Is there a sensible classification of the properties of structures with a given signature $\sigma$, e.g. graphs with $\sigma = \lbrace R \rbrace$?
For example like this:
properties defined by first-order sentences over $\sigma$ (with or without specific syntactical properties)
properties defined by monadic second-order sentences over $\sigma$ (with or without specific syntactical properties)
properties stating the existence of another structure (of the same kind or another) and a specific
mappingrelation to itproperties stating that a given structure invariant has a specific value
properties stating that a given structure invariant has a specific property
How can this list be expanded, can it be completed or can it never be exhaustive?