Prolog - The Solar System.

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Prolog is excellent for queries on relational data (as in the Mathematical sense of a "relation"), e.g.,
orbits(mercury, sun).  {facts}
orbits(venus,   sun).
orbits(earth,   sun).
orbits(mars,    sun).
orbits(jupiter, sun).
orbits(saturn,  sun).
orbits(uranus,  sun).
orbits(neptune, sun).

orbits(moon, earth).

orbits(deimos, mars).
orbits(phobos, mars).

orbits(ganymede, jupiter).
orbits(callisto, jupiter).
orbits(io,       jupiter).
orbits(europa,   jupiter).

orbits(titan,     saturn).
orbits(enceladus, saturn).

orbits(titania, uranus).
orbits(oberon,  uranus).
orbits(umbriel, uranus).
orbits(ariel,   uranus).
orbits(miranda, uranus).

orbits(triton, neptune).

planet(P)    <= orbits(P, sun).     {rules}
satellite(S) <= orbits(S, P) and planet(P).

? satellite(S).   {query}

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