// This exercise was designed to maximaze the use of modules.  There
// is no reason to create som many modules under normal circumstances.
// Exessive use of modules complicates queries, as can be seen from
// the queries below.

// load modules
?- [employee >> employees],
	[division >> divisions],
	[company >> companies],
	[project >> projects].

// ?- Method[%mustDefine(on)]@\sys.

//  Queries


// Projects that have employees who work for company divisions
// that are different from the project's division.
?- ?:project[name->?P,
	     participants-> ?_E[division->?_EDiv]@employees,
	     division->?_PDiv]@projects,
   ?_EDiv != ?_PDiv.

// The names of all divisions that have the lowest average
// salary per employee among all the divisions of the same company
?- ?Div:division[name->?_N]@divisions,
   avg{?_Sal| ?_Sal = (?Div.employees@divisions).salary@employees}
   = 
   min{?_AvgSal|
	  ?_AvgSal = avg{?_Sal[?_Div1]|
	                  ?:company[divisions->{?Div,?_Div1}]@companies,
	                  ?_Sal= (?_Div1.employees@divisions).salary@employees}
      }.


// Type checking constraints
// We deliberately set the data so as to violate some typing constraints
type_error(?O,?M,?V) :-
	// value of wrong type
	(?O[?M->?V], ?O[?M=>?D])@?_Mod, \naf ?V:?D@?_Mod2
        ;
	// value exists, but type doesn't
	(?O[?M->?V], \naf ?O[?M=>?D])@?_Mod.

// ?- type_error(?O,?M,?V).

// Type checking using the _typecheck module
// ?- Type[%check(?[?=>?]@?, ?Violations)]@_typecheck.
/* Answers:
   ?Violations = (${bob[projects -> f1]@employees}, ${bob[projects => project]@employees})

   ?Violations = (${d1[employees -> mary]@employees}, ${d1[employees => employee]@employees})

   ?Violations = (${john[division -> d3]@employees}, ${john[division => division]@employees})

*/