Include ModelJoin support in main development

This will merge the completed ModelJoin abstraction as well as an ANTLR based parser to our main development branch. Afterwards we can start with adding custom views for the Sync UI.

src/main/java/org/rosi_project/model_sync/model_join/representation/grammar/JoinExpression.java

@@ -22,6 +22,8 @@ import org.rosi_project.model_sync.model_join.representation.core.ClassResource;
  *
  * @author Rico Bergmann
  * @see NaturalJoinExpression
+ * @see OuterJoinExpression
+ * @see ThetaJoinExpression
  */
 public abstract class JoinExpression implements Iterable<KeepExpression> {
 
@@ -32,6 +34,8 @@ public abstract class JoinExpression implements Iterable<KeepExpression> {
 
     /**
      * The {@code natural join} combines two classes based on attributes with equal name and type.
+     *
+     * @see NaturalJoinExpression
      */
     NATURAL,
 
@@ -39,12 +43,16 @@ public abstract class JoinExpression implements Iterable<KeepExpression> {
      * The {@code outer join} works like the {@link #NATURAL} one, but leaves instances from one
      * class with no corresponding instance in the other class according to the {@code outer join
      * type}. See the subclass for details.
+     *
+     * @see OuterJoinExpression
      */
     OUTER,
 
     /**
      * The {@code theta join} is more general than the {@link #NATURAL} and {@link #OUTER} one as
      * it enables an arbitrary criteria to define whether two instances are "joinable" or not.
+     *
+     * @see ThetaJoinExpression
      */
     THETA
   }