--- a/doc/orchestration.dtd
+++ b/doc/orchestration.dtd
@@ -1,22 +1,67 @@
-<!-- DTD for the Bitten build orchestration BEEP profile. -->
+<!--
+DTD for the Bitten build orchestration BEEP profile.
+-->
 
+<!--
+Slave registration.
+-->
 <!ELEMENT register    (platform, os)>
 <!ATTLIST register
           name        CDATA             #REQUIRED
           maintainer  CDATA             #IMPLIED>
 
+<!--
+Platform/machine information for slave registration.
+-->
 <!ELEMENT platform    #PCDATA>
+<!ATTLIST os
+          processor   CDATA             #IMPLIED>
 
+<!--
+Operating system information for slave registration.
+-->
 <!ELEMENT os          #PCDATA>
 <!ATTLIST os
           family      CDATA             #REQUIRED
           version     CDATA             #IMPLIED>
 
-<!ELEMENT build       #PCDATA>
-
+<!--
+Reply message from the master when registration of a slave was successful
+-->
 <!ELEMENT ok          EMPTY>
 
+<!--
+Generic error message. Can be received in response to registration or build
+initiation.
+-->
 <!ELEMENT error       #PCDATA>
 <!ATTLIST error
           code        CDATA             #REQUIRED
           xml:lang    CDATA             #IMPLIED>
+
+<!--
+Build initiation request sent by the master to a slave.
+-->
+<!ELEMENT build       #PCDATA>
+<!ATTLIST build
+          recipe      CDATA             #REQUIRED>
+
+<!--
+Build request acknowledgement.
+-->
+<!ELEMENT started     EMPTY>
+
+<!--
+Build status reporting: ANS payload sent by the slave for every build step
+processed.
+-->
+<!ELEMENT step        #PCDATA>
+<!ATTLIST step
+          id          ID                #REQUIRED
+          result      (success|failure) #REQUIRED
+          description CDATA             #IMPLIED>
+
+<!--
+Cancellation of a build by the slave.
+-->
+<!ELEMENT aborted     #PCDATA>