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148 Modelling of Concurrent Reactive Behaviour 6.1 Introduction The model of a complex reactive system consists of many collaborating objects that send and receive messages. In Chapter 4 we described the concepts for the static modelling of a problem domain. We defined concepts such as data objects, process objects, clusters, attributes, methods, identity, and various sorts of composites. First they enable the traditional modelling of a problem domain as related data classes and process classes. Second they enable modelling of a system as a structure of channels, processes and clusters. The modelling of structure is supported by additional concepts such as modules, views, various sorts of boundaries and transformations (defined in Chapter 5). This all covers the specification of objects and their interaction structure. The most difficult part of system analysis is the modelling of dynamic behaviour. The temporal order of events in the system and in the system environment determines this behaviour. In this chapter we present concepts for the modelling of dynamic behaviour. Various forms of concurrency, communication, distribution are described. To handle complexity we introduce scenarios. Besides the informal and incomplete description of behaviour in scenarios we present the formal statements to describe the behaviour of data objects, process objects, clusters and systems. This chapter ends with a brief overview of our current research to the extension of SHE with real-time concepts. 6.2 Concurrency and Synchronisation 6.2.1 Introduction A specification method requires a natural and adequate concurrency concept. Concurrency must be defined such that two goals can be reached. Firstly, the concept of concurrency must have the intuitive meaning of parallelism so that a model of a system can be interpreted in a natural way. The meaning of a specification model must be such that it can be understood easily by various (non) experts. Second the concept of concurrency must be implementable in hardware as well as in software. Concurrency in general, and especially in object-oriented languages, is still a subject for research. In this section we introduce concepts for the modelling of concurrent systems such as asynchronous concurrency, synchronous concurrency, interleaving semantics, synchronisation for communication and non-determinism. (These subjects are strongly related to the modelling of dynamic behaviour, see also Section 6.6.2.) 6.2.2 Concurrency 6.2.2.1 Concurrent Process Objects and Sequential Data Objects We introduced objects and clusters as concepts that enable modularisation of a problem domain. We repeat the definitions of process data objects and clusters briefly. These concepts were defined in Chapter 4 using the notion of concurrency without defining what concurrency really means.
6.2 Concurrency and Synchronisation 149 We defined process objects as entities that can perform their behaviour concurrently to each other: Process objects can model concurrent independent system parts (connected in a static channel structure). The internal behaviour of process objects is sequential. Collaborating data objects perform sequential behaviour. They model passive entities that must be activated by a message. Only one data object from a collection of collaborating data objects is actively processing. Together with a message the thread of activity goes from sender to receiver. In general, collaborating data objects model a part of the internal sequential behaviour of a process object. Two data objects that belong to two different process objects can operate concurrently. These objects are completely independent and cannot directly communicate with each other. A cluster is an abstraction boundary around a group of collaborating process objects and clusters. In contrast to process objects, clusters can have internally concurrent behaviour. Internally concurrent behaviour is specified in a cluster class by a parallel composition of processes and clusters (subsystems). The internal concurrency of a cluster is solely established by its process objects. Clusters can be used to specify whether the internal behaviour of a subsystem is sequential or concurrent. Such a cluster is defined to be a concurrency boundary. This is an enclosure that prescribes that the cluster has an internal sequential behaviour (see Paragraph 5.8.2.4). This means that collaborating processes inside the boundary form a composite that must be modelled such that it performs a sequential behaviour. This requirement determines the behaviour style of the individual processes. This style is determined by the sort of communication and synchronisation that must be used to specify the behaviour of these processes. A subsystem that must be implemented sequentially can have only one process active simultaneously. In that case the whole subsystem has only one internal thread of activity. Synchronisation between objects in such a subsystem implies that process objects pass the thread of activity together with the message, just like data objects do. 6.2.2.2 Asynchronous Concurrency By defining process objects as independent concurrent entities, we appealed to a general intuition of concurrency, which is so-called asynchronous concurrency. This form of concurrency enables processes to be independent in time. Processes are defined to be asynchronous concurrent if they perform their actions at their own speed. This approach is natural for distributed systems that are implemented by a collection of interconnected processing elements that may run at different internal speeds. The intuitive notion of concurrency takes time into account. Two operations, in two different process objects, are thought to take time to be completed. Concurrent operation means that both operations run simultaneously, at least during some period of time. The
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Specification of Reactive Hardware/
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to Leny, Inge and our parents
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Contents Acknowledgements v 1 Intro
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CONTENTS ix 4.6.5 Aggregate Semanti
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CONTENTS xi 6 Modelling of Concurre
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CONTENTS xiii 6.6.7.2 System Specif
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CONTENTS xv 11.4.2.3 Requirements C
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List of Figures 1.1 Chapter Overvie
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LIST OF FIGURES xix 6.16 Strongly D
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Chapter 1 Introduction 1.1 Objectiv
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1.1 Objectives 3 understood and sti
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1.1 Objectives 5 Informal and Forma
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1.2 Thesis Organisation 7 Chapter 1
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1.2 Thesis Organisation 9 Recommend
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Chapter 2 On Specification of React
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2.3 Specifications, Models and View
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2.4 Specification Languages, Formal
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2.4 Specification Languages, Formal
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2.5 Modelling Concepts 23 entirety.
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2.5 Modelling Concepts 25 Tradition
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2.6 Activity Frameworks for Specifi
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2.6 Activity Frameworks for Specifi
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2.7 Summary 31 offer many guideline
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Chapter 3 Concepts for Analysis, Sp
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3.3 Concepts 35 3. creation of a sy
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3.5 Combining Compatible Concepts 3
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3.6 Practical Use of Concepts 39 3.
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3.6 Practical Use of Concepts 41 Th
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3.6 Practical Use of Concepts 43 ac
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3.6 Practical Use of Concepts 45 ac
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3.6 Practical Use of Concepts 47 wa
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3.6 Practical Use of Concepts 49 Ge
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3.6 Practical Use of Concepts 51 Re
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3.7 Summary and Concluding Remarks
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Chapter 4 Abstraction of a Problem
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4.1 Introduction 57 earlier phase t
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4.2 Objects 59 An object can mean t
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4.2 Objects 61 wonder what other ob
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4.3 Classes 63 A message interface
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4.3 Classes 65 Class B Attributes M
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4.4 Data Objects and Process Object
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4.5 Clusters 79 flows. Clusters ena
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4.6 Aggregates 81 Therefore a compl
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4.6 Aggregates 83 4.6.4 Clustered A
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4.6 Aggregates 85 An old philosophi
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4.7 Identity and Object Identifiers
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4.8 Properties of Composites 89 for
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4.8 Properties of Composites 91 com
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4.8 Properties of Composites 93 Whe
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4.8 Properties of Composites 95 In
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Page 121 and 122: 4.12 Object Variety 101 Part class
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Page 127 and 128: 4.14 Attributes and Variables 107 c
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Page 131 and 132: 4.15 Operations, Services, Methods
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Page 135 and 136: 4.17 Summary 115 Accidental Propert
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Page 139 and 140: 5.2 Architecture 119 Requirements D
Page 141 and 142: 5.3 Design Philosophy 121 this. The
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Page 147 and 148: 5.6 Architecture and Implementation
Page 149 and 150: 5.7 Views 129 Management £ £ £ P
Page 151 and 152: 5.7 Views 131 Behaviour Behaviour U
Page 153 and 154: 5.8 Boundaries 133 5.8 Boundaries 5
Page 155 and 156: 5.8 Boundaries 135 x x Object A y z
Page 157 and 158: 5.8 Boundaries 137 x w w x Object A
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Page 161 and 162: 5.9 Transformations 141 The modific
Page 163 and 164: 5.10 Formalisation 143 Level 1 Leve
Page 165 and 166: 5.11 Summary 145 Behaviour Requirem
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Page 171 and 172: 6.2 Concurrency and Synchronisation
Page 177 and 178: 6.3 Communication 157 between proce
Page 179 and 180: 6.3 Communication 159 or to transfo
Page 181 and 182: 6.3 Communication 161 6.3.3.4 Messa
Page 183 and 184: 6.3 Communication 163 Synchronous m
Page 185 and 186: 6.3 Communication 165 channel-name
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Page 189 and 190: 6.3 Communication 169 statement aft
Page 191 and 192: 6.3 Communication 171 (normalCourse
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Page 195 and 196: 6.3 Communication 175 There is a gr
Page 197 and 198: 6.3 Communication 177 process A pro
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Page 201 and 202: 6.3 Communication 181 whether the s
Page 203 and 204: 6.3 Communication 183 6.3.9.4 Model
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Page 207 and 208: 6.4 Distribution 187 force to take
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Page 215 and 216: 6.5 Scenarios 195 entities. This su
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6.5 Scenarios 199 collection of tex
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6.6 Dynamic Behaviour 201 selection
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6.6 Dynamic Behaviour 203 processes
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6.6 Dynamic Behaviour 205 even for
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6.6 Dynamic Behaviour 207 with the
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6.6 Dynamic Behaviour 209 6.6.4 Sep
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6.6 Dynamic Behaviour 211 6.6.5 Mod
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6.6 Dynamic Behaviour 213 to pay at
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6.6 Dynamic Behaviour 215 A method
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6.6 Dynamic Behaviour 217 to happen
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6.6 Dynamic Behaviour 219 c a Multi
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6.6 Dynamic Behaviour 221 but not t
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6.7 Real-Time Modelling 223 claimed
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6.7 Real-Time Modelling 225 in the
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6.8 Summary 227 They can graphicall
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Chapter 7 Introduction to the Seman
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7.2 A Brief Language Characterisati
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7.3 The Role of Semantics 233 7.3 T
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7.4 Mathematical Preliminaries 235
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7.4 Mathematical Preliminaries 237
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7.5 Concluding Remarks 239 0 ¡ Bin
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Chapter 8 Data Part of POOSL Chapte
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8.3 Formal Syntax 243 runk, and cun
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8.4 Context Conditions 245 Further,
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8.5 A Computational Semantics 247 T
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8.5 A Computational Semantics 249 w
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8.5 A Computational Semantics 251 s
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8.6 Primitive deepCopy Messages 253
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8.6 Primitive deepCopy Messages 255
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8.7 Example: Complex Numbers 257 is
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8.8 Summary and Concluding Remarks
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Chapter 9 Process Part of POOSL Cha
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9.3 Formal Syntax 263 In almost any
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9.3 Formal Syntax 265 The fourth st
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9.3 Formal Syntax 267 call of the f
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9.4 Context Conditions 269 We are n
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9.5 A Computational Interleaving Se
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9.6 Example: A Simple Handshake Pro
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9.7 The Development of POOSL 291 is
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9.7 The Development of POOSL 293 da
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9.7 The Development of POOSL 295 e
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9.7 The Development of POOSL 297 Em
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9.7 The Development of POOSL 299 (o
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9.8 Summary 301 To prepare the deve
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Chapter 10 Behaviour-Preserving Tra
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10.2 Instance Structure Diagrams 30
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10.2 Instance Structure Diagrams 30
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10.3 Some Properties of Transformat
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10.4 A System of Basic Transformati
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10.5 Example: The Elevator Problem
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10.7 On the Fundamental Limitations
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10.7 On the Fundamental Limitations
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10.8 Summary 331 are transformation
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Chapter 11 SHE Framework Chapter 1
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11.2 SHE Context and Phases 335 Inf
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11.2 SHE Context and Phases 337 a p
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11.2 SHE Context and Phases 339 11.
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11.3 SHE Framework 341 the system.
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11.4 Essential Specification Modell
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11.5 Extended Specification Modelli
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Chapter 12 Case Study Chapter 1 Cha
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12.2 Initial Requirements Descripti
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12.3 The Essential Specification 37
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12.4 Towards an Extended Specificat
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12.5 Concluding Remarks 399 i1 DIST
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12.5 Concluding Remarks 401 Feeder
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Chapter 13 Conclusions and Future W
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13.2 P.H.A. van der Putten’s Cont
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13.2 P.H.A. van der Putten’s Cont
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13.4 Related Results 409 The notion
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Appendix A The POOSL Transition Sys
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A.1 The Data Part of POOSL 413 (12)
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A.2 The Process Part of POOSL 415 A
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A.2 The Process Part of POOSL 417 (
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A.2 The Process Part of POOSL 419 (
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A.2 The Process Part of POOSL 421 i
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Appendix B Proofs of Propositions a
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Proofs of Propositions and Transfor
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Appendix C Glossary of Symbols This
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Glossary of Symbols 437 267 Cp ¥¡
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References [AB90] P. America and F.
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REFERENCES 441 [C [C [C 86] B. Cohe
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REFERENCES 443 [Her90] A.J.H. Herbe
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REFERENCES 445 [MV93] S. Mauw and G
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REFERENCES 447 [vE89] P. van Eijk.
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Index abort, 297 abstract action so
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INDEX 451 strong, 190, 293 subsyste
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INDEX 453 delay, 178 do-statement,
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Summary This combined thesis descri
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Samenvatting Dit gecombineerde proe
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Curricula Vitae Piet van der Putten
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