Assessing the specification of modelling language semantics: a study on UML PSSM

Abstract

Modelling languages play a central role in developing complex, critical systems. A precise, comprehensible, and high-quality modelling language specification is essential to all stakeholders using, implementing, or extending the language. Many good practices can be found that improve the understandability or consistency of the languages’ semantics. However, designing a modelling language intended for a large audience is still challenging. In this paper, we investigate the challenges and typical issues with assessing the specifications of behavioural modelling language semantics. Our key insight is that the various stakeholder’s understandings of the language’s semantics are often misaligned, and the semantics defined in various artefacts (simulators, test suites) are inconsistent. Therefore assessment of semantics should focus on identifying and resolving these inconsistencies. To illustrate these challenges and techniques, we assessed parts of a state-of-the-art specification for a general-purpose modelling language, the Precise Semantics of UML State Machines (PSSM). We reviewed the text of the specification, analysed and executed PSSM’s conformance test suite, and categorised our experiences according to questions generally relevant to modelling languages. Finally, we made recommendations for improving the development of future modelling languages by representing the semantic domain and traces more explicitly, applying diverse test design techniques to obtain conformance test suites, and using various tools to support early-phase language design.

Pragmatic verification and validation of industrial executable SysML models

“…41,42 (2) Some industrial design, simulation, and verification tool developers strive for maximum standard compliance, but this is hard to achieve due to the imprecise semantics that makes it difficult to implement the corner cases correctly. [43][44][45] (3) Furthermore, the integration of these tools is difficult in an industrial environment because the execution traces provided by them might not be consistent with each other. For example, a formal verification tool might find a trace that cannot be produced by the simulator, or the model user might come up with an execution trace that is not possible due to some limitations of the language.…”

“…For example, a formal verification tool might find a trace that cannot be produced by the simulator, or the model user might come up with an execution trace that is not possible due to some limitations of the language. 45…”

“…Although the precise definition of the semantics of UML/SysML models has vastly improved with the introduction of the fUML and PSSM specifications, there are still ambiguous interpretations in the execution semantics of activity and state machine diagrams. 45,51 The questions related to semantics are further complicated by two aspects in practice. First, tool vendors developing a modeling tool for a longer time may implement some parts based on previous specifications, or they need to fill the gaps in the specification.…”

“…This might result in inconsistent, non‐reusable models if modeling guidelines and validations are not used 41,42 . (2) Some industrial design, simulation, and verification tool developers strive for maximum standard compliance, but this is hard to achieve due to the imprecise semantics that makes it difficult to implement the corner cases correctly 43–45 . (3) Furthermore, the integration of these tools is difficult in an industrial environment because the execution traces provided by them might not be consistent with each other.…”

“…(3) Furthermore, the integration of these tools is difficult in an industrial environment because the execution traces provided by them might not be consistent with each other. For example, a formal verification tool might find a trace that cannot be produced by the simulator, or the model user might come up with an execution trace that is not possible due to some limitations of the language 45 …”