Adding Priority to Event Structures

TL;DR

This paper introduces a method to incorporate priority relations into various Event Structures, analyzing how priority interacts with existing relations and affecting the complexity of defining partial orders.

Contribution

It extends multiple types of Event Structures by adding priority relations and studies their interactions, providing a basis for more expressive event modeling.

Findings

Priority relations can be redundant in certain event structures.

Adding priority complicates the definition of partial orders.

The approach is exemplified on Prime, Bundle, Extended Bundle, and Dual ESs.

Abstract

Event Structures (ESs) are mainly concerned with the representation of causal relationships between events, usually accompanied by other event relations capturing conflicts and disabling. Among the most prominent variants of ESs are Prime ESs, Bundle ESs, Stable ESs, and Dual ESs, which differ in their causality models and event relations. Yet, some application domains require further kinds of relations between events. Here, we add the possibility to express priority relationships among events. We exemplify our approach on Prime, Bundle, Extended Bundle, and Dual ESs. Technically, we enhance these variants in the same way. For each variant, we then study the interference between priority and the other event relations. From this, we extract the redundant priority pairs-notably differing for the types of ESs-that enable us to provide a comparison between the extensions. We also exhibit that priority considerably complicates the definition of partial orders in ESs.