Example #1
0
  /**
   * * 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);
  }
Example #2
0
  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;
  }