Index: Core/Common/src/Core.Common.Base/Service/Activity.cs
===================================================================
diff -u -r3b28759abc544be3c226b517080a032b3b9d1401 -reeb8bcc69eda031ff6363caf83e8893e2abe9a04
--- Core/Common/src/Core.Common.Base/Service/Activity.cs	(.../Activity.cs)	(revision 3b28759abc544be3c226b517080a032b3b9d1401)
+++ Core/Common/src/Core.Common.Base/Service/Activity.cs	(.../Activity.cs)	(revision eeb8bcc69eda031ff6363caf83e8893e2abe9a04)
@@ -1,34 +1,44 @@
 using System;
+using System.Collections.Generic;
 using Core.Common.Base.Properties;
 using log4net;
 
 namespace Core.Common.Base.Service
 {
     /// <summary>
-    /// Defines basic activity which can be executed as part of the workflow.
+    /// Abstract class that can be used for performing activies (like calculations, data imports, data exports, etc.).
+    /// The regular workflow for completely performing an <see cref="Activity"/> is: <see cref="Execute"/> -> <see cref="Finish"/>.
+    /// <see cref="Cancel"/> can be called for cancelling a running <see cref="Activity"/>.
     /// </summary>
-    /// <example>
-    /// <para>Regular workflow for an activity is: Initialize -> Execute -> Finish -> Cleanup.</para>
-    /// <para>Regular workflow for an activity with an error occurring: [Initialize/Execute/Finish] -> ! Exception / Error ! -> Cleanup.</para> 
-    /// <para>Regular workflow for an activity being cancelled: [Initialize/Execute/Finish] -> ! Cancel ! -> Cleanup.</para>
-    /// </example>
     public abstract class Activity
     {
         public event EventHandler ProgressChanged;
+
         private readonly ILog log = LogManager.GetLogger(typeof(Activity));
         private string progressText;
 
+        /// <summary>
+        /// Constructs a new <see cref="Activity"/>.
+        /// </summary>
         protected Activity()
         {
-            Log = "";
+            LogMessages = new List<string>();
         }
 
-        public string Log { get; set; }
-
+        /// <summary>
+        /// Gets or sets the name of the <see cref="Activity"/>.
+        /// </summary>
         public virtual string Name { get; set; }
 
+        /// <summary>
+        /// Gets or sets the <see cref="ActivityStatus"/> of the <see cref="Activity"/>.
+        /// </summary>
         public ActivityStatus Status { get; protected set; }
 
+        /// <summary>
+        /// Gets or sets the progress text of the <see cref="Activity"/>.
+        /// <see cref="ProgressChanged"/> listeners are notified when the progress text is set.
+        /// </summary>
         public string ProgressText
         {
             get
@@ -43,41 +53,50 @@
             }
         }
 
+        /// <summary>
+        /// Gets or sets the collection of log messages of the <see cref="Activity"/> (which is appended while performing the <see cref="Activity"/>).
+        /// </summary>
+        public IList<string> LogMessages { get; private set; }
+
+        /// <summary>
+        /// This method runs the <see cref="Activity"/> by sequentially making calls to <see cref="Initialize"/> and <see cref="Execute"/>.
+        /// </summary>
         public void Run()
         {
-            try
+            Initialize();
+
+            if (Status == ActivityStatus.Failed)
             {
-                Initialize();
+                log.ErrorFormat(Resources.Activity_Run_Initialization_of_0_has_failed, Name);
+                return;
+            }
 
-                if (Status == ActivityStatus.Failed)
-                {
-                    throw new Exception(string.Format(Resources.Activity_Run_Initialization_of_0_has_failed, Name));
-                }
+            if (Status == ActivityStatus.Cancelled)
+            {
+                log.WarnFormat(Resources.Activity_Run_Execution_of_0_has_been_canceled, Name);
+                return;
+            }
 
-                if (Status == ActivityStatus.Cancelled)
-                {
-                    log.WarnFormat(Resources.Activity_Run_Execution_of_0_has_been_canceled, Name);
-                    return;
-                }
+            Execute();
 
-                Execute();
-
-                if (Status == ActivityStatus.Failed)
-                {
-                    throw new Exception(string.Format(Resources.Activity_Run_Execution_of_0_has_failed, Name));
-                }
-            }
-            catch (Exception exception)
+            if (Status == ActivityStatus.Failed)
             {
-                log.Error(exception.Message);
+                log.ErrorFormat(Resources.Activity_Run_Execution_of_0_has_failed, Name);
             }
         }
 
+        /// <summary>
+        /// This method cancels a running <see cref="Activity"/>.
+        /// </summary>
         public void Cancel()
         {
             ChangeState(OnCancel, ActivityStatus.Cancelling, ActivityStatus.Cancelled);
         }
 
+        /// <summary>
+        /// This method finishes an <see cref="Activity"/> that successfully ran.
+        /// Successfully ran activities can be identified by a <see cref="Status"/> not equal to <see cref="ActivityStatus.Failed"/> or <see cref="ActivityStatus.Cancelled"/>.
+        /// </summary>
         public void Finish()
         {
             if (Status != ActivityStatus.Failed && Status != ActivityStatus.Cancelled)
@@ -86,11 +105,18 @@
             }
         }
 
+        /// <summary>
+        /// This method initializes an <see cref="Activity"/>.
+        /// </summary>
         protected void Initialize()
         {
             ChangeState(OnInitialize, ActivityStatus.Initializing, ActivityStatus.Initialized);
         }
 
+        /// <summary>
+        /// This method executes an <see cref="Activity"/> that successfully initialized.
+        /// Successfully ran activities can be identified by a <see cref="Status"/> not equal to <see cref="ActivityStatus.Failed"/> or <see cref="ActivityStatus.Cancelled"/>.
+        /// </summary>
         protected void Execute()
         {
             if (Status == ActivityStatus.Finished || Status == ActivityStatus.Cancelled || Status == ActivityStatus.Failed || Status == ActivityStatus.None)
@@ -126,14 +152,6 @@
             Status = ActivityStatus.Executed;
         }
 
-        private void OnProgressChanged()
-        {
-            if (ProgressChanged != null)
-            {
-                ProgressChanged(this, EventArgs.Empty);
-            }
-        }
-
         /// <summary>
         /// Initializes internal state to prepare for execution. After calling this method,
         /// <see cref="Status"/> will be set to <see cref="ActivityStatus.Initialized"/> if
@@ -166,6 +184,14 @@
         /// </summary>
         protected abstract void OnCancel();
 
+        private void OnProgressChanged()
+        {
+            if (ProgressChanged != null)
+            {
+                ProgressChanged(this, EventArgs.Empty);
+            }
+        }
+
         private void ChangeState(Action transitionAction, ActivityStatus statusBefore, ActivityStatus statusAfter)
         {
             try
Index: Core/Common/src/Core.Common.Gui/Forms/ProgressDialog/ActivityProgressDialog.cs
===================================================================
diff -u -r45c065296e76b454bcef8ae508bc39954ff813e1 -reeb8bcc69eda031ff6363caf83e8893e2abe9a04
--- Core/Common/src/Core.Common.Gui/Forms/ProgressDialog/ActivityProgressDialog.cs	(.../ActivityProgressDialog.cs)	(revision 45c065296e76b454bcef8ae508bc39954ff813e1)
+++ Core/Common/src/Core.Common.Gui/Forms/ProgressDialog/ActivityProgressDialog.cs	(.../ActivityProgressDialog.cs)	(revision eeb8bcc69eda031ff6363caf83e8893e2abe9a04)
@@ -59,7 +59,7 @@
                     {
                         if (RunReportLogAppender.Instance != null)
                         {
-                            RunReportLogAppender.Instance.AppendMessageLineAction = message => runningActivity.Log += message;
+                            RunReportLogAppender.Instance.AppendMessageLineAction = message => runningActivity.LogMessages.Add(message);
                         }
 
                         runningActivity.ProgressChanged += ActivityOnProgressChanged;
Index: Ringtoets/Piping/src/Ringtoets.Piping.Service/PipingCalculationActivity.cs
===================================================================
diff -u -r1f79b34c12554e2b9878f6296168d18232cc9852 -reeb8bcc69eda031ff6363caf83e8893e2abe9a04
--- Ringtoets/Piping/src/Ringtoets.Piping.Service/PipingCalculationActivity.cs	(.../PipingCalculationActivity.cs)	(revision 1f79b34c12554e2b9878f6296168d18232cc9852)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Service/PipingCalculationActivity.cs	(.../PipingCalculationActivity.cs)	(revision eeb8bcc69eda031ff6363caf83e8893e2abe9a04)
@@ -35,6 +35,7 @@
             }
             else
             {
+                LogMessages.Clear();
                 calculation.Output = null;
             }
         }