Teams of pushdown automata

Abstract

We introduce team pushdown automata (PDAs) as a theoretical framework capable of modelling various communication and cooperation strategies in complex, distributed systems. Team PDAs are obtained by augmenting distributed PDAs with the notion of team cooperation or, alternatively, by augmenting team automata with pushdown memory. In a team PDA, several PDAs work as a team on the input word placed on a common one-way input tape. At any moment in time one team of PDAs, each with the same symbol on top of its stack, is active: each PDA in the active team replaces the topmost symbol of its stack and changes state, while the current input symbol is read from the input tape by a common reading head. The teams are formed according to the team cooperation strategy of the team PDA and may vary from one moment to the other. Based on the notion of competence, we introduce a variety of team cooperation strategies. If all stacks are empty when the input word has been completely read, then this word is part of the language accepted by the team PDA. Here we focus on the accepting capacity of team PDA.

^†E-mail: [email protected]

^‡E-mail: [email protected]

Keywords:

• Pushdown automata
• Team cooperation
• Competence
• Accepting capacity
• Team automata

Acknowledgments

The first author was supported by an ERCIM postdoctoral fellowship and the third author was supported by the Centre of Excellence in Information Technology, Computer Science and Control, ICA1-CT-2000-70025, HUN-TING project, WP5. The first author's research for this article was fully carried out during his stay at the Computer and Automation Research Institute of the Hungarian Academy of Sciences.

Notes

^†E-mail: [email protected]

^‡E-mail: [email protected]