  Probabilistic models require the notion of event space for defining a
probability measure. An event space has a probability measure which ensues the
Kolmogorov axioms. However, the probabilities observed from distinct sources,
such as that of relevance of documents, may not admit a single event space thus
causing some issues. In this article, some results are introduced for ensuring
whether the observed prob- abilities of relevance of documents admit a single
event space. More- over, an alternative framework of probability is introduced,
thus chal- lenging the use of classical probability for ranking documents. Some
reflections on the convenience of extending the classical probabilis- tic
retrieval toward a more general framework which encompasses the issues are
made.
