diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/common/IntegrationEntity.java b/navalplanner-business/src/main/java/org/navalplanner/business/common/IntegrationEntity.java
index 8c070e774..87587ae11 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/common/IntegrationEntity.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/common/IntegrationEntity.java
@@ -99,7 +99,7 @@ public abstract class IntegrationEntity extends BaseEntity {
      * the private method <code>findIntegrationEntityDAO</code>, which in turn
      * calls on the abstract method <code>getIntegrationEntityDAO()</code>.
      */
-    @AssertTrue(message="code is already being used")
+    @AssertTrue(message="code is already used")
     public boolean checkConstraintUniqueCode() {
 
         /* Check if it makes sense to check the constraint .*/
@@ -166,7 +166,8 @@ public abstract class IntegrationEntity extends BaseEntity {
         IIntegrationEntityDAO<? extends IntegrationEntity>
             integrationEntityDAO = getIntegrationEntityDAO();
 
-        if (!integrationEntityDAO.getEntityClass().equals(this.getClass())) {
+        if (!integrationEntityDAO.getEntityClass().isAssignableFrom(
+            this.getClass())) {
             throw new RuntimeException(this.getClass().getName() + "::" +
                 "getIntegrationEntityDAO returns an incompatible " +
                 "DAO: " + integrationEntityDAO.getClass().getName());
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java b/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
index 79253baef..7ca8705b9 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/common/Registry.java
@@ -24,6 +24,7 @@ import org.navalplanner.business.advance.daos.IAdvanceTypeDAO;
 import org.navalplanner.business.calendars.daos.IBaseCalendarDAO;
 import org.navalplanner.business.common.daos.IConfigurationDAO;
 import org.navalplanner.business.costcategories.daos.ICostCategoryDAO;
+import org.navalplanner.business.costcategories.daos.IResourcesCostCategoryAssignmentDAO;
 import org.navalplanner.business.costcategories.daos.ITypeOfWorkHoursDAO;
 import org.navalplanner.business.externalcompanies.daos.IExternalCompanyDAO;
 import org.navalplanner.business.labels.daos.ILabelDAO;
@@ -35,8 +36,10 @@ import org.navalplanner.business.orders.daos.IOrderDAO;
 import org.navalplanner.business.orders.daos.IOrderElementDAO;
 import org.navalplanner.business.qualityforms.daos.IQualityFormDAO;
 import org.navalplanner.business.resources.daos.ICriterionDAO;
+import org.navalplanner.business.resources.daos.ICriterionSatisfactionDAO;
 import org.navalplanner.business.resources.daos.ICriterionTypeDAO;
 import org.navalplanner.business.resources.daos.IMachineDAO;
+import org.navalplanner.business.resources.daos.IResourceDAO;
 import org.navalplanner.business.resources.daos.IWorkerDAO;
 import org.navalplanner.business.users.daos.IProfileDAO;
 import org.navalplanner.business.users.daos.IUserDAO;
@@ -132,6 +135,16 @@ public class Registry {
     @Autowired
     private IWorkReportDAO workReportDAO;
 
+    @Autowired
+    private IResourceDAO resourceDAO;
+
+    @Autowired
+    private ICriterionSatisfactionDAO criterionSatisfactionDAO;
+
+    @Autowired
+    private IResourcesCostCategoryAssignmentDAO
+        resourcesCostCategoryAssignmentDAO;
+
     private Registry() {
     }
 
@@ -230,4 +243,19 @@ public class Registry {
         return getInstance().workReportDAO;
     }
 
+    public static IResourceDAO getResourceDAO() {
+        return getInstance().resourceDAO;
+    }
+
+    public static ICriterionSatisfactionDAO getCriterionSatisfactionDAO() {
+        return getInstance().criterionSatisfactionDAO;
+    }
+
+    public static IResourcesCostCategoryAssignmentDAO
+        getResourcesCostCategoryAssignmentDAO() {
+
+        return getInstance().resourcesCostCategoryAssignmentDAO;
+
+    }
+
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/IResourcesCostCategoryAssignmentDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/IResourcesCostCategoryAssignmentDAO.java
index ffd351b4a..c73b8e43f 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/IResourcesCostCategoryAssignmentDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/IResourcesCostCategoryAssignmentDAO.java
@@ -20,12 +20,13 @@
 
 package org.navalplanner.business.costcategories.daos;
 
-import org.navalplanner.business.common.daos.IGenericDAO;
+import org.navalplanner.business.common.daos.IIntegrationEntityDAO;
 import org.navalplanner.business.costcategories.entities.ResourcesCostCategoryAssignment;
 
 /**
  * @author Jacobo Aragunde Perez <jaragunde@igalia.com>
  */
-public interface IResourcesCostCategoryAssignmentDAO extends IGenericDAO<ResourcesCostCategoryAssignment, Long> {
+public interface IResourcesCostCategoryAssignmentDAO
+    extends IIntegrationEntityDAO<ResourcesCostCategoryAssignment> {
 
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ResourcesCostCategoryAssignmentDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ResourcesCostCategoryAssignmentDAO.java
index 9cc02ddf9..326b11805 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ResourcesCostCategoryAssignmentDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/daos/ResourcesCostCategoryAssignmentDAO.java
@@ -20,7 +20,7 @@
 
 package org.navalplanner.business.costcategories.daos;
 
-import org.navalplanner.business.common.daos.GenericDAOHibernate;
+import org.navalplanner.business.common.daos.IntegrationEntityDAO;
 import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
 import org.navalplanner.business.costcategories.entities.ResourcesCostCategoryAssignment;
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -32,9 +32,9 @@ import org.springframework.stereotype.Repository;
  */
 @Repository
 @Scope(BeanDefinition.SCOPE_SINGLETON)
-public class ResourcesCostCategoryAssignmentDAO extends
-        GenericDAOHibernate<ResourcesCostCategoryAssignment, Long> implements
-        IResourcesCostCategoryAssignmentDAO {
+public class ResourcesCostCategoryAssignmentDAO
+    extends IntegrationEntityDAO<ResourcesCostCategoryAssignment>
+    implements IResourcesCostCategoryAssignmentDAO {
 
     @Override
     public void remove(Long id) throws InstanceNotFoundException {
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/ResourcesCostCategoryAssignment.java b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/ResourcesCostCategoryAssignment.java
index 342e747fe..334ef67c2 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/ResourcesCostCategoryAssignment.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/costcategories/entities/ResourcesCostCategoryAssignment.java
@@ -26,17 +26,18 @@ import org.apache.commons.lang.StringUtils;
 import org.hibernate.validator.AssertTrue;
 import org.hibernate.validator.NotNull;
 import org.joda.time.LocalDate;
-import org.navalplanner.business.common.BaseEntity;
+import org.navalplanner.business.common.IntegrationEntity;
 import org.navalplanner.business.common.Registry;
 import org.navalplanner.business.common.exceptions.CreateUnvalidatedException;
 import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
+import org.navalplanner.business.costcategories.daos.IResourcesCostCategoryAssignmentDAO;
 import org.navalplanner.business.resources.entities.Resource;
 
 /**
  * @author Jacobo Aragunde Perez <jaragunde@igalia.com>
  * @author Fernando Bellas Permuy <fbellas@udc.es>
  */
-public class ResourcesCostCategoryAssignment extends BaseEntity {
+public class ResourcesCostCategoryAssignment extends IntegrationEntity {
 
     private LocalDate initDate;
 
@@ -56,8 +57,9 @@ public class ResourcesCostCategoryAssignment extends BaseEntity {
     }
 
     public static ResourcesCostCategoryAssignment createUnvalidated(
-        String costCategoryName, Resource resource, LocalDate initDate,
-        LocalDate endDate) throws CreateUnvalidatedException {
+        String code, String costCategoryName, Resource resource,
+        LocalDate initDate, LocalDate endDate)
+        throws CreateUnvalidatedException {
 
         /* Get CostCategory. */
         if (StringUtils.isBlank(costCategoryName)) {
@@ -76,7 +78,7 @@ public class ResourcesCostCategoryAssignment extends BaseEntity {
 
         /* Create instance of ResourcesCostCategoryAssignment. */
         ResourcesCostCategoryAssignment assignment =
-            create(new ResourcesCostCategoryAssignment());
+            create(new ResourcesCostCategoryAssignment(), code);
 
         assignment.initDate = initDate;
         assignment.endDate = endDate;
@@ -150,4 +152,9 @@ public class ResourcesCostCategoryAssignment extends BaseEntity {
         return initDate != null;
     }
 
+    @Override
+    protected IResourcesCostCategoryAssignmentDAO getIntegrationEntityDAO() {
+        return Registry.getResourcesCostCategoryAssignmentDAO();
+    }
+
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/CriterionSatisfactionDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/CriterionSatisfactionDAO.java
index 309e09f0f..67b386d8c 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/CriterionSatisfactionDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/CriterionSatisfactionDAO.java
@@ -20,7 +20,7 @@
 
 package org.navalplanner.business.resources.daos;
 
-import org.navalplanner.business.common.daos.GenericDAOHibernate;
+import org.navalplanner.business.common.daos.IntegrationEntityDAO;
 import org.navalplanner.business.resources.entities.CriterionSatisfaction;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.context.annotation.Scope;
@@ -33,7 +33,7 @@ import org.springframework.stereotype.Repository;
  */
 @Repository
 @Scope(BeanDefinition.SCOPE_SINGLETON)
-public class CriterionSatisfactionDAO extends
-        GenericDAOHibernate<CriterionSatisfaction, Long> implements
-        ICriterionSatisfactionDAO {
+public class CriterionSatisfactionDAO
+    extends IntegrationEntityDAO<CriterionSatisfaction>
+    implements ICriterionSatisfactionDAO {
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ICriterionSatisfactionDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ICriterionSatisfactionDAO.java
index 1bef1ddf9..ee01e3320 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ICriterionSatisfactionDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ICriterionSatisfactionDAO.java
@@ -20,14 +20,14 @@
 
 package org.navalplanner.business.resources.daos;
 
-import org.navalplanner.business.common.daos.IGenericDAO;
+import org.navalplanner.business.common.daos.IIntegrationEntityDAO;
 import org.navalplanner.business.resources.entities.CriterionSatisfaction;
 
 /**
  * DAO for {@link CriterionSatisfaction} <br />
  * @author Óscar González Fernández <ogonzalez@igalia.com>
  */
-public interface ICriterionSatisfactionDAO extends
-        IGenericDAO<CriterionSatisfaction, Long> {
+public interface ICriterionSatisfactionDAO
+    extends IIntegrationEntityDAO<CriterionSatisfaction> {
 
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/IResourceDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/IResourceDAO.java
index e7df3a938..79821a6d6 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/IResourceDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/IResourceDAO.java
@@ -23,7 +23,7 @@ package org.navalplanner.business.resources.daos;
 import java.util.Collection;
 import java.util.List;
 
-import org.navalplanner.business.common.daos.IGenericDAO;
+import org.navalplanner.business.common.daos.IIntegrationEntityDAO;
 import org.navalplanner.business.planner.entities.Task;
 import org.navalplanner.business.resources.entities.Criterion;
 import org.navalplanner.business.resources.entities.Machine;
@@ -36,7 +36,7 @@ import org.navalplanner.business.resources.entities.Worker;
  * @author Fernando Bellas Permuy <fbellas@udc.es>
  * @author Diego Pino Garcia <dpino@igalia.com>
  */
-public interface IResourceDAO extends IGenericDAO<Resource, Long> {
+public interface IResourceDAO extends IIntegrationEntityDAO<Resource> {
 
     public List<Worker> getWorkers();
 
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ResourceDAO.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ResourceDAO.java
index 08aa08c70..46d4f7704 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ResourceDAO.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/daos/ResourceDAO.java
@@ -29,7 +29,7 @@ import java.util.Set;
 
 import org.apache.commons.lang.Validate;
 import org.hibernate.Query;
-import org.navalplanner.business.common.daos.GenericDAOHibernate;
+import org.navalplanner.business.common.daos.IntegrationEntityDAO;
 import org.navalplanner.business.planner.entities.Task;
 import org.navalplanner.business.resources.entities.Criterion;
 import org.navalplanner.business.resources.entities.Machine;
@@ -48,8 +48,8 @@ import org.springframework.transaction.annotation.Transactional;
 @Repository
 @Scope(BeanDefinition.SCOPE_SINGLETON)
 @Transactional
-public class ResourceDAO extends GenericDAOHibernate<Resource, Long> implements
-        IResourceDAO {
+public class ResourceDAO extends IntegrationEntityDAO<Resource> implements
+    IResourceDAO {
 
     @Override
     public List<Worker> getWorkers() {
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/CriterionSatisfaction.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/CriterionSatisfaction.java
index 5bade1167..6381764e4 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/CriterionSatisfaction.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/CriterionSatisfaction.java
@@ -30,17 +30,18 @@ import org.apache.commons.lang.Validate;
 import org.apache.commons.lang.builder.ToStringBuilder;
 import org.hibernate.validator.AssertTrue;
 import org.hibernate.validator.NotNull;
-import org.navalplanner.business.common.BaseEntity;
+import org.navalplanner.business.common.IntegrationEntity;
 import org.navalplanner.business.common.Registry;
 import org.navalplanner.business.common.exceptions.CreateUnvalidatedException;
 import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
+import org.navalplanner.business.resources.daos.ICriterionSatisfactionDAO;
 import org.navalplanner.business.resources.daos.ICriterionTypeDAO;
 /**
  * Declares a interval of time in which the criterion is satisfied <br />
  * @author Óscar González Fernández <ogonzalez@igalia.com>
  * @author Fernando Bellas Permuy <fbellas@udc.es>
  */
-public class CriterionSatisfaction extends BaseEntity {
+public class CriterionSatisfaction extends IntegrationEntity {
 
     public static final Comparator<CriterionSatisfaction> BY_START_COMPARATOR;
 
@@ -56,28 +57,26 @@ public class CriterionSatisfaction extends BaseEntity {
     }
 
     public static CriterionSatisfaction create() {
-        CriterionSatisfaction criterionSatisfaction = new CriterionSatisfaction();
-        criterionSatisfaction.setNewObject(true);
-        return criterionSatisfaction;
+        return create(new CriterionSatisfaction());
     }
 
     public static CriterionSatisfaction create(Date startDate,
             Criterion criterion, Resource resource) {
-        CriterionSatisfaction criterionSatisfaction = new CriterionSatisfaction(
-                startDate, criterion, resource);
-        criterionSatisfaction.setNewObject(true);
-        return criterionSatisfaction;
+
+        return create(
+            new CriterionSatisfaction(startDate, criterion, resource));
+
     }
 
     public static CriterionSatisfaction create(Criterion criterion,
             Resource resource, Interval interval) {
-        CriterionSatisfaction criterionSatisfaction = new CriterionSatisfaction(criterion, resource, interval);
-        criterionSatisfaction.setNewObject(true);
-        return criterionSatisfaction;
+
+        return create(new CriterionSatisfaction(criterion, resource, interval));
+
     }
 
     public static CriterionSatisfaction createUnvalidated(
-        String criterionTypeName, String criterionName,
+        String code, String criterionTypeName, String criterionName,
         Resource resource, Date startDate, Date finishDate)
         throws CreateUnvalidatedException {
 
@@ -117,7 +116,7 @@ public class CriterionSatisfaction extends BaseEntity {
 
         /* Create instance of CriterionSatisfaction. */
         CriterionSatisfaction criterionSatisfaction =
-            create(new CriterionSatisfaction());
+            create(new CriterionSatisfaction(), code);
 
         criterionSatisfaction.criterion = criterion;
         criterionSatisfaction.resource = resource;
@@ -301,4 +300,9 @@ public class CriterionSatisfaction extends BaseEntity {
         return startDate != null;
     }
 
+    @Override
+    protected ICriterionSatisfactionDAO getIntegrationEntityDAO() {
+        return Registry.getCriterionSatisfactionDAO();
+    }
+
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Machine.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Machine.java
index e543352b5..7509154c0 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Machine.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Machine.java
@@ -25,13 +25,8 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
-import org.apache.commons.lang.StringUtils;
-import org.hibernate.validator.AssertTrue;
 import org.hibernate.validator.NotEmpty;
 import org.hibernate.validator.Valid;
-import org.navalplanner.business.common.Registry;
-import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
-import org.navalplanner.business.resources.daos.IMachineDAO;
 
 /**
 * Entity
@@ -41,8 +36,6 @@ import org.navalplanner.business.resources.daos.IMachineDAO;
 */
 public class Machine extends Resource {
 
-    private String code;
-
     private String name;
 
     private String description;
@@ -67,9 +60,8 @@ public class Machine extends Resource {
     public static Machine createUnvalidated(String code, String name,
         String description) {
 
-        Machine machine = create(new Machine());
+        Machine machine = create(new Machine(), code);
 
-        machine.code = code;
         machine.name = name;
         machine.description = description;
 
@@ -77,29 +69,17 @@ public class Machine extends Resource {
 
     }
 
+    /**
+     * Used by Hibernate. Do not use!
+     */
     protected Machine() {
 
     }
 
-    protected Machine(String code, String name, String description) {
-        this.code = code;
-        this.name = name;
-        this.description = description;
-    }
-
     public static Machine create() {
         return create(new Machine());
     }
 
-    @NotEmpty(message="machine code not specified")
-    public String getCode() {
-        return code;
-    }
-
-    public void setCode(String code) {
-        this.code = code;
-    }
-
     @NotEmpty(message="machine name not specified")
     public String getName() {
         return name;
@@ -114,7 +94,7 @@ public class Machine extends Resource {
     }
 
     public String getShortDescription() {
-        return code + " :: " + name;
+        return getCode() + " :: " + name;
     }
 
     public void setDescription(String description) {
@@ -127,45 +107,6 @@ public class Machine extends Resource {
         return compositedCriterion.isSatisfiedBy(this);
     }
 
-    @AssertTrue(message="machine code has to be unique. It is already used")
-    public boolean checkConstraintUniqueCode() {
-
-        /* Check if it makes sense to check the constraint .*/
-        if (!isCodeSpecified()) {
-            return true;
-        }
-
-        /* Check the constraint. */
-        boolean result;
-        if (isNewObject()) {
-            result = !existsMachineWithTheCode();
-        } else {
-            result = isIfExistsTheExistentMachineThisOne();
-        }
-        return result;
-
-    }
-
-    private boolean isCodeSpecified() {
-        return !StringUtils.isBlank(code);
-    }
-
-    private boolean existsMachineWithTheCode() {
-        IMachineDAO machineDAO = Registry.getMachineDAO();
-        return machineDAO.existsMachineWithCodeInAnotherTransaction(code);
-    }
-
-    private boolean isIfExistsTheExistentMachineThisOne() {
-        IMachineDAO machineDAO = Registry.getMachineDAO();
-        try {
-            Machine machine =
-                machineDAO.findUniqueByCodeInAnotherTransaction(code);
-            return machine.getId().equals(getId());
-        } catch (InstanceNotFoundException e) {
-            return true;
-        }
-    }
-
     @Override
     protected boolean isCriterionSatisfactionOfCorrectType(
        CriterionSatisfaction c) {
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Resource.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Resource.java
index e9b03d990..1b55943d1 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Resource.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Resource.java
@@ -43,13 +43,14 @@ import org.navalplanner.business.calendars.entities.BaseCalendar;
 import org.navalplanner.business.calendars.entities.IWorkHours;
 import org.navalplanner.business.calendars.entities.ResourceCalendar;
 import org.navalplanner.business.calendars.entities.SameWorkHoursEveryDay;
-import org.navalplanner.business.common.BaseEntity;
+import org.navalplanner.business.common.IntegrationEntity;
 import org.navalplanner.business.common.Registry;
 import org.navalplanner.business.common.exceptions.InstanceNotFoundException;
 import org.navalplanner.business.common.exceptions.MultipleInstancesException;
 import org.navalplanner.business.common.exceptions.ValidationException;
 import org.navalplanner.business.costcategories.entities.ResourcesCostCategoryAssignment;
 import org.navalplanner.business.planner.entities.DayAssignment;
+import org.navalplanner.business.resources.daos.IResourceDAO;
 
 /**
  * This class acts as the base class for all resources.
@@ -57,7 +58,7 @@ import org.navalplanner.business.planner.entities.DayAssignment;
  * @author Susana Montes Pedreira <smontes@wirelessgalicia.com>
  * @author Jacobo Aragunde Perez <jaragunde@igalia.com>
  */
-public abstract class Resource extends BaseEntity{
+public abstract class Resource extends IntegrationEntity {
 
     public static List<Machine> machines(
             Collection<? extends Resource> resources) {
@@ -941,6 +942,18 @@ public abstract class Resource extends BaseEntity{
 
     }
 
+    @AssertTrue(message="criterion satisfaction codes must be unique inside " +
+        "a resource")
+    public boolean checkConstraintNonRepeatedCriterionSatisfactionCodes() {
+        return getFirstRepeatedCode(criterionSatisfactions) == null;
+    }
+
+    @AssertTrue(message="resources cost category assignment codes must be " +
+        "unique inside a resource")
+    public boolean checkConstraintNonRepeatedResourcesCostCategoryAssignmentCodes() {
+        return getFirstRepeatedCode(resourcesCostCategoryAssignments) == null;
+    }
+
     protected boolean isCriterionSatisfactionOfCorrectType(
         CriterionSatisfaction c) {
 
@@ -948,4 +961,8 @@ public abstract class Resource extends BaseEntity{
 
     }
 
+    protected IResourceDAO getIntegrationEntityDAO() {
+        return Registry.getResourceDAO();
+    }
+
 }
diff --git a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Worker.java b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Worker.java
index 4b6d0545e..b5103ef92 100644
--- a/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Worker.java
+++ b/navalplanner-business/src/main/java/org/navalplanner/business/resources/entities/Worker.java
@@ -36,21 +36,20 @@ import org.navalplanner.business.common.Registry;
 public class Worker extends Resource {
 
     public static Worker create() {
-        Worker worker = new Worker();
-        worker.setNewObject(true);
-        return worker;
+        return create(new Worker());
     }
 
-    public static Worker create(String firstName, String surname, String nif) {
-        Worker worker = new Worker(firstName, surname, nif);
-        worker.setNewObject(true);
-        return worker;
-    }
-
-    public static Worker createUnvalidated(String firstName, String surname,
+    public static Worker create(String firstName, String surname,
         String nif) {
 
-        Worker worker = create(new Worker());
+        return create(new Worker(firstName, surname, nif));
+
+    }
+
+    public static Worker createUnvalidated(String code, String firstName,
+        String surname, String nif) {
+
+        Worker worker = create(new Worker(), code);
 
         worker.firstName = firstName;
         worker.surname = surname;
diff --git a/navalplanner-business/src/main/resources/org/navalplanner/business/costcategories/entities/CostCategories.hbm.xml b/navalplanner-business/src/main/resources/org/navalplanner/business/costcategories/entities/CostCategories.hbm.xml
index a9b29706d..abde01e03 100644
--- a/navalplanner-business/src/main/resources/org/navalplanner/business/costcategories/entities/CostCategories.hbm.xml
+++ b/navalplanner-business/src/main/resources/org/navalplanner/business/costcategories/entities/CostCategories.hbm.xml
@@ -70,6 +70,8 @@
     </id>
     <version name="version" access="property" type="long" />
 
+    <property name="code" access="property" not-null="true" unique="true"/>
+
     <property name="initDate" type="org.joda.time.contrib.hibernate.PersistentLocalDate"/>
 
     <property name="endDate" type="org.joda.time.contrib.hibernate.PersistentLocalDate"/>
diff --git a/navalplanner-business/src/main/resources/org/navalplanner/business/resources/entities/Resources.hbm.xml b/navalplanner-business/src/main/resources/org/navalplanner/business/resources/entities/Resources.hbm.xml
index cdabb89b8..e560a00ec 100644
--- a/navalplanner-business/src/main/resources/org/navalplanner/business/resources/entities/Resources.hbm.xml
+++ b/navalplanner-business/src/main/resources/org/navalplanner/business/resources/entities/Resources.hbm.xml
@@ -12,6 +12,7 @@
             Hibernate infers type="integer".
         -->
     <version name="version" access="property" type="long" />
+    <property name="code" access="property" not-null="true" unique="true"/>
     <set access="field" cascade="all-delete-orphan" inverse="true" name="criterionSatisfactions">
       <key column="resource" not-null="true"/>
       <one-to-many class="CriterionSatisfaction"/>
@@ -46,7 +47,6 @@
 
     <joined-subclass name="org.navalplanner.business.resources.entities.Machine">
       <key column="MACHINE_ID"/>
-      <property name="code"/>
       <property name="name"/>
       <property name="description"/>
       <set inverse="true" name="configurationUnits" cascade="all-delete-orphan">
@@ -98,6 +98,7 @@
       </generator>
     </id>
     <version name="version" access="property" type="long" />
+    <property name="code" access="property" not-null="true" unique="true"/>
     <property access="field" name="startDate" not-null="true"/>
     <property access="field" name="finishDate"/>
     <property access="field" name="isDeleted"/>
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/CriterionSatisfactionDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/CriterionSatisfactionDTO.java
index 748099fdc..1924bfde1 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/CriterionSatisfactionDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/CriterionSatisfactionDTO.java
@@ -24,12 +24,16 @@ import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlSchemaType;
 import javax.xml.datatype.XMLGregorianCalendar;
 
+import org.navalplanner.ws.common.api.IntegrationEntityDTO;
+
 /**
  * DTO for <code>CriterionSatisfaction</code> entity.
  *
  * @author Fernando Bellas Permuy <fbellas@udc.es>
  */
-public class CriterionSatisfactionDTO {
+public class CriterionSatisfactionDTO extends IntegrationEntityDTO {
+
+    public final static String ENTITY_TYPE = "criterion-satisfaction";
 
     @XmlAttribute(name="criterion-type-name")
     public String criterionTypeName;
@@ -47,10 +51,11 @@ public class CriterionSatisfactionDTO {
 
     public CriterionSatisfactionDTO() {}
 
-    public CriterionSatisfactionDTO(
+    public CriterionSatisfactionDTO(String code,
         String criterionTypeName, String criterionName,
         XMLGregorianCalendar startDate, XMLGregorianCalendar endDate) {
 
+        super(code);
         this.criterionTypeName = criterionTypeName;
         this.criterionName = criterionName;
         this.startDate = startDate;
@@ -58,4 +63,23 @@ public class CriterionSatisfactionDTO {
 
     }
 
+    /**
+     * This constructor automatically generates a unique code. It is intended
+     * to facilitate the implementation of test cases that add new instances
+     * (such instances will have a unique code).
+     */
+    public CriterionSatisfactionDTO(
+        String criterionTypeName, String criterionName,
+        XMLGregorianCalendar startDate, XMLGregorianCalendar endDate) {
+
+        this(generateCode(), criterionTypeName, criterionName, startDate,
+            endDate);
+
+    }
+
+    @Override
+    public String getEntityType() {
+        return ENTITY_TYPE;
+    }
+
 }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/MachineDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/MachineDTO.java
index 246a3477c..23f97238c 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/MachineDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/MachineDTO.java
@@ -29,8 +29,7 @@ import javax.xml.bind.annotation.XmlAttribute;
  */
 public class MachineDTO extends ResourceDTO {
 
-    @XmlAttribute
-    public String code;
+    public final static String ENTITY_TYPE = "machine";
 
     @XmlAttribute
     public String name;
@@ -41,9 +40,23 @@ public class MachineDTO extends ResourceDTO {
     public MachineDTO() {}
 
     public MachineDTO(String code, String name, String description) {
-        this.code = code;
+        super(code);
         this.name = name;
         this.description = description;
     }
 
+    /**
+     * This constructor automatically generates a unique code. It is intended
+     * to facilitate the implementation of test cases that add new instances
+     * (such instances will have a unique code).
+     */
+    public MachineDTO(String name, String description) {
+        this(generateCode(), name, description);
+    }
+
+    @Override
+    public String getEntityType() {
+        return ENTITY_TYPE;
+    }
+
 }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourceDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourceDTO.java
index e1ba48f83..a7ba4656d 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourceDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourceDTO.java
@@ -27,12 +27,14 @@ import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlElementWrapper;
 
+import org.navalplanner.ws.common.api.IntegrationEntityDTO;
+
 /**
  * DTO for <code>Resource</code> entity.
  *
  * @author Fernando Bellas Permuy <fbellas@udc.es>
  */
-public abstract class ResourceDTO {
+public abstract class ResourceDTO extends IntegrationEntityDTO {
 
     @XmlAttribute(name="calendar-name")
     public String calendarName;
@@ -48,4 +50,10 @@ public abstract class ResourceDTO {
         resourcesCostCategoryAssignments =
             new ArrayList<ResourcesCostCategoryAssignmentDTO>();
 
+    protected ResourceDTO() {}
+
+    protected ResourceDTO(String code) {
+        super(code);
+    }
+
 }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourcesCostCategoryAssignmentDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourcesCostCategoryAssignmentDTO.java
index b3004e7ea..a40eb2141 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourcesCostCategoryAssignmentDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/ResourcesCostCategoryAssignmentDTO.java
@@ -23,12 +23,17 @@ import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlSchemaType;
 import javax.xml.datatype.XMLGregorianCalendar;
 
+import org.navalplanner.ws.common.api.IntegrationEntityDTO;
+
 /**
  * DTO for <code>ResourcesCostCategoryAssignment</code> entity.
  *
  * @author Fernando Bellas Permuy <fbellas@udc.es>
  */
-public class ResourcesCostCategoryAssignmentDTO {
+public class ResourcesCostCategoryAssignmentDTO extends IntegrationEntityDTO {
+
+     public final static String ENTITY_TYPE =
+         "resources-cost-category-assignment";
 
     @XmlAttribute(name="cost-category-name")
     public String costCategoryName;
@@ -43,13 +48,33 @@ public class ResourcesCostCategoryAssignmentDTO {
 
     public ResourcesCostCategoryAssignmentDTO() {}
 
-    public ResourcesCostCategoryAssignmentDTO(String costCategoryName,
-        XMLGregorianCalendar startDate, XMLGregorianCalendar endDate) {
+    public ResourcesCostCategoryAssignmentDTO(String code,
+        String costCategoryName, XMLGregorianCalendar startDate,
+        XMLGregorianCalendar endDate) {
 
+        super(code);
         this.costCategoryName = costCategoryName;
         this.startDate = startDate;
         this.endDate = endDate;
 
     }
 
+    /**
+     * This constructor automatically generates a unique code. It is intended
+     * to facilitate the implementation of test cases that add new instances
+     * (such instances will have a unique code).
+     */
+    public ResourcesCostCategoryAssignmentDTO(
+        String costCategoryName, XMLGregorianCalendar startDate,
+        XMLGregorianCalendar endDate) {
+
+        this(generateCode(), costCategoryName, startDate, endDate);
+
+    }
+
+    @Override
+    public String getEntityType() {
+        return ENTITY_TYPE;
+    }
+
 }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/WorkerDTO.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/WorkerDTO.java
index 5aea49125..cdeb73eb1 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/WorkerDTO.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/api/WorkerDTO.java
@@ -29,6 +29,8 @@ import javax.xml.bind.annotation.XmlAttribute;
  */
 public class WorkerDTO extends ResourceDTO {
 
+    public final static String ENTITY_TYPE = "worker";
+
     @XmlAttribute(name="first-name")
     public String firstName;
 
@@ -40,10 +42,28 @@ public class WorkerDTO extends ResourceDTO {
 
     public WorkerDTO() {}
 
-    public WorkerDTO(String firstName, String surname, String nif) {
+    public WorkerDTO(String code, String firstName, String surname,
+        String nif) {
+
+        super(code);
         this.firstName = firstName;
         this.surname = surname;
         this.nif = nif;
+
+    }
+
+    /**
+     * This constructor automatically generates a unique code. It is intended
+     * to facilitate the implementation of test cases that add new instances
+     * (such instances will have a unique code).
+     */
+    public WorkerDTO(String firstName, String surname, String nif) {
+        this(generateCode(), firstName, surname, nif);
+    }
+
+    @Override
+    public String getEntityType() {
+        return ENTITY_TYPE;
     }
 
 }
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceConverter.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceConverter.java
index 4da3d47c4..a255570ea 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceConverter.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceConverter.java
@@ -76,16 +76,23 @@ public class ResourceConverter {
 
     private final static Machine createResourceWithBasicData(
         MachineDTO machineDTO) {
-        return Machine.createUnvalidated(StringUtils.trim(machineDTO.code),
+
+        return Machine.createUnvalidated
+            (StringUtils.trim(machineDTO.code),
             StringUtils.trim(machineDTO.name),
             StringUtils.trim(machineDTO.description));
+
     }
 
     private final static Worker createResourceWithBasicData(
         WorkerDTO workerDTO) {
-        return Worker.createUnvalidated(StringUtils.trim(workerDTO.firstName),
+
+        return Worker.createUnvalidated(
+            StringUtils.trim(workerDTO.code),
+            StringUtils.trim(workerDTO.firstName),
             StringUtils.trim(workerDTO.surname),
             StringUtils.trim(workerDTO.nif));
+
     }
 
     private static void addCriterionSatisfactions(Resource resource,
@@ -109,6 +116,7 @@ public class ResourceConverter {
         throws CreateUnvalidatedException {
 
         return CriterionSatisfaction.createUnvalidated(
+            StringUtils.trim(criterionSatisfactionDTO.code),
             StringUtils.trim(criterionSatisfactionDTO.criterionTypeName),
             StringUtils.trim(criterionSatisfactionDTO.criterionName),
             resource,
@@ -154,7 +162,7 @@ public class ResourceConverter {
         throws CreateUnvalidatedException {
 
         return ResourcesCostCategoryAssignment.createUnvalidated(
-            assignmentDTO.costCategoryName, resource,
+            assignmentDTO.code, assignmentDTO.costCategoryName, resource,
             DateConverter.toLocalDate(assignmentDTO.startDate),
             DateConverter.toLocalDate(assignmentDTO.endDate));
 
diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceServiceREST.java b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceServiceREST.java
index fcaadb28f..c7609cfa7 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceServiceREST.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/ws/resources/impl/ResourceServiceREST.java
@@ -88,8 +88,8 @@ public class ResourceServiceREST implements IResourceService {
             } catch (CreateUnvalidatedException e) {
                 instanceConstraintViolationsDTO =
                     InstanceConstraintViolationsDTO.create(
-                        Util.generateInstanceId(instanceNumber,
-                            getUserProvidedId(resourceDTO)),
+                        Util.generateInstanceConstraintViolationsDTOId(
+                            (long) instanceNumber, resourceDTO),
                         e.getMessage());
             }
 
@@ -102,10 +102,10 @@ public class ResourceServiceREST implements IResourceService {
 
                         instanceConstraintViolationsDTO =
                             InstanceConstraintViolationsDTO.create(
-                                Util.generateInstanceId(instanceNumber,
-                                    getUserProvidedId(resourceDTO)),
-                                    getDuplicatedImportedResourceErrorMessage(
-                                        resourceDTO));
+                                Util.generateInstanceConstraintViolationsDTOId(
+                                    (long) instanceNumber, resourceDTO),
+                                getDuplicatedImportedResourceErrorMessage(
+                                    resourceDTO));
 
                     } else {
 
@@ -125,9 +125,8 @@ public class ResourceServiceREST implements IResourceService {
                 } catch (ValidationException e) {
                     instanceConstraintViolationsDTO =
                         ConstraintViolationConverter.toDTO(
-                            Util.generateInstanceId(instanceNumber,
-                                getUserProvidedId(resourceDTO)),
-                            e.getInvalidValues());
+                            Util.generateInstanceConstraintViolationsDTOId(
+                                (long) instanceNumber, resourceDTO), e);
                 }
             }
 
diff --git a/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/common/Util.java b/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/common/Util.java
index 0934aaefd..2922c349f 100644
--- a/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/common/Util.java
+++ b/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/common/Util.java
@@ -20,6 +20,7 @@
 
 package org.navalplanner.web.test.ws.common;
 
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 import java.util.List;
@@ -66,6 +67,8 @@ public class Util {
         InstanceConstraintViolationsListDTO
         instanceConstraintViolationsListDTO) {
 
+        assertNotNull(instanceConstraintViolationsListDTO.
+            instanceConstraintViolationsList);
         assertTrue(
             instanceConstraintViolationsListDTO.
             instanceConstraintViolationsList.toString(),
@@ -82,9 +85,13 @@ public class Util {
             instanceConstraintViolationsListDTO.
                 instanceConstraintViolationsList;
 
+        assertNotNull(instanceConstraintViolationsListDTO.
+            instanceConstraintViolationsList);
         assertTrue(
             instanceConstraintViolationsList.toString(),
             instanceConstraintViolationsList.size() == 1);
+        assertNotNull(instanceConstraintViolationsList.get(0).
+            constraintViolations);
         assertTrue(
             instanceConstraintViolationsList.get(0).
             constraintViolations.toString(),
@@ -101,12 +108,14 @@ public class Util {
             instanceConstraintViolationsListDTO.
                 instanceConstraintViolationsList;
 
+         assertNotNull(instanceConstraintViolationsList);
          assertTrue(
              instanceConstraintViolationsList.toString(),
              instanceConstraintViolationsList.size() == numberOfInstances);
 
          for (InstanceConstraintViolationsDTO i :
              instanceConstraintViolationsList) {
+             assertNotNull(i.constraintViolations);
              assertTrue(
                  i.constraintViolations.toString(),
                  i.constraintViolations.size() == 1);
diff --git a/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/resources/api/ResourceServiceTest.java b/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/resources/api/ResourceServiceTest.java
index 45fed1158..709796b85 100644
--- a/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/resources/api/ResourceServiceTest.java
+++ b/navalplanner-webapp/src/test/java/org/navalplanner/web/test/ws/resources/api/ResourceServiceTest.java
@@ -193,7 +193,8 @@ public class ResourceServiceTest {
     public void testAddWorkerWithExistingFirstNameSurnameAndNif() {
 
         /* Create a worker. */
-        Worker w1 = Worker.createUnvalidated(getUniqueName(), "surname", "nif");
+        Worker w1 = Worker.createUnvalidated(getUniqueName(), getUniqueName(),
+            "surname", "nif");
         saveResource(w1);
 
         /*
diff --git a/scripts/rest-clients/resources-sample-mini.xml b/scripts/rest-clients/resources-sample-mini.xml
index a07fd00d4..3c17bdb59 100644
--- a/scripts/rest-clients/resources-sample-mini.xml
+++ b/scripts/rest-clients/resources-sample-mini.xml
@@ -7,6 +7,7 @@
     <machine code="machineA" name="name" description="desc">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="machineA-s1"
                 criterion-type-name="LOCATION_GROUP"
                 criterion-name="TestLocationGroupCriterion"
                 start-date="2009-01-01"
@@ -14,9 +15,11 @@
         </criterion-satisfaction-list>
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="machineA-a1"
                 cost-category-name="TestCostCategory"
                 start-date="2001-01-01"/>
             <resources-cost-category-assignment
+                code="machineA-a2"
                 cost-category-name="TestCostCategory"
                 start-date="2000-01-01"
                 end-date="2000-04-01"/>
@@ -24,15 +27,17 @@
     </machine>
 
     <!-- [It assumes existence of "TestCalendar" and "TestCostCategory"] OK -->
-    <worker first-name="workerA" surname="surname" nif="nif"
+    <worker code="workerA" first-name="workerA" surname="surname" nif="nif"
         calendar-name="TestCalendar">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="workerA-s1"
                 criterion-type-name="WORK_RELATIONSHIP"
                 criterion-name="hiredResourceWorkingRelationship"
                 start-date="2009-01-01"
                 end-date=""/>
             <criterion-satisfaction
+                code="workerA-s2"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2009-12-24"
@@ -40,9 +45,11 @@
         </criterion-satisfaction-list>
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="workerA-a1"
                 cost-category-name="TestCostCategory"
                 start-date="2001-01-01"/>
             <resources-cost-category-assignment
+                code="workerA-a2"
                 cost-category-name="TestCostCategory"
                 start-date="2000-01-01"
                 end-date="2000-04-01"/>
diff --git a/scripts/rest-clients/resources-sample.xml b/scripts/rest-clients/resources-sample.xml
index 61f691e97..ef71f7cd7 100644
--- a/scripts/rest-clients/resources-sample.xml
+++ b/scripts/rest-clients/resources-sample.xml
@@ -12,13 +12,11 @@
     <!-- OK -->
     <machine code="m1" name="m1-name" description="m1-desc"/>
 
-    <!--  Missing code and name (description is optional). -->
-    <machine code="" description=""/>
-
     <!--  Criterion satisfaction of incorrect type. -->
     <machine code="m2" name="m2-name" description="m2-desc">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="m2-a1"
                 criterion-type-name="WORK_RELATIONSHIP"
                 criterion-name="hiredResourceWorkingRelationship"
                 start-date="2009-01-01"
@@ -37,9 +35,11 @@
     <machine code="m5" name="m5-name" description="m5-desc">
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="m5-a1"
                 cost-category-name="TestCostCategory"
                 start-date="2001-01-01"/>
             <resources-cost-category-assignment
+                code="m5-a2"
                 cost-category-name="TestCostCategory"
                 start-date="2000-01-01"
                 end-date="2000-04-01"/>
@@ -50,6 +50,7 @@
     <machine code="m6" name="m6-name" description="m6-desc">
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="m6-a1"
                 cost-category-name="TestCostCategory"
                 end-date="2000-01-01"/>
         </resources-cost-category-assignment-list>
@@ -59,6 +60,7 @@
     <machine code="m7" name="m7-name" description="m7-desc">
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="m7-a1"
                 cost-category-name="TestCostCategory"
                 start-date="2000-02-01"
                 end-date="2000-01-01"/>
@@ -69,27 +71,34 @@
     <machine code="m8" name="m8-name" description="m8-desc">
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="m8-a1"
                 cost-category-name="TestCostCategory"
                 start-date="2000-02-01"
                 end-date="2000-05-01"/>
             <resources-cost-category-assignment
+                code="m8-a2"
                 cost-category-name="TestCostCategory"
                 start-date="2000-01-01"
                 end-date="2000-03-01"/>
         </resources-cost-category-assignment-list>
     </machine>
 
+    <!--  Missing code and name (description is optional). -->
+    <machine code="" description=""/>
+
     <!--  *** Workers *** -->
 
     <!-- OK -->
-    <worker first-name="w1-firstName" surname="w1-surname" nif="w1-nif">
+    <worker code="w1" first-name="w1-firstName" surname="w1-surname" nif="w1-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w1-s1"
                 criterion-type-name="WORK_RELATIONSHIP"
                 criterion-name="hiredResourceWorkingRelationship"
                 start-date="2009-01-01"
                 end-date=""/>
             <criterion-satisfaction
+                code="w1-s2"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2009-12-24"
@@ -97,13 +106,11 @@
         </criterion-satisfaction-list>
     </worker>
 
-    <!--  Missing first name, surname, and nif. -->
-    <worker first-name="" nif=""/>
-
     <!--  Missing start date in criterion satisfaction. -->
-    <worker first-name="w2-firstName" surname="w2-surname" nif="w2-nif">
+    <worker code="w2" first-name="w2-firstName" surname="w2-surname" nif="w2-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w2-s1"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 end-date="2009-12-25"/>
@@ -111,9 +118,10 @@
     </worker>
 
     <!--  Non-existent criterion type. -->
-    <worker first-name="w3-firstName" surname="w3-surname" nif="w3-nif">
+    <worker code="w3" first-name="w3-firstName" surname="w3-surname" nif="w3-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w3-s1"
                 criterion-type-name="WORK_RELATIONSHIP_XXX"
                 criterion-name="hiredResourceWorkingRelationship"
                 start-date="2009-01-01"
@@ -122,9 +130,10 @@
     </worker>
 
     <!--  Non-existent criterion. -->
-    <worker first-name="w4-firstName" surname="w4-surname" nif="w4-nif">
+    <worker code="w4" first-name="w4-firstName" surname="w4-surname" nif="w4-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w4-s1"
                 criterion-type-name="WORK_RELATIONSHIP"
                 criterion-name="hiredResourceWorkingRelationshipXXX"
                 start-date="2009-01-01"
@@ -133,9 +142,10 @@
     </worker>
 
     <!-- Criterion not specified. -->
-    <worker first-name="w5-firstName" surname="w5-surname" nif="w5-nif">
+    <worker code="w5" first-name="w5-firstName" surname="w5-surname" nif="w5-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w5-s1"
                 criterion-type-name="WORK_RELATIONSHIP"
                 start-date="2009-01-01"
                 end-date=""/>
@@ -143,33 +153,35 @@
     </worker>
 
     <!-- Criterion type not specified. -->
-    <worker first-name="w6-firstName" surname="w6-surname" nif="w6-nif">
+    <worker code="w6" first-name="w6-firstName" surname="w6-surname" nif="w6-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w6-s1"
                 criterion-name="hiredResourceWorkingRelationship"
                 start-date="2009-01-01"
                 end-date=""/>
         </criterion-satisfaction-list>
     </worker>
 
-    <!-- Another worker is being imported with the same first name, surname,
-         and nif. -->
-    <worker first-name="w1-firstName" surname="w1-surname" nif="w1-nif"/>
+    <!--  Missing first name, surname, and nif. -->
+    <worker code="w7" first-name="" nif=""/>
 
     <!-- OK or not OK depending on the existence of "TestCalendar". -->
-    <worker first-name="w8-firstName" surname="w8-surname" nif="w8-nif"
+    <worker code="w8" first-name="w8-firstName" surname="w8-surname" nif="w8-nif"
         calendar-name="TestCalendar" />
 
     <!-- [It assumes existence of "TestCalendar" and "TestCostCategory"] OK -->
-    <worker first-name="w9-firstName" surname="w9-surname" nif="w9-nif"
+    <worker code="w9" first-name="w9-firstName" surname="w9-surname" nif="w9-nif"
         calendar-name="TestCalendar">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w9-s1"
                 criterion-type-name="WORK_RELATIONSHIP"
                 criterion-name="hiredResourceWorkingRelationship"
                 start-date="2009-01-01"
                 end-date=""/>
             <criterion-satisfaction
+                code="w9-s2"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2009-12-24"
@@ -177,9 +189,11 @@
         </criterion-satisfaction-list>
         <resources-cost-category-assignment-list>
             <resources-cost-category-assignment
+                code="w9-a1"
                 cost-category-name="TestCostCategory"
                 start-date="2001-01-01"/>
             <resources-cost-category-assignment
+                code="w9-a2"
                 cost-category-name="TestCostCategory"
                 start-date="2000-01-01"
                 end-date="2000-04-01"/>
@@ -187,9 +201,10 @@
     </worker>
 
     <!--  Negative interval. -->
-    <worker first-name="w10-firstName" surname="w10-surname" nif="w10-nif">
+    <worker code="w10" first-name="w10-firstName" surname="w10-surname" nif="w10-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w10-s1"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2000-02-01"
@@ -198,14 +213,16 @@
     </worker>
 
     <!-- Criterion satisfaction overlapping in "LEAVE :: paternityLeave". -->
-    <worker first-name="w11-firstName" surname="w11-surname" nif="w11-nif">
+    <worker code="w11" first-name="w11-firstName" surname="w11-surname" nif="w11-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w11-s1"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2000-01-01"
                 end-date="2000-02-01"/>
             <criterion-satisfaction
+                code="w11-s2"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2000-01-15"
@@ -215,14 +232,16 @@
 
     <!-- Criterion satisfaction overlapping (LEAVE does not allow
          simultaneous criterion satisfactions in intervals that overlap). -->
-    <worker first-name="w12-firstName" surname="w12-surname" nif="w12-nif">
+    <worker code="w12" first-name="w12-firstName" surname="w12-surname" nif="w12-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w12-s1"
                 criterion-type-name="LEAVE"
                 criterion-name="paternityLeave"
                 start-date="2000-01-01"
                 end-date="2000-02-01"/>
             <criterion-satisfaction
+                code="w12-s2"
                 criterion-type-name="LEAVE"
                 criterion-name="medicalLeave"
                 start-date="2000-01-15"
@@ -234,14 +253,16 @@
          "TestLocationGroupCriterion2"] OK
          (LOCATION_GROUP allows simultaneous criterion satisfactions in
          intervals that overlap). -->
-    <worker first-name="w13-firstName" surname="w13-surname" nif="w13-nif">
+    <worker code="w13" first-name="w13-firstName" surname="w13-surname" nif="w13-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w13-s1"
                 criterion-type-name="LOCATION_GROUP"
                 criterion-name="TestLocationGroupCriterion"
                 start-date="2000-01-01"
                 end-date="2000-02-01"/>
             <criterion-satisfaction
+                code="w13-s2"
                 criterion-type-name="LOCATION_GROUP"
                 criterion-name="TestLocationGroupCriterion2"
                 start-date="2000-01-15"
@@ -252,14 +273,16 @@
     <!-- [It assumes existence of "TestLocationGroupCriterion" and
          "TestLocationGroupCriterion2"] Criterion satisfaction overlapping in
          "LOCATION_GROUP :: TestLocationGroupCriterion". -->
-    <worker first-name="w14-firstName" surname="w14-surname" nif="w14-nif">
+    <worker code="w14" first-name="w14-firstName" surname="w14-surname" nif="w14-nif">
         <criterion-satisfaction-list>
             <criterion-satisfaction
+                code="w14-s1"
                 criterion-type-name="LOCATION_GROUP"
                 criterion-name="TestLocationGroupCriterion"
                 start-date="2000-01-01"
                 end-date="2000-02-01"/>
             <criterion-satisfaction
+                code="w14-s2"
                 criterion-type-name="LOCATION_GROUP"
                 criterion-name="TestLocationGroupCriterion"
                 start-date="2000-01-15"
@@ -267,4 +290,8 @@
         </criterion-satisfaction-list>
     </worker>
 
+    <!-- Another worker is being imported with the same first name, surname,
+         and nif. -->
+    <worker code="w15" first-name="w1-firstName" surname="w1-surname" nif="w1-nif"/>
+
 </resource-list>