Abstract

The paper compares two UML Profiles adopted by OMG for annotating non-functional requirements of software systems: the UML Profile for Schedulability, Performance and Time (SPT) formally adopted in 2003 and the recently emerging UML Profile for Modeling Quality of Service and Fault Tolerance Characteristics and Mechanisms (QoS). The SPT Profile was the first attempt to extend UML with basic timing and concurrency concepts, and to express requirements and properties needed for conducting schedulability and performance analysis. While the SPT Profile is focused on these two types of analysis, the more recent QoS Profile has a broader scope, aiming to allow the user to define a wider variety of QoS requirements and properties. In order to compare the two profiles, we will focus on performability and timing aspects of software systems, by exemplifying the concepts through an example of embedded automation system. The comparative analysis shows that new concepts are needed in both profiles to express time intervals between two arbitrary events. Also, the two profiles will need to reach a common agreement on the specification of complex timing values, especially of those with stochastic characteristics. Another open problem is the parameterization of models, as in many cases fixed values for model parameters are not enough. The SPT Profile goes a step further by supporting symbolic variables and expressions, but the QoS Profile does not have such a capability yet. In general, both Profiles struggle with the balance between flexibility (i.e., allow the user to introduce its own definitions) and simplicity/convenience of expression. The challenge when defining a UML profile is to find convenient yet powerful mechanisms of expression for complex concepts, yet to remain within the limits of the UML standard extension mechanisms, which is necessary to insure that the annotated models could be understood by standard UML tools.

Citations