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Top1. Introduction
A Telephone Switching System (TSS) is a complex real-time system (Thompson, 2000; McDermid, 1991; Wang, 2007, 2009). The functional structure of the TSS system can be described by a conceptual model as illustrated in Figure 1, which consists of four subsystems known as the call processing, subscribers, routes, and signaling subsystems.
Figure 1. Functional structure of the TSS system
In the conceptual model of the TSS system, its configuration encompasses 1 call processor and 16 subscribers. There are 5 internal switching routes and a set of 5 signaling trunks providing the dial, busy, ringing, ring-back, and special tones. The call processor modeled by a set of functional processes operates on the line scanners, call records, digits receivers, signaling trunks, system clock, and routes in order to implement a coherent program-controlled switching system.
An important finding in the basic research in software engineering is that any software system, including the hybrid hardware and software system can be rigorously modeled by a set of structural models, a set of process models, and their interactions (Hoare, 1978; Wang, 2002, 2007; Wang & King, 2000). The structure model (SM) is a rigorous abstraction and formal representation of the system’s architecture and components. The process model (PM) is a rigorous description of the system’s behaviors and operations onto the abstract SMs.
Definition 1. An abstract Structure Model (SM) is a generic architectural model for a software system, its internal control structures, and its interfaces with hardware components and external input/output, which can be rigorously modeled and refined as an n-tuple, i.e.:
(1)
where
Si, 1 ≤
i ≤
n, is a set and also a type of elements
e that share the property
pi.
Definition 2. An abstract Process Model (PM) of a program ℘ is a composition of a finite set of m embedded processes according to the time-, event-, and interrupt-based process dispatching rules,
, i.e.:
(2)
where
si and
sj are one of the 17 RTPA meta-processes,
rij is one of the 17 RTPA algebraic process operations, and
ek is a general, timing, or interrupt event.
This paper reports an empirical experiment on the implementation of the TSS system based on formal models of the system in RTPA for conceptual modeling, system interface design, and programming implementation. In the remainder of this paper, the architectural designs of TSS in term of the structure models (SMs) in both RTPA and UML are described in Section 2. The functional designs of TSS in term of the process models (PMs) in both RTPA and UML are elaborated in Section 3. A set of comparative experiments in the design and implementation of the TSS system by three groups is demonstrated in Section 4.
TopAs described in Definition 1, the structure model is a rigorous abstraction and formal representation of the architecture of a system and the layout of a component. This section formally describes the structure models of TSS at the hierarchical levels of system and components from the top down, before the process models of TSS can be rigorously elaborated in Section 3.