Message Sequence Charts are a widely used technique for the visualization of the communication between system components. We present a formal semantics of Basic Message Sequence Charts, exploiting techniques from process algebra. This semantics is based on the semantics of the full language as being proposed for standardization in the International Telecommunication Union.

this paper is to give an informal tutorial on this process algebra semantics. Currently, the static requirements are formalized [10]. It is investigated whether other parts of Z.120 also need formalization. The second goal of this paper is to describe the state of affairs with respect to the formalization of MSC and to indicate which parts possibly need further formalization. The main motivation for formalization is that users of the language need to understand each other precisely. An MSC should have only one interpretation. Ambiguities, inconsistencies and obscurities hamper proper use of the language. This implies not only that the semantics of MSC must have a formal base, but that also the appearance and use of MSCs should be formalized as much as possible. If two computer tools for MSC do not agree on the collection of admitted MSCs, they are not able to exchange MSCs. If there are two incompatible ways to transform an MSC from graphical representation into textual representation, this will lead to problems. This paper is organized as follows. In Section 2 we discuss the state of affairs with respect to the formalization of MSC. In Section 3 we give a tutorial on the formal semantics. This paper does not contain an introduction to the MSC language. Please refer to the aforementioned literature for more information about MSC. 2 Acknowledgements

this paper we will define this operator within the framework of BPA " . This is the concurrency theory BPA (Basic Process Algebra) extended with the empty process

We discuss four issues concerning the semantics of Message Flow Graphs (MFGs). MFGs are extensively used as pictures of message-passing behavior. One type of MFG, Message Sequence Chart (MSC) is ITU Standard Z.120. We require that a system described by an MFG has global states with respect to its message-passing behavior, with transitions between these states effected by atomic message-passing actions. Under this assumption, we argue (a) that the collection of global message states defined by an MFG is finite (whether for synchronous, asynchronous, or partially-asynchronous message-passing); (b) that the unrestricted use of `conditions' requires processes to keep control history variables of potentially unbounded size; (c) that allowing `crossing' messages of the same type implies certain properties of the environment that are neither explicit nor desirable, and (d) that liveness properties of MFGs are more easily expressed by temporal logic formulas over the control states than by Buc...

Introduction Recently, the ITU 1 -standardised specification language Message Sequence Chart (MSC) [IT96] has been extended with constructs for more complete and structured specifications. The new version of the language is called MSC'96. Currently, research is performed on the extension of the old formal semantics towards a semantics for MSC'96. Ideally, the development of a language and its semantics should go hand in hand. There is little use in defining a fancy syntactic construction without a precise understanding of its meaning. As was the case for the old version of the MSC language, first the syntax and an incomplete and informal semantics were developed, while the construction of a formal semantics was deferred until after the acceptance of the language by the ITU bodies. It is obvious that the a-posteriori construction of a formal semantics will reveal many places in which the informal language description is ambiguous, under-specified, inconsistent

Message Sequence Charts is a graphical and textual language for the description and specification of the interactions between system components and their environment. The language is standardized by the ITU-TS (the Telecommunication Standardization section of the International Telecommunication Union, the former CCITT). The main area of application for Message Sequence Charts is as an overview specification of the communication behavior of real time systems, in particular telecommunication switching systems. Message Sequence Charts may be used for requirement specification, interface specification, simulation and validation, test case specification and documentation of real time systems. In this paper we present a formal semantics of Message Sequence Charts exploiting techniques from process algebra. This semantics is proposed for standardization within the ITU-TS. We start with the semantics of the core language of Message Sequence Charts, Basic Message Sequence Charts, and subsequent...

messages A message is completely determined by its sender instance, its receiver instance and its message identifier. Therefore, a message can be represented by a triple which consists of these three identifiers. Such a triple will be called an abstract message. A type Msg is defined from which the elements represent abstract messages. Definition 1 The type Msg is defined by Msg = L(!address?) \Theta L(!address?) \Theta L(!msgid?) In case of a message output event, the sender instance name is the name of the instance the message output is specified on. In case of a message input event, the receiver instance name is the name of the instance the message input is specified on. To obtain the name of an instance from its definition the function InstName is used. To obtain the address specification and the message identifier from a given communication event the functions Addr and MsgId are used. Their definitions can be found in Appendix A. Given the instance a communication event is spe...

We develop a formal semantics of sequence diagrams. The semantics is given in terms of our new temporal logic, named HDTL, which is designed to specify dynamically evolving systems. This approach allows to facilitate the generic feature of sequence diagrams as well as an automatic analysis, the identification of the instances of a sequence diagram over a trace.

Message Sequence Charts (MSCs) are a graphical language for scenarios of communicating components exchanging messages in a distributed environment. The language has been standardised by the International Telecommunication Union (ITU) and given a formal semantics by means of a process algebra. Nevertheless, little attention has been given to MSCs where a message with data is a building block. In this paper, we investigate the impact that the concept of data flow brings to the conventional semantics, and propose a CCS-like process calculus as an alternative formal framework. The proposed semantics captures the data flow properties while maintaining the expressiveness of the conventional semantics. Equivalence of MSCs is also discussed from the perspective of the corresponding process equivalence.

The purpose of this document is to formally define the syntax requirements of Message Sequence Charts. The description of the syntax requirements as presented in Recommendation Z.120 [IT93] is open to ambiguous interpretation and should therefore be reconsidered. A new set of syntax requirements is formulated and their formalization is presented. This formalization is based on