DecompositionToBCNF.java

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 * Copyright: GPL v3                                                          *
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package dbaCore.logic.normalization;

import dbaCore.data.Attribute;
import dbaCore.data.FunctionalDependency;
import dbaCore.data.NormalizationResult;
import dbaCore.data.RelationSchema;
import dbaCore.logic.Analysis.RelationUtils;

import java.util.ArrayList;

/**
 * Normalization to BoyceCodd-NormalForm using Decomposition
 *
 * @author Sebastian Theuermann
 */
public class DecompositionToBCNF extends Decomposition {

  @Override
  public void normalize(RelationSchema relationToNormalize, NormalizationResult result, Boolean minimizeFds) {

    if (minimizeFds) {
      normalizeRelation(getMinimalRelation(relationToNormalize), result);
    } else {
      normalizeRelation(relationToNormalize, result);
    }

  }

  private void normalizeRelation(RelationSchema relationToNormalize, NormalizationResult result) {

    RelationSchema newSchema;

    ArrayList<FunctionalDependency> violatingFds = checker.checkForBCNF(relationToNormalize);
    FunctionalDependency violatingFd;

    // If there is no FD violating BCNF ==> nothing to do here
    if (relationToNormalize.getFunctionalDependencies().isEmpty() || violatingFds.isEmpty()) {
      // Remove duplicate entry of relation in results
      for (RelationSchema relation : result.getRelations()) {
        if (relation.equals(relationToNormalize)) {
          result.getRelations().remove(relation);
          break;
        }
      }
      result.getRelations().add(relationToNormalize);
      return;
    }

    // FD Y ==> A violates BCNF
    newSchema = new RelationSchema();
    newSchema.setName(RelationUtils.getInstance().getRelationName(relationToNormalize.getName(),
      result.getRelations()));

    ArrayList<Attribute> onlyDeterminedAttributes = checker.getOnlyDeterminedAttributes(relationToNormalize);
    violatingFd = violatingFds.get(0);
    for (FunctionalDependency fd : violatingFds) {
      if (onlyDeterminedAttributes.containsAll(fd.getTargetAttributes())) {
        violatingFd = fd;
        break;
      }
    }

    // S2 = YA
    // S1 = S - A
    transferFd(relationToNormalize, newSchema, violatingFd);

    // Update keys
    updatePrimaryAndForeignKeys(relationToNormalize, newSchema, result.getForeignKeys());

    // Recursive calls
    normalizeRelation(newSchema, result);
    normalizeRelation(relationToNormalize, result);
  }

  /**
   * Moves a FD and it's Attributes from one RelationSchema to another
   *
   * @param oldSchema the RelationSchema to cut from
   * @param newSchema the RelationSchema to paste into
   * @param fd        the FunctionalDependency to move
   */
  private void transferFd(RelationSchema oldSchema, RelationSchema newSchema, FunctionalDependency fd) {

    oldSchema.removeFunctionalDependency(fd);

    // Copy everything to new schema
    for (Attribute sourceAttribute : fd.getSourceAttributes()) {
      newSchema.addAttribute((Attribute) sourceAttribute.getClone());
    }
    for (Attribute targetAttribute : fd.getTargetAttributes()) {
      newSchema.addAttribute((Attribute) targetAttribute.getClone());
    }
    newSchema.getFunctionalDependencies().add(fd.getClone());

    // reconnect attributes with functional dependencies
    newSchema.restoreReferences();

    // Remove copied things in the old schema
    oldSchema.getAttributes().removeAll(fd.getTargetAttributes());

    ArrayList<FunctionalDependency> fdsToDelete = new ArrayList<>();
    ArrayList<Attribute> attributesToDelete = new ArrayList<>();

    for (FunctionalDependency oldFd : oldSchema.getFunctionalDependencies()) {
      // Taking care of the TargetAttributes
      for (Attribute attr : oldFd.getTargetAttributes()) {
        if (!oldSchema.getAttributes().contains(attr)) {
          attributesToDelete.add(attr);
        }
      }

      while (!attributesToDelete.isEmpty()) {
        oldFd.getTargetAttributes().remove(attributesToDelete.get(0));
        attributesToDelete.remove(0);
      }

      if (oldFd.getTargetAttributes().isEmpty()) {
        fdsToDelete.add(oldFd);
      }

      // Taking care of the SourceAttributes
      for (Attribute targetAttr : oldFd.getSourceAttributes()) {
        if (fdsToDelete.contains(oldFd)) {
          continue;
        }
        if (!oldSchema.getAttributes().contains(targetAttr)) {
          fdsToDelete.add(oldFd);
        }
      }
    }

    for (FunctionalDependency candidate : fdsToDelete) {
      oldSchema.removeFunctionalDependency(candidate);
    }

    RelationUtils.getInstance().restoreAttributesByFds(oldSchema);

  }

}