The general term is **analogy**.

From [Wikipedia](http://en.wikipedia.org/wiki/Analogy):

> In ancient Greek the word αναλογια (analogia) originally meant
> proportionality, in the mathematical sense, and it was indeed
> sometimes translated to Latin as proportio. From there analogy was
> understood as identity of relation between any two ordered pairs,
> whether of mathematical nature or not. Kant's Critique of Judgment
> held to this notion. Kant argued that there can be exactly the same
> relation between two completely different objects. The same notion of
> analogy was used in the US-based SAT tests, that included "analogy
> questions" in the form "A is to B as C is to what?" For example, "Hand
> is to palm as foot is to ____?" These questions were usually given in
> the Aristotelian format:
> 
> HAND : PALM : : FOOT : ____ 
> 
> While most competent English speakers will
> immediately give the right answer to the analogy question (sole), it
> is more difficult to identify and describe the exact relation that
> holds both between hand and palm, and between foot and sole[citation
> needed][original research?]. This relation is not apparent in some
> lexical definitions of palm and sole, where the former is defined as
> the inner surface of the hand, and the latter as the underside of the
> foot. Analogy and abstraction are different cognitive processes, and
> analogy is often an easier one.
> 
> It's important to note that the above analogy is not comparing all the
> properties between a hand and a foot, but rather comparing the
> relationship between a hand and its palm to a foot and its sole.
> While a hand and a foot have many dissimilarities, the analogy is
> focusing on their similarity in having an inner surface.

lovanda at [Wordreference.com](http://forum.wordreference.com/showthread.php?t=2183371) adds:

> Grammatically  A is to B as C is to D and  A is to B what C is to D
> are both correct.