void Database::processRule(Rule* rule) {
//Find the relation in the list of schemes matching the head of the predicate
Relation* headRelation = getHeadRelation(rule);
//Get the list of predicates
std::vector<Predicate*> predicateList = rule->j;
//Create new relations from each predicate
std::vector<Relation*> relationList = getRelationList(predicateList);
//Natural join the relations from the predicates
Relation* newRelation = join(relationList);
//Project on the final relation; only keep columns matching variables in the rule head
std::vector<std::string> headVariables = getHeadVariables(rule->hpl);
newRelation = newRelation->project(headVariables);
//Find the relation in the database that matches the head of the rule
//Already done (it's headRelation)
//Rename attributes in the new relation so it matches the rule head's schema
newRelation = renameToMatch(headRelation, newRelation, headVariables);
//Union the new relation with the matching relation
headRelation = unionWith(headRelation, newRelation);
std::sort(headRelation->facts.begin(), headRelation->facts.end(), Relation::tupleCompare);
}
bool RecursiveClauses::computeIsRecursive(const AstClause& clause, const AstTranslationUnit& translationUnit) const {
const AstProgram &program = *translationUnit.getProgram();
// we want to reach the atom of the head through the body
const AstRelation* trg = getHeadRelation(&clause, &program);
std::set<const AstRelation*> reached;
std::vector<const AstRelation*> worklist;
// set up start list
for(const AstAtom* cur : clause.getAtoms()) {
auto rel = program.getRelation(cur->getName());
if (rel == trg) return true;
worklist.push_back(rel);
}
// process remaining elements
while(!worklist.empty()) {
// get next to process
const AstRelation* cur = worklist.back();
worklist.pop_back();
// skip null pointers (errors in the input code)
if (!cur) continue;
// check whether this one has been checked before
if (!reached.insert(cur).second) continue;
// check all atoms in the relations
for(const AstClause* cl : cur->getClauses()) {
for(const AstAtom* at : cl->getAtoms()) {
auto rel = program.getRelation(at->getName());
if (rel == trg) return true;
worklist.push_back(rel);
}
}
}
// no cycles found
return false;
}
