For example, Agent and Instrumental Cause are often subjects (of verbs selecting animate and inanimate subjects respectively); Patients/Themes can be direct objects of transitive verbs and subjects of change of state verbs; Goal and Beneficiary can be passivised and undergo the dative alternation; Instrument and Comitative are expressed by the same preposition in many languages (see Levin and Rappaport Hovav (2005).)
most annotation schemes in NLP and linguistics assume that semantic role labels are atomic.