While message sequence charts (MSCs) are widely used in industry to document the interworking of processes or objects, they are expressively weak, being based on the modest semantic notion of a partial ordering of events as defined, e.g., in the ITU standard. A highly expressive and rigorously defined MSC language is a must for serious, semantically meaningful tool support for use-cases and scenarios. It is also a prerequisite to addressing what we regard as one of the central problems in behavioral specification of systems: relating scenario-based inter-object specification to state-machine intra-object specification. This paper proposes an extension of MSCs, which we call live sequence charts (or LSCs), since our main extension deals with specifying "liveness", i.e., things that must occur. In fact, LSCs allow the distinction between possible and necessary behavior both globally, on the level of an entire chart and locally, when specifying events, conditions and progress over time within a chart. This makes it possible to specify forbidden scenarios, for example, and enables naturally specified structuring constructs such as subcharts, branching and iteration.

In this paper the most relevant issues of the standardization of the Message Sequence Chart (MSC) language within the CCITT Study Group X are discussed. The history of the new MSC recommendation Z.120 is sketched. Different types of diagrams which are closely related to MSCs are compared, since they build the basis for the MSC language. We distinguish these diagrams from the standardized MSC language by using the term Sequence Charts (SCs). Subsequently, the MSC language is introduced and several approaches towards a forthcoming formal MSC semantics are presented. 1 Introduction Sequence Charts (SCs) are a widespread means for the graphical visualization of selected system runs (traces) within communication systems. They can be viewed as a special trace language, which mainly concentrates on sending and consumption of messages by synchronously or asynchronously communicating processes. Obviously, main advantage of an SC is its clear graphical layout (e.g. fig. 1, 2), which immediately...

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.

syntax of HMSC A hierarchical graph is a mathematical structure that represents the information contents of an HMSC. The set HGid represents the set of all HMSC names. Obviously, this includes the names of BMSCs. Since we did not provide a formal graphical syntax for HMSC we cannot provide a formal mapping from HMSC to hierarchical graphs. However, the intuition is clear. A node in an HMSC contains a reference to another HMSC via its name. Definition 3.3.1 (Hierarchical graphs) A hierarchical graph is either a BMSC or a tuple #id, Nodes, Starts, Ends, Edges, l#, where . id # HGid is the name of the hierarchical graph; . Nodes, Starts, and Ends are pairwise disjoint sets of HMSC reference nodes, start nodes and end nodes respectively with Starts #= ?; . Edges # (Nodes # Starts) × (Nodes # Ends) is a set of edges. An edge (n, n # ) is denoted by n # n # ; . l : Nodes # HGid is a labeling function which associates to a node a reference to an HMSC by means of a...

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

We propose a semantics for Message Sequence Charts (MSCs). Our requirements are: to determine unambiguously which execution traces are allowed by an MSC; and to use a finite-state interpretation. Our semantics handles both synchronous and asynchronous communication. We define a global state automaton from an MSC, by first defining a transition system of global states, and from that a Buchi automaton. In using MSCs, properties of the environment and liveness properties of the MSC itself may be underspecified. We propose a method using temporal logic formulas to specify the required liveness properties. Keyword Codes: F.3.2; D.2.1; 2. Keywords: Semantics of Programming Languages; Requirements/Specifications; Protocol specification, testing and verification. 1. INTRODUCTION The purpose of this paper is to to propose a precise semantics for Message Sequence Charts (MSCs) [16]. Our interpretation also suffices to give a semantics for Time Sequence Diagrams [34]. We explain our semantics...

Message sequence charts (MSCs) are a standardised formalism for the specification of the system's communication behaviour that is widely used by industry. Various extensions to MSCs have recently been standardised by the ITU. This paper treats the extension of MSCs with structural operators that allow the hierarchical composition of MSCs. In particular, we propose a linear-time partial-order semantics for this extension that is based on the notion of partial-order multi-sets (pomsets, for short). We provide a compositional denotational semantics for hierarchical MSCs and show that well-known operations on pomsets correspond to the new composition operators in MSCs. The main benefit of our approach is that the semantics is conceptually rather straightforward, as opposed to the operational semantics for MSCs that is currently in the process of standardisation. Keywords Denotational semantics, partial-order multi-set, hierarchical MSC 1 INTRODUCTION In the telecommunication sector, MSC ...

In a Message Sequence Chart (MSC) the dynamical behaviour of a number of cooperating processes is depicted. An MSC defines a partial order on the communication events between these processes. This order determines the physical architecture needed for implementing the specified behaviour, such as a FIFO buffer between each of the processes. In a systematic way, we define 50 communication models for MSC and we define what it means for an MSC to be implementable by such a model. Some of these models turn out to be equivalent, in the sense that they implement the same class of MSCs. After analysing the notion of implementability, only ten models remain, for which we develop a hierarchy.

Message Sequence Charts (MSCs) are a graphical and textual language for the speci cation of message passing systems, in particular telecommunication systems. MSCs are standardised by the Internal Telecommunication Union in standard Z.120. Included in the standard is a formal semantics for MSCs by means of a process algebra. This semantics covers the complete language of single MSCs but lacks an interpretation for conditions which are used as continuation points of MSCs within an MSC document (a collection of MSCs). In this paper, we give a process algebraic semantics for basic MSCs including conditions, enabling the formal interpretation of entire MSC documents. 1

The World-Wide-Web is fast becoming a crucial medium for electronic commerce. Many companies are now involved in on-line retailing of goods and services to consumers through the Web. In some industries, business partnerships are being fostered in order to broaden the scope of their markets. One example is the telecommunications industry, where changes in business structure, spirited by deregulation, have resulted in alliances amongst different communications providers, including new players like the utilities and entertainment providers. In this environment, business processes may involve multiple co-operating entities and, supporting such interorganizational business processes can be achieved through the use of workflow management systems. In this paper, we present an approach for designing interorganizational workflows that supports co-operation of business partners, while preserving the autonomy of the partner organizations.