Slicing UML's Three-layer Architecture: A Semantic Foundation for Behavioural Specification by Michelle Love Crane A thesis submitted to the School of Computing in conformity with the requirements for the degree of Doctor of Philosophy Queen's University Kingston, Ontario, Canada January 2009 Copyright © Michelle Love Crane, 2009 Abstract One of the main notational contexts in which model-driven software development has been studied is the Uni¯ed Modeling Language (UML), the de facto standard in software modelling. The current trend in software development is not just towards the use of models, but the use of executable models. In 2006, the Object Management Group issued a Request for Proposal (RFP), soliciting the de¯nition of an Executable UML Foundation, with a fully speci¯ed executable semantics. The purpose of such a version of UML is to make the advantages of executable models available to UML users by enabling \a chain of tools that support the construction, veri¯cation, translation, and execution" of models. An oft-voiced criticism of UML is its lack of a formal, unambiguous description of its semantics. In an e®ort to improve the support for model-driven development, especially with respect to executable modelling, the UML 2 speci¯cation introduced a novel three-layer semantics architecture. This architecture provides a strati¯cation of the description of UML models that clearly separates `low-level' behavioural spec- i¯cation mechanisms, such as actions, from `high-level' behavioural formalisms, such as activities, state machines and interactions. Although UML describes the e®ect of actions, it does not provide either the concrete syntax or the formal semantics of an action language. i Our research focuses on a top-to-bottom slice of the three-layer architecture. We formally de¯ne the execution semantics of two-thirds of UML actions, including the most complicated actions|invocation actions. Our formal de¯nition is expressed in terms of state changes to a global state machine representing an executing UML model. Our work provides an alternate formalization to that of the current submission to the RFP and could be used to enhance that submission. To validate our formal semantics and to determine the usefulness of the three-layer architecture, we have created an interpreter for UML actions and activities. This in- terpreter was designed in accordance with the complex token passing semantics of UML and provides analysis capabilities that have been successfully used to identify problems even in published activity diagrams. In e®ect, we have created a tool that supports the construction, veri¯cation and execution of a subset of UML models, namely activities. Our handling of this slice of the three-layer architecture is a pre- liminary step to realizing the grander vision of general executable (and analyzable) models. ii Co-Authorship Some parts of Chapters 3, 4 and 5 were written in collaboration with my supervisor Dr. Juergen Dingel and were presented [19] at the 11th International Conference on Model Driven Engineering Languages and Systems (MoDELS 2008). The majority of Chapter 7 was written in collaboration with my supervisor and was presented [20] at the 2008 conference of the Centre for Advanced Studies on Collaborative research (CASCON 2008). The grammar in Appendix C appears as part of a technical re- port [31] at the National Institute of Standards and Technology (NIST). The grammar was created in isolation, although the technical report itself was written in collabora- tion with two other authors, David Flater, of NIST, and Philippe Martin, of Gri±th University. iii Acknowledgments This research is supported by the Centre of Excellence for Research in Adaptive Systems (CERAS) and IBM. An ongoing project, it has also been supported over the years by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Ontario Graduate Scholarship (OGS) program. Formally, I would like to thank Juergen Dingel for being an inspiring supervisor and mentor. I also appreciate his commitment to excellence and amazing turnaround time, both of which are helping me achieve my goals. I would also like to thank Bran Selic of Malina Software Corporation and Conrad Bock of the National Institute of Standards and Technology for their invaluable assistance with the intricacies of UML. Informally, I would like to thank the professors, students and sta® of the School of Computing for making it such an interesting experience. Most especially, I'd like to thank Bob Tennent, tongue-in-cheek, for scaring me so badly on the very ¯rst day of my prep year. Come up with a perfect binary search in 30 minutes, indeed. I'd like to thank my family and Queen's friends: Mom, the folks, Amber, Dean, Jeremy, Richard, and anyone else I've ever had a long rambling conversation with. To Val, once again, I thank you for your continued support. We're almost there! And ¯nally...most of all, this one's for me. iv Statement of Originality I hereby certify that all of the work described within this thesis is the original work of the author. The research was conducted under the supervision of Dr. Juergen Dingel. Any published (or unpublished) ideas and/or techniques of others are fully acknowledged in accordance with the standard referencing practices. Michelle L. Crane January 2009 v Table of Contents Abstract i Co-Authorship iii Acknowledgments iv Statement of Originality v Table of Contents vi List of Tables x List of Figures xi Chapter 1 Introduction . 1 1.1 Problem . 2 1.2 Thesis and Scope of Research . 4 1.3 Organization of Thesis . 5 Chapter 2 Background . 7 2.1 UML Semantics Architecture . 7 2.2 Semantic Domain . 9 vi 2.3 UML Actions . 9 2.4 UML Activities . 22 Chapter 3 System Model . 32 3.1 Document Conventions . 32 3.2 Structure . 35 3.3 State . 47 Chapter 4 Structure of Activities . 62 4.1 Control Store for Activities . 63 4.2 De¯ning Activities . 67 4.3 De¯ning Enablement . 75 Chapter 5 Actions . 80 5.1 De¯ning Actions . 80 5.2 Semantics of Actions . 82 5.3 Invocation Actions . 122 5.4 Pragmatics of Invocation Actions . 154 5.5 Summary of Changes to State . 159 Chapter 6 Execution of Activities . 164 6.1 Token O®ers . 165 6.2 Initialization . 167 6.3 Execution Algorithm . 167 6.4 Data Flow . 179 Chapter 7 Interpreter . 180 vii 7.1 ACTi . 181 7.2 Analysis . 192 Chapter 8 Evaluation . 200 8.1 User-de¯ned Action . 201 8.2 Shallow Exploration . 206 8.3 Simple Activity . 215 8.4 USE Visualization . 224 8.5 Accept Call vs. Accept Event . 230 8.6 Inheritance and Dynamic Binding . 232 Chapter 9 Related Work . 237 9.1 Surface Language and Executable UML . 238 9.2 Executable UML Foundation . 241 9.3 Summary . 243 Chapter 10 Conclusion . 245 10.1 Contributions . 246 10.2 Future Work . 256 Bibliography . 263 Appendix A Metamodels of Actions . 273 Appendix B Examples . 285 B.1 Example 1: Create and Read Object . 285 B.2 Example 2: Specify Value and Test Identity . 287 viii B.3 Example 3: Read Extent and Destroy Object . 289 B.4 Example 4: Structural Feature Actions . 291 B.5 Example 5: Variable Actions . 294 B.6 Example 6: Start Classi¯er Behaviour and Read Self . 297 B.7 Example 7: Call Behaviour . 299 B.8 Example 8: Call Operation . 302 B.9 Example 9: Send Signal and Accept Event . 305 Appendix C ADLF . 309 C.1 Motivation . 310 C.2 EBNF Grammar for ADLF . 312 Appendix D cd and obj Files . 316 D.1 Conventions . 316 D.2 EBNF Grammar for cd Files . 317 D.3 EBNF Grammar for obj Files . 319 Index . 321 ix List of Tables 2.1 UML actions by package and function . 12 5.1 Invocation actions along two dimensions . 123 5.2 Summary of invocation actions . 155 5.3 Code statements to invoke behaviour . 156 5.4 Invocation actions (including StartClassi¯erBehaviorAction) . 157 5.5 Summary of state changes . 160 7.1 ACTi modes of execution . 187 x List of Figures 2.1 The UML three-layer semantics architecture . 8 2.2 Hierarchy of communication actions . 13 2.3 Hierarchy of object actions . 14 2.4 Hierarchy of structural feature actions . 16 2.5 Hierarchy of link actions . 17 2.6 Hierarchy of variable actions . 18 2.7 Hierarchy of other actions . 19 2.8 UML metamodel of ReadIsClassi¯edObjectAction . 21 2.9 Action nodes . 23 2.10 Initial node . 23 2.11 Activity ¯nal node . 24 2.12 Flow ¯nal node . 24 2.13 Fork node . 24 2.14 Join node . 24 2.15 Decision node . 25 2.16 Merge node . 25 2.17 Object nodes . 25 2.18 Standalone pin notation . ..