered by such services. Furthermore, since resources vary, a system cannot
be built to operate with a fixed level of available resources. To deliver
satisfactory QoS in the context of external services and varying resources, a
system must be QoS aware so that it can communicate its QoS expectations to
those external services, monitor actual QoS based on currently available
resources, and adapt to changes in available resources.
A QoS-aware system knows which level of QoS it needs from other services and
which level of QoS it can provide. To build QoS-aware systems, we need a way to
express QoS requirements and properties, and we need a way to communicate such
expressions. In a realistic system, such expressions can become rather complex.
For example, they typically contain constraints over user-defined domains where
constraint satisfaction is determined relative to a user-defined ordering on the
domain elements. To cope with this complexity we are developing a specification
language and accompanying runtime representation for QoS expressions. This paper
introduces our language but focuses on the runtime representation of QoS expressions.
We show how to dynamically create new expressions at runtime and how to
use comparison of expressions as a foundation for building higher-level QoS
components such as QoS-based traders.
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