# Revisiting local time semantics for networks of timed automata

## TL;DR

This paper improves reachability analysis in networks of timed automata by introducing a more efficient zone aggregation method using local time semantics, significantly reducing search space in many cases.

## Contribution

It presents a new algorithm leveraging local zones and fixes a termination flaw in existing methods for better efficiency in timed automata analysis.

## Key findings

- Order of magnitude reduction in search space on standard examples
- Algorithm performs comparably to standard methods on other examples
- Enhanced zone aggregation improves analysis efficiency

## Abstract

We investigate a zone based approach for the reachability problem in timed automata. The challenge is to alleviate the size explosion of the search space when considering networks of timed automata working in parallel. In the timed setting this explosion is particularly visible as even different interleavings of local actions of processes may lead to different zones. Salah et al. in 2006 have shown that the union of all these different zones is also a zone. This observation was used in an algorithm which from time to time detects and aggregates these zones into a single zone. We show that such aggregated zones can be calculated more efficiently using the local time semantics and the related notion of local zones proposed by Bengtsson et al. in 1998. Next, we point out a flaw in the existing method to ensure termination of the local zone graph computation. We fix this with a new algorithm that builds the local zone graph and uses abstraction techniques over (standard) zones for termination. We evaluate our algorithm on standard examples. On various examples, we observe an order of magnitude decrease in the search space. On the other examples, the algorithm performs like the standard zone algorithm.