=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/expression/ExpressionService.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/expression/ExpressionService.java	2012-09-22 17:46:17 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/expression/ExpressionService.java	2012-09-22 21:59:39 +0000
@@ -56,7 +56,6 @@
     final String EXPRESSION_NOT_WELL_FORMED = "expression_not_well_formed";
     final String CONSTANT_DOES_NOT_EXIST = "constant_does_not_exist";
 
-
     final String DAYS_DESCRIPTION = "[Number of days]";
     final String NULL_REPLACEMENT = "0";
     final String SPACE = " ";
@@ -65,6 +64,7 @@
     final String OPERAND_EXPRESSION = "\\[\\d+?.*?\\]";
     final String DAYS_EXPRESSION = "[days]";
     final String CONSTANT_EXPRESSION = "\\[C(\\d+?)\\]";
+    final String COMPULSORY_PAIR_EXPRESSION = "[Compulsory]";
     
     /**
      * Adds a new Expression to the database.

=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/expression/Operator.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/expression/Operator.java	2011-12-26 10:07:59 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/expression/Operator.java	2012-09-22 21:59:39 +0000
@@ -34,7 +34,8 @@
     greater_than( ">" ), 
     greater_than_or_equal_to( ">=" ), 
     less_than( "<" ), 
-    less_than_or_equal_to( "<=" );
+    less_than_or_equal_to( "<=" ),
+    compulsory_pair( "[Compulsory pair]" );
 
     private final String mathematicalOperator;
 

=== modified file 'dhis-2/dhis-api/src/main/java/org/hisp/dhis/validation/ValidationResult.java'
--- dhis-2/dhis-api/src/main/java/org/hisp/dhis/validation/ValidationResult.java	2011-11-22 14:38:08 +0000
+++ dhis-2/dhis-api/src/main/java/org/hisp/dhis/validation/ValidationResult.java	2012-09-22 21:59:39 +0000
@@ -50,9 +50,9 @@
 
     private ValidationRule validationRule;
 
-    private double leftsideValue;
+    private Double leftsideValue;
 
-    private double rightsideValue;
+    private Double rightsideValue;
 
     // -------------------------------------------------------------------------
     // Constructors
@@ -63,7 +63,7 @@
     }
 
     public ValidationResult( Period period, OrganisationUnit source, ValidationRule validationRule,
-                             double leftsideValue, double rightsideValue )
+        Double leftsideValue, Double rightsideValue )
     {
         this.source = source;
         this.period = period;
@@ -189,22 +189,22 @@
         this.validationRule = validationRule;
     }
 
-    public double getLeftsideValue()
+    public Double getLeftsideValue()
     {
         return leftsideValue;
     }
 
-    public void setLeftsideValue( double leftsideValue )
+    public void setLeftsideValue( Double leftsideValue )
     {
         this.leftsideValue = leftsideValue;
     }
 
-    public double getRightsideValue()
+    public Double getRightsideValue()
     {
         return rightsideValue;
     }
 
-    public void setRightsideValue( double rightsideValue )
+    public void setRightsideValue( Double rightsideValue )
     {
         this.rightsideValue = rightsideValue;
     }

=== modified file 'dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/validation/DefaultValidationRuleService.java'
--- dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/validation/DefaultValidationRuleService.java	2012-09-22 18:42:59 +0000
+++ dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/validation/DefaultValidationRuleService.java	2012-09-22 21:59:39 +0000
@@ -33,7 +33,7 @@
 import static org.hisp.dhis.i18n.I18nUtils.getObjectsByName;
 import static org.hisp.dhis.i18n.I18nUtils.i18n;
 import static org.hisp.dhis.system.util.MathUtils.expressionIsTrue;
-import static org.hisp.dhis.system.util.MathUtils.getRounded;
+import static org.hisp.dhis.system.util.MathUtils.*;
 
 import java.util.Collection;
 import java.util.Date;
@@ -48,6 +48,7 @@
 import org.hisp.dhis.dataset.DataSet;
 import org.hisp.dhis.datavalue.DataValueService;
 import org.hisp.dhis.expression.ExpressionService;
+import org.hisp.dhis.expression.Operator;
 import org.hisp.dhis.i18n.I18nService;
 import org.hisp.dhis.organisationunit.OrganisationUnit;
 import org.hisp.dhis.period.Period;
@@ -256,20 +257,29 @@
                 if ( validationRule.getPeriodType() != null
                     && validationRule.getPeriodType().equals( period.getPeriodType() ) )
                 {
+                    Operator operator = validationRule.getOperator();
+                    
                     leftSide = expressionService.getExpressionValue( validationRule.getLeftSide(), valueMap, constantMap, null );
 
-                    if ( leftSide != null )
+                    if ( leftSide != null || Operator.compulsory_pair.equals( operator ) )
                     {
                         rightSide = expressionService.getExpressionValue( validationRule.getRightSide(), valueMap, constantMap, null );
 
-                        if ( rightSide != null )
+                        if ( rightSide != null || Operator.compulsory_pair.equals( operator )  )
                         {
-                            violation = !expressionIsTrue( leftSide, validationRule.getOperator(), rightSide );
-
+                            if ( Operator.compulsory_pair.equals( operator ) )
+                            {
+                                violation = ( leftSide != null && rightSide == null ) || ( leftSide == null && rightSide != null );
+                            }
+                            else
+                            {
+                                violation = !expressionIsTrue( leftSide, operator, rightSide );
+                            }
+                            
                             if ( violation )
                             {
                                 validationViolations.add( new ValidationResult( period, unit, validationRule,
-                                    getRounded( leftSide, DECIMALS ), getRounded( rightSide, DECIMALS ) ) );
+                                    getRounded( zeroIfNull( leftSide ), DECIMALS ), getRounded( zeroIfNull( rightSide ), DECIMALS ) ) );
                             }
                         }
                     }

=== modified file 'dhis-2/dhis-support/dhis-support-system/src/main/java/org/hisp/dhis/system/util/MathUtils.java'
--- dhis-2/dhis-support/dhis-support-system/src/main/java/org/hisp/dhis/system/util/MathUtils.java	2012-08-25 11:47:17 +0000
+++ dhis-2/dhis-support/dhis-support-system/src/main/java/org/hisp/dhis/system/util/MathUtils.java	2012-09-22 21:59:39 +0000
@@ -234,6 +234,17 @@
     }
     
     /**
+     * Returns 0d if the given value is null, the original value otherwise.
+     * 
+     * @param value the value.
+     * @return a double.
+     */
+    public static double zeroIfNull( Double value )
+    {
+        return value == null ? 0d : value;
+    }
+    
+    /**
      * Returns a random int between 0 and 999.
      */
     public static int getRandom()

=== modified file 'dhis-2/dhis-web/dhis-web-validationrule/src/main/resources/org/hisp/dhis/validationrule/i18n_module.properties'
--- dhis-2/dhis-web/dhis-web-validationrule/src/main/resources/org/hisp/dhis/validationrule/i18n_module.properties	2012-09-22 18:42:59 +0000
+++ dhis-2/dhis-web/dhis-web-validationrule/src/main/resources/org/hisp/dhis/validationrule/i18n_module.properties	2012-09-22 21:59:39 +0000
@@ -124,4 +124,5 @@
 specify_dataset=Please specify data sets
 analysing_please_wait=Analysing data, please wait
 skip_for_missing_values=Skip for missing values
-select_parameters=Select parameters
\ No newline at end of file
+select_parameters=Select parameters
+compulsory_pair=Compulsory pair
\ No newline at end of file

=== modified file 'dhis-2/dhis-web/dhis-web-validationrule/src/main/webapp/dhis-web-validationrule/addValidationRuleForm.vm'
--- dhis-2/dhis-web/dhis-web-validationrule/src/main/webapp/dhis-web-validationrule/addValidationRuleForm.vm	2012-07-26 11:14:41 +0000
+++ dhis-2/dhis-web/dhis-web-validationrule/src/main/webapp/dhis-web-validationrule/addValidationRuleForm.vm	2012-09-22 21:59:39 +0000
@@ -34,7 +34,8 @@
 				<option value="greater_than">$encoder.htmlEncode( $i18n.getString( "greater_than" ) )</option>
 				<option value="greater_than_or_equal_to">$encoder.htmlEncode( $i18n.getString( "greater_than_or_equal_to" ) )</option>
 				<option value="less_than">$encoder.htmlEncode( $i18n.getString( "less_than" ) )</option>
-				<option value="less_than_or_equal_to">$encoder.htmlEncode( $i18n.getString( "less_than_or_equal_to" ) )</option>			
+				<option value="less_than_or_equal_to">$encoder.htmlEncode( $i18n.getString( "less_than_or_equal_to" ) )</option>
+                <option value="compulsory_pair">$encoder.htmlEncode( $i18n.getString( "compulsory_pair" ) )</option>
 			</select>
 		</td>
 	</tr>

=== modified file 'dhis-2/dhis-web/dhis-web-validationrule/src/main/webapp/dhis-web-validationrule/updateValidationRuleForm.vm'
--- dhis-2/dhis-web/dhis-web-validationrule/src/main/webapp/dhis-web-validationrule/updateValidationRuleForm.vm	2012-07-26 11:30:34 +0000
+++ dhis-2/dhis-web/dhis-web-validationrule/src/main/webapp/dhis-web-validationrule/updateValidationRuleForm.vm	2012-09-22 21:59:39 +0000
@@ -43,6 +43,7 @@
 				<option value="greater_than_or_equal_to" #if ( $validationRule.operator == 'greater_than_or_equal_to' )selected="selected"#end>$encoder.htmlEncode( $i18n.getString( "greater_than_or_equal_to" ) )</option>
 				<option value="less_than" #if ( $validationRule.operator == 'less_than' )selected="selected"#end>$encoder.htmlEncode( $i18n.getString( "less_than" ) )</option>
 				<option value="less_than_or_equal_to" #if ( $validationRule.operator == 'less_than_or_equal_to' )selected="selected"#end>$encoder.htmlEncode( $i18n.getString( "less_than_or_equal_to" ) )</option>
+                <option value="compulsory_pair" #if ( $validationRule.operator == 'compulsory_pair' )selected="selected"#end>$encoder.htmlEncode( $i18n.getString( "compulsory_pair" ) )</option>
 			</select>
 		</td>
 	</tr>