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language (RDL). The CDL specifies a QoS contract and it contains: nested regions
for a possible state of QoS; transitions for trigger behavior when region changes;
system condition objects for measuring QoS information; and callbacks for notification.
SDL defines the internal structure of an object and how it consumes resources,
and RDL is supposed to abstract the physical resources used by the object.
QML is a non-XML-based specification for defining multi-category QoS specifi-
cations for components in distributed object systems. Through the object-oriented
approach, it provides specification refinement and simple contract types such as
reliability and performance. Complex QoS specification can also be expressed, for
example, using percentiles, variance, and frequency aspects. Profile refinement and
conformance are defined for profile management. QML supports the specification
reusability through contract and profile refinement. The well-defined semantics and
reusability makes QDL and QML desirable QoS specifications; however, they are
not based on XML.
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