/**
* * Enforces all equalities in the query, that is, for every equivalence class (among variables)
* defined by a set of equalities, it chooses one representative variable and replaces all other
* variables in the equivalence class with the representative variable. For example, if the query
* body is R(x,y,z), x=y, y=z. It will choose x and produce the following body R(x,x,x).
*
* <p>We ignore the equalities with disjunctions. For example R(x,y,z), x=y OR y=z Note the
* process will also remove from the body all the equalities that are here processed.
*
* @param result
*/
public static void enforceEqualities(CQIE result) {
List<Function> body = result.getBody();
Substitution mgu = new SubstitutionImpl();
// collecting all equalities as substitutions
for (int i = 0; i < body.size(); i++) {
Function atom = body.get(i);
SubstitutionUtilities.applySubstitution(atom, mgu);
if (atom.getFunctionSymbol() == ExpressionOperation.EQ) {
if (!mgu.composeTerms(atom.getTerm(0), atom.getTerm(1))) continue;
body.remove(i);
i--;
}
// search for nested equalities in AND function
else if (atom.getFunctionSymbol() == ExpressionOperation.AND) {
nestedEQSubstitutions(atom, mgu);
// we remove the function if empty because all its terms were equalities
if (atom.getTerms().isEmpty()) {
body.remove(i);
i--;
} else {
// if there is only a term left we remove the conjunction
if (atom.getTerms().size() == 1) {
body.set(i, (Function) atom.getTerm(0));
}
}
}
}
SubstitutionUtilities.applySubstitution(result, mgu, false);
}
public DatalogProgram constructDatalogProgram() {
DatalogProgram datalog = dfac.getDatalogProgram();
LinkedList<String> errorMessage = new LinkedList<String>();
for (OBDAMappingAxiom axiom : mappingList) {
try {
// Obtain the target and source query from each mapping axiom in
// the model.
CQIE targetQuery = (CQIE) axiom.getTargetQuery();
// Get the parsed sql, since it is already parsed by the mapping
// parser
// consider also MetaMappingExpander
// VisitedQuery queryParsed = ...;
OBDASQLQuery sourceQuery = (OBDASQLQuery) axiom.getSourceQuery();
// Construct the SQL query tree from the source query
VisitedQuery queryParsed = translator.constructParser(sourceQuery.toString());
// Create a lookup table for variable swapping
LookupTable lookupTable = createLookupTable(queryParsed);
// We can get easily the table from the SQL
ArrayList<RelationJSQL> tableList = queryParsed.getTableSet();
// Construct the body from the source query
ArrayList<Function> atoms = new ArrayList<Function>();
for (RelationJSQL table : tableList) {
// Construct the URI from the table name
String tableName = table.getGivenName();
String predicateName = tableName;
// Construct the predicate using the table name
int arity = dbMetaData.getDefinition(tableName).countAttribute();
Predicate predicate = dfac.getPredicate(predicateName, arity);
// Swap the column name with a new variable from the lookup
// table
List<Term> terms = new ArrayList<Term>();
for (int i = 1; i <= arity; i++) {
String columnName =
dbMetaData.getFullQualifiedAttributeName(tableName, table.getAlias(), i);
String termName = lookupTable.lookup(columnName);
if (termName == null) {
throw new RuntimeException(
"Column '" + columnName + "'was not found in the lookup table: ");
}
Term term = dfac.getVariable(termName);
terms.add(term);
}
// Create an atom for a particular table
Function atom = dfac.getFunction(predicate, terms);
atoms.add(atom);
}
// For the join conditions WE STILL NEED TO CONSIDER NOT EQUI
// JOIN
ArrayList<Expression> joinConditions = queryParsed.getJoinCondition();
for (Expression predicate : joinConditions) {
Function atom = getFunction(predicate, lookupTable);
atoms.add(atom);
}
// For the selection "where" clause conditions
SelectionJSQL selection = queryParsed.getSelection();
if (selection != null) {
// Stack for filter function
Stack<Function> filterFunctionStack = new Stack<Function>();
Expression conditions = selection.getRawConditions();
Function filterFunction = getFunction(conditions, lookupTable);
filterFunctionStack.push(filterFunction);
// The filter function stack must have 1 element left
if (filterFunctionStack.size() == 1) {
Function filterFunct = filterFunctionStack.pop();
Function atom =
dfac.getFunction(filterFunct.getFunctionSymbol(), filterFunct.getTerms());
atoms.add(atom);
} else {
throwInvalidFilterExpressionException(filterFunctionStack);
}
}
// Construct the head from the target query.
List<Function> atomList = targetQuery.getBody();
// for (Function atom : atomList) {
Iterator<Function> atomListIter = atomList.iterator();
while (atomListIter.hasNext()) {
Function atom = atomListIter.next();
List<Term> terms = atom.getTerms();
List<Term> newterms = new LinkedList<Term>();
for (Term term : terms) {
newterms.add(updateTerm(term, lookupTable));
}
Function newhead = dfac.getFunction(atom.getPredicate(), newterms);
CQIE rule = dfac.getCQIE(newhead, atoms);
datalog.appendRule(rule);
}
} catch (Exception e) {
errorMessage.add(
"Error in mapping with id: "
+ axiom.getId()
+ " \n Description: "
+ e.getMessage()
+ " \nMapping: ["
+ axiom.toString()
+ "]");
}
}
if (errorMessage.size() > 0) {
StringBuilder errors = new StringBuilder();
for (String error : errorMessage) {
errors.append(error + "\n");
}
final String msg =
"There was an error analyzing the following mappings. Please correct the issue(s) to continue.\n"
+ errors.toString();
RuntimeException r = new RuntimeException(msg);
throw r;
}
return datalog;
}