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(moon, earth).

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

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

? satellite(S).   {query}

Apparently this was used in question 24 'Evolution of Programming Languages', in Section III of 'Software Design and Development', 2010 Higher School Certificate Examination, NSW.

Coding Ockham's Razor, L. Allison, Springer

A Practical Introduction to Denotational Semantics, L. Allison, CUP

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© L. Allison   (or as otherwise indicated),
Faculty of Information Technology (Clayton), Monash University, Australia 3800 (6/'05 was School of Computer Science and Software Engineering, Fac. Info. Tech., Monash University,
was Department of Computer Science, Fac. Comp. & Info. Tech., '89 was Department of Computer Science, Fac. Sci., '68-'71 was Department of Information Science, Fac. Sci.)
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