P.B.Ladkin and S.Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....called the CCITT) The standard defines the allowed syntactic constructs rigorously, and is also accompanied by a formal semantics [35] that provides unambiguous meaning to basic MSCs in a process algebraic style. Other efforts at defining a rigorous syntax and semantics for MSCs have been made [10, 17, 29], and some tools supporting their analysis are available [1, 2, 6] Surprisingly, despite the widespread use of the charts themselves and the more rigorous foundational efforts cited above, several fundamental issues have been left unaddressed. One of the most basic of these is, quoting [7] ....

P.B. Ladkin and S. Leue, "Interpreting message flow graphs," Formal Aspects of Computing, Vol. 7, No. 5, pp. 473--509, 1995.

....second order logic MSO(P,B) interpreted over B bounded MSCs. We then show that B bounded regular MSC languages are exactly those that are definable in MSO(P,B) In related work, a number of studies are available which are concerned with individual MSCs in terms of their semantics and properties [1, 12]. As pointed out earlier, a nice way to generate a collection of MSCs is to use an MSG. A variety of algorithms have been developed for MSGs in the literature for instance, pattern matching [13, 17, 19] and detection of process divergence and non local choice [3] A systematic account of the ....

....to r s # is # # p q, r s # # p q = r s 1 , which is not a regular 20 string language. Recall that regular languages are closed under arbitrary projections. A number of studies are available which are concerned with individual MSCs in terms of their semantics and properties [1, 12]. The rest of the work in the area consists of checking specific properties of communication scenarios specified as MSGs. We briefly survey these results here. Muscholl, Peled, and Su [19] investigate various matching problems for MSCs and MSGs, where matching denotes embedding one partial order ....

Ladkin, P. B., Leue, S.: Interpreting message flow graphs. Formal Aspects of Computing 7(5) (1995) 473--509

....adapts, as an example, the all uses criterion to extended message flow graphs. Section 4 concludes the paper. 2 EXTENDED MESSAGE FLOW GRAPH OF A SPECIFICATION 2. 1 Definitions The proposed model for an SDL specification is an extended message flow graph (EMFG) based on message flow graphs (MFG) [Lad94]. Both MFG and EMFG are graphs representing concurrent processes exchanging messages. An MFG focuses on the communication behavior and control dependencies between processes and ignores pure computation statements inside processes, whereas an EMFG is capable of representing both control and data ....

P.B. Ladkin and S. Leue, "Interpreting message flow graphs", Formal Aspects of Computing, 1994.

....here, serves several purposes. First, it unambiguously defines the meaning of an MSC by interpreting an MSC in the mathematical model of transition graphs. Next, it allows for a good comparison to alternative semantics definitions of MSC, such as approaches based on Petri nets [9] Buchi automata [17], process algebra [19,25] and partial orders [1] Moreover, it enables a comparison to other languages for the description of distributed systems, such as SDL [12] and LOTOS [7] which are also provided with an operational semantics. Finally, an operational semantics is useful for the development ....

P.B. Ladkin and S. Leue. Interpreting message flow graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

.... e 2 e 4 e 5 e 1 e 3 P 2 oe m 1 [1; 2] e 7 e 8 e 6 e 9 P 3 oe oe oe Delta Delta A A A A Delta Delta T3:1 m 2 m 4 e 11 e 12 e 13 e 10 e 14 Figure 2: A basic MSC of control within each process in the MSC along with a causal dependency between the events of sending and receiving a message [2,6]. For facilitating the specifications of real time systems, several mechanisms have been introduced to describe timing constraints in MSCs, which are timers [4] interval delays [1] and timing marks [5] There have been several detailed discussions on timers and interval delays in [1,2,3] In ....

P.B. Ladkin and S. Leue. Interpreting Message Flow Graphs. In Formal Aspects of Computing, 7(5):473-509, 1995.

....In the standard, the semantics of MSCs is given via a translation, originally developed in [10] transforming the textual representation of MSCs into a process algebra, based on [1] for which an axiomatic semantics exists. Other semantics based on Petri nets or Buchi automata can be found in [8, 7, 5]. However, the standard process algebra semantics does not capture a specific feature of MSCs called conditions. Conditions are a rudimentary form of MSC composition: Within an MSC document (a collection of MSC diagrams) a condition describes possible continuation points of system behaviour. ....

P. Ladkin and S. Leue. Interpreting message flow graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

....Semantics for Message Sequence Chart Documents via a translation, originally developed in [14] transforming the textual representation of MSCs into a process algebra, based on [1] for which an axiomatic semantics exists. Other semantics based on Petri nets or Buchi automata can be found in [11, 13, 7]. However, the standard process algebra semantics does not capture a specific feature of MSCs called conditions. Conditions are a rudimentary form of MSC composition: Within an MSC document (a collection of MSC diagrams) a condition describes possible continuation points of system behaviour. ....

P.B. Ladkin and S. Leue. Interpreting message flow graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

....semantics of MSCs is given via a translation, which was originally developed in [MR94] It transforms the textual representation of MSCs into a process algebra, based on [BW90] for which an axiomatic semantics exists. Other semantics based on Petri nets or Buchi automata can be found in [LL94, LL95b, GRG93] However, the standard process algebra semantics does not capture a specific feature of MSCs called conditions. Conditions are a rudimentary form of MSC composition: Within an MSC document (a collection of MSC diagrams) a condition describes possible continuation points of system ....

P.B. Ladkin and S. Leue. Interpreting message flow graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

....= s 0 ; t 0 ) the following condition holds: s j= SDL P o j= MTL M: Similar conditions apply to the use of PTL and PMTL as complemenatary specifications in the context of SDL and MSC. 4. A state transition Model for Message Sequence Charts A finite state semantics for MSCs. In [LL94a] [LL94b] we defined a finite control state semantics for Message Flow Graphs (MFGs) Message Sequence Charts (MSC) CCI92b] are a particular sort of MFG. For an example of an MSC with so called conditions see Figure 1. The semantics works as follows. The graphical device MSC (left in Figure 1) is first ....

....edges, where a control flow edge being in the GSS indicates where the control of the respective process lies, and a message flow edge in the GSS indicates a message sent but not yet received. In the example of Figure 1 the GSS S1 corresponds to the set f(w; y) x; z)g. The semantics in [LL94a] [LL94b] defines a set of rules for enabling of events and for a GSS transition relation. In S1 the event y is enabled and when executed the system transits to state S2 = f(y; y) y; a) x; z)g. The result is a global state transition graph as on the right hand side of Figure 1. By defining an ....

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P.B. Ladkin and S. Leue. Interpreting message flow graphs. Formal Aspects of Computing, 1994. To appear. S. Leue

.... They also claim to be able to give (in other work) a complete algebraic semantics for Message Sequence Charts [MR94, Section 1] We have done more extensive work than reported in [MR94] summarised in [LL94] which they reference, based on calculating the global states described by an MSC [LL92][LLar]. For Basic MSCs, this calculation is very easy. However, our attempts to compare their work with ours met with some difficulties, which we explain here. ffl Firstly, the textual definition which Mauw and Reniers use does not suffice to describe Basic Message Sequence Charts. In [LL95] also ....

....They became aware of our work during its presentation to the CCITT (now ITU TS) Q.MSC standards committee meeting in Geneva in November 1992, which Mauw attended, when [LL92] was distributed and accepted as input document WD 3 13. Mauw and Reniers have not yet addressed the work in [LL92] LL94] [LLar], and have not offered their own comparison. We hope, however, that they will clarify the technical problems we have raised regarding their approach, to enable us or others to make the necessary comparison. ....

P. B. Ladkin and S. Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, To appear.

....branch describes a repeated request to establish the connection. The non iterating branch describes a successful connection establishment. The semantics of an MSC essentially consists of sequences (or traces) of messages that are sent and received among the concurrent processes in the MSC [14]. The order of communication events (i.e. message sent or received) in a trace is deduced from the visual partial order determined by the flow of control within each process in the MSC along with a causal dependency between the events of sending and receiving a message. To facilitate the ....

....is executed. Therefore, we need to resolve the association of the timeout event in M3 with the timer setting events. The choice affects the possible behavior of the MSC specification, i.e. its timing consistency analysis. Let us consider a uniform treatment of timers and events: The semantics in [14] intreprets events such that multiple sends of a message are deactivated by one receive of the message, based on an argument showing that MSC specifications are finite state devices 1 . In the case of timers, this translates to associating the timeout event with any of the two timer setting ....

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P. B. Ladkin and S. Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

....operators facilitate the specification of large scale systems. In addition, MSCs offer essential constructs in a requirements language for reactive systems, e.g. distinction between the system and its environment, communication exchanges, internal actions, and timers along a formal semantics [16, 18]. As a design language, the notion of processes in MSCs along the composition operators can be used to reflect a software architecture. However, iteration and nondeterminism in MSCs require additional, explicit information, e.g. underlying network architecture and interprocess synchronization to ....

....sent and received among the concurrent processes in the MSC. The order of communication events (i.e. message sent or received) in a trace is deduced from the visual flow of control within each process in the MSC along with a causal dependency between the event of sending and receiving a message [18]. Message Sequence Charts offer several advantages to the requirements and design phases of the development of reactive systems. One is the intuitive, graphical notation of MSCs which helps a designer to visualize the system s structure and interfaces. In addition, as a requirements specification ....

P. B. Ladkin and S. Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

.... methodologies [RBP 91, Jea92, SGW94] tools to analyse the design of message exchanges at early stages in the software lifecycle [Hol96, AHP96] and methods describing design patterns [BMR 96] In previous work we defined a finite state semantics for Message Sequence Charts [LL95b] and discussed in [LL95a] implications of the MSC notation as 1991 Mathematics Subject Classification. Primary 68Q60, 68Q55, 68Q10; Secondary 68N99, 03B45. The first author was supported in part by the National Science and Engineering Research Council of Canada (NSERC) 1 2 STEFAN LEUE AND ....

....above and below. P1 sends a message of type a to P2, which (asynchronously) receives it, and then sends a message of type b to P1, which (asynchronously) receives it. This example should suffice to understand what BMSCs are supposed to mean. BMSCs do not have any branching or iteration. In [LL95b] we described how to represent BMSCs algebraically as so called basic Message Flow Graphs (MFGs) and then translated MFGs into (global ) state machines. We are not primarily interested in BMSCs here since their meaning is straightforward and implementation is trivial. We concern ourselves with ....

[Article contains additional citation context not shown here]

P. B. Ladkin and S. Leue, Interpreting Message Flow Graphs, Formal Aspects of Computing 7 (1995), no. 5, 473--509.

....operators facilitate the specification of largescale systems. In addition, MSCs offer essential constructs in a requirements language for reactive systems, e.g. distinction between the system and its environment [26] communication exchanges, internal actions, and timers along a formal semantics [18, 20]. As a design language, the notion of processes in MSCs along the composition operators can be used to reflect a software architecture. However, iteration and nondeterminism in MSCs require additional, explicit information, e.g. underlying network architecture and interprocess synchronization to ....

....sent and received among the concurrent processes in the MSC. The order of communication events (i.e. message sent or received) in a trace is deduced from the visual flow of control within each process in the MSC along with a causal dependency between the event of sending and receiving a message [20]. Message Sequence Charts offer several advantages to the requirements and design phases of the development of reactive systems. One is the intuitive, graphical notation of MSCs which helps a designer to visualize the system s structure and interfaces. In addition, as a requirements specification ....

P. B. Ladkin and S. Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995. 16

..... 15 4.3 Implementation in Mesa . 18 5 Use of Synthesized Models 18 6 A complex example: GSM Mobility Management 20 7 Conclusion 23 A Formal Representation of the Synthesis Process i A. 1 Formal Definition of MSCs (from [5, 20]) i A.2 Formal Definition of ROOM Model . i B Algorithms ii B.1 Algorithm for Structure Synthesis . ii B.2 Maximum Progress Algorithm for ....

....HMSC graph. We will call the collection of an HMSC graph and the referenced bMSCs an MSC specification. MSC specifications specify partially ordered event sequences. A number of approaches to formalizing MSCs and defining their semantics have been proposed. We will use the formalization given in [20] within the remainder of this paper. The TOASTER example. For illustrative purposes we developed the TOASTER example MSC specification, c.f. Figure 2. The specification consists of the HMSC TOASTER which describes the composition of bMSCs IDLE, EJECT, ERROR, START and TOAST. Each of the bMSCs ....

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P. B. Ladkin and S. Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473-- 509, 1995.

....Therefore, we need to resolve the association of the one timeout event in M3 with the two timer setting events. The choice obviously affects the timing consistency analysis. Let us try to derive the semantics of repeatedly invoked timers from that of repeatedly sent messages. Ladkin and Leue (Ladkin Leue 1995) use a finite state argument to interpret multiple sends of a message as deactivated by one receive of the message. At the time of writing Z.120 does not deal with the semantics of iterating system behavior. In the case of timers, this interpretation translates into associating the timeout event ....

....3) a temporal edge (x; y) connects a timer setting event x with a timer reset or timeout 10 Timing Constraints in Message Sequence Chart Specifications event y. The label of an edge is the timing delay and for a signal edge the message type in addition. For details, the reader is referred to (Ladkin Leue 1995) where basic MSCs without timing constraints are represented as Message Flow Graphs. This translation is easily augmented with the temporal edges to represent timing constraints. Given a bMSC M , its temporal graph T g (M) is obtained as follows: ffl Each node in M is represented by a node in T ....

Ladkin, P. B. & Leue, S. (1995), `Interpreting Message Flow Graphs', Formal Aspects of Computing 7(5), 473--509.

.... and environments [23, 14] Object oriented methodologies [24, 13, 26] tools to analyse the design of message exchanges at early stages in the software lifecycle [10, 2] and methods describing design patterns [5] In previous work we defined a finite state semantics for Message Sequence Charts [16], and discussed in [15] implications of the MSC notation as defined in Z.120. Although Basic MSCs look simple, syntactic features such as conditions or branchings which are defined for High level MSCs can make it harder to figure out what these latter describe and automated help is desirable. We ....

....above and below. P1 sends a message of type a to P2, which (asynchronously) receives it, and then sends a message of type b to P1, which (asynchronously) receives it. This example should suffice to understand what BMSCs are supposed to mean. BMSCs do not have any branching or iteration. In [16] we described how to represent BMSCs algebraically as so called basic Message Flow Graphs (MFGs) and then translated MFGs into (global ) state machines. We are not primarily interested in BMSCs here since their meaning is straightforward and implementation is trivial. We concern ourselves with 2 ....

[Article contains additional citation context not shown here]

P. B. Ladkin and S. Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

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P.B.Ladkin and S.Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

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Leue, P.; Ladkin, S.: Interpreting Message Flow Graphs. In Formal Aspects of Computing, 1995

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P.B.Ladkin and S.Leue. Interpreting Message Flow Graphs. Formal Aspects of Computing, 7(5):473--509, 1995.

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Ladkin, P. B., Leue, S.: Interpreting message flow graphs. Formal Aspects of Computing 7(5) (1995) 473--509

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P. B. Ladkin and Stefan Leue. "Interpreting Message Flow Graphs". Formal Aspects of Computing 7(5), p. 473 - 509, Sept./Oct. 1995.

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P.B. Ladkin, S. Leue, Interpreting message flow graphs, Formal Aspects Comput. 3 (1994).

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P. B. Ladkin and S. Leue, Interpreting Message Flow Graphs, Formal Aspects of Computing, 7(5):473-509, 1995.

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P.B. Ladkin and S.Leue. Interpreting Message Flow Graphs, Formal Aspects of Computing 7(5), p. 473 - 509, Sept./Oct. 1995.

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