--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/prevayler/Command.java	Sat Mar 21 11:00:06 2009 +0000
@@ -0,0 +1,53 @@
+/*
+  The copyright of all source code included in this Prevayler distribution is
+  held by Klaus Wuestefeld, except the files that specifically state otherwise.
+  All rights are reserved. "PREVAYLER" is a trademark of Klaus Wuestefeld.
+
+
+  BSD License:
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+  - Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+  - Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+ 
+  - Neither the name of Prevayler nor the names of its contributors may be used
+  to endorse or promote products derived from this software without specific
+  prior written permission.
+
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
+  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
+  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
+  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+  POSSIBILITY OF SUCH DAMAGE.
+*/
+
+package org.prevayler;
+
+import java.io.Serializable;
+
+
+/**
+ * An atomic transaction to be executed on a PrevalentSystem. Any operation which changes the observable state of a PrevalentSystem must be encapsulated as a Command.
+ */
+public interface Command extends Serializable {
+
+  /**
+   * Executes this command on the received system. See org.prevayler.demos for examples. The returned object has to be Serializable in preparation for future versions of Prevayler that will provide fault-tolerance through system replicas.
+   * @return The object returned by the execution of this command. Most commands simply return null.
+   */
+  public Serializable execute(PrevalentSystem system) throws Exception;
+
+}