No, never, Katerina. In any LCA model, a process has inputs and outputs which are flows, not processes. I am aware that some other LCA software (SimaPro) might confuse users a bit because it shows the products under a headline 'processes', but behind the user interface the logic is the same. The PEF database, as it is released, contains only system processes with very few exceptions, that are meant to be autonomous and fully aggregated and do not need any input product.
A process has a product, always, which can be a waste or product flow. Use this to link to another process.