Reuse of software entities such as components or web services raise composition issues since, most of the time, they present mismatching behavioural interfaces. Here, we particularly focus on systems for which the number of transactions is unbounded, and unknown in advance. This is typical in pervasive systems where a new client may show up at any moment to request or access a specific service. Hence, we advocate for the use of the ?-calculus to specify component interfaces. The ?-calculus is particularly suitable for creating new component instances and channels dynamically. The unbounded number of transactions and the use of the ?-calculus obliges to apply the composition at run-time. In this paper, we propose a run-time composition engine that solves existing mismatches.