A fundamental aspect which affects the efficiency and the performance of Service-Oriented Architectures is the mechanism which allows to manage sessions and, in particular, to assign incoming messages to the correct sessions (also known as service instances). A relevant mechanism for solving this problem, first introduced by BPEL and then used in other languages (e.g. Jolie) is that one based on correlation sets. The BPEL and Jolie languages are currently allowing the use of messages whose target is only one session. However there are a lot of scenarios where being able to send a broadcast message to more than one session could be useful. Supporting such a broadcast primitive means to allow correlation sets which can contain unspecified variables and this can be very inefficient, since usual implementations in terms of hash tables cannot be used in this case.In this paper we propose a data structure, based on radix trees and an algorithm for managing a correlation mechanism that supports the broadcast primitive, without degrading the performances.