Relations do well for common connections in the language, but sometimes more is required -
A Section 14 charge
A human papillomavirus
Dinner at Iguana Joe's
A noun phrase is assembled and used to reference a complex object, which is often a process. Relations can be used to describe parts of the process, but the process itself is not a verb - its "parameters" need to be referenced through verbs or prepositions, with the complex object lurking behind the text, and understood by writer and reader. We need to do the same for the automated reader.
A similar mechanism had been built into Orion - we called it subnets, an equivalent would be an undirected user defined function. The parameters of the function have no sense of order, as a relation like ToSell has, with its ordering of Seller, Thing Sold and Buyer (ToSell itself is a shell function - it hides the process of the simultaneous change of ownership of the two parties involved in the sale).
As the diagram suggests, shelling can occur at many levels.