When participating in activities in a collaborative digital environment, people leave traces. Such traces in return can be used for recommending somebody regarding his/her competency on a given concept. Doing so improves further collaboration because knowing users' specialties ameliorates distributing tasks reasonably. In this article we propose a semantic model taking into account the concepts of activity, trace of interaction and competency. Applying Logistic Regression, we exploit this model to offer recommendation of a competent person in a digital ecosystem.