Towards a SDL-DEVS Simulator Multiparadigm simulation

In this paper, we present the first version of a simulator that allows executing models defined using Discrete Event System Specification and models defined using Specification and Description Language. Specification and Description Language (SDL) is a graphical language, standardized under the ITU Z.100 recommendation, widely used to represent telecommunication systems, process control and real-time applications in general. Discrete Event System Specification (DEVS) is a formalism widely used on the simulation field to represent Discrete Event Systems. The execution of the DEVS models is based on a transformation of the simulation model DEVS representation to an equivalent SDL representation. To do this, we propose a XML representation for the DEVS models, and a XML representation for SDL models. Also we implement an algorithm capable to perform this transformation. Keywords-simulation; formal language; SDL; DEVS I. SPECIFICATION AND DESCRIPTION LANGUAGE Specification and Description Language (SDL) is an objectoriented, formal language defined by the International Telecommunication Union – Telecommunication Standardization Sector (ITU–T). The recommendation that summarizes its use is Z.100. The language is designed to specify complex, event-driven, real-time, interactive applications involving many concurrent activities using discrete signals to enable communication [1]. The definition of the model is based on different components: • Structure: system, blocks, processes and processes hierarchy. • Communication: signals, with the parameters and channels that the signals use to travel. • Behavior: defined through the different processes and procedures. • Data: based on Abstract Data Types (ADT). • Inheritances: to describe the relationships between, and specialization of, the model elements. The language has 4 levels (Figure 1), (i) System, (ii) Blocks, (iii) Processes and (iv) Procedures. To know more about the Specification and Description Language please refers to [2] [3] or Z.100 recommendation [1]. Figure 1: The first level of an SDL model. II. GRAPHICAL AND NO GRAPHICAL LANGUAGE SDL have two representations, SDL PR and SDL GR. SDLPR is conceived to be easily processed by computers, also allows a compact representation of a model, while SDL-GR has some textual elements which are identical to SDL-PR (this is to allow specification of data and signals) it is mainly graphical. Figure 2 shows an example of a textual and graphical representation of an SDL process. We are not using the textual version of SDL only for one reason. Some different textual representations of DEVS based on XML format exist. Since we want to allow an automatic transformation from SDL to DEVS, the use of XML simplifies our programming code because now is easy to read and write structured text files that follow the XML syntax, and also, thanks to the XSD we can validate the correctness of its syntax. We are using the XML representation for SDL proposed in [4]. Since the more important aspects of an XML file can be represented, and validated, through an XSD file, in the next section some areas of the XSD file are shown. process P; start; nextstate idle; state idle; input s; output t; nextstate idle; endstate idle; endprocess P; Figure 2: textual and graphical SDL representation A. XML representation of an SDL simulation model This representation was first presented on [5], no modifications have been done from this schema. We next describe the more important elements. For further details, please see [5], or download the complete schema from [6]. Figure 3. XSD schema, system view Figure 4. XSD schema, process view In Figure 3 we show the first level of the XSD schema we use to validate the structure of our XML. The first level of this schema represents the first level of the Specification and Description Language (system outmost block). Figure 4 shows the process type that allows represent an SDL process.