The semantic structure is the structure of the language (or the independent thing between languages). This does not automatically facilitate machine Understandable knowledge. You would need to write the code to understand it first, which is probably almost as difficult as understanding English for example.

Only when relations are defined in a kind of Prolog style in those examples it will be usable as knowledge about things other than language.

A computer might spit out texts which it guessed are connected to some question you ask it though. Does not mean it understands the relations of things.

But when can we ever really say "a machine understands" something? So perhaps there is not much of a difference?