The second step of the method describes the conversation model of the MAS.
The agent communication language is a subset of KQML [14].
The conversation model is defined by choosing, for each service,
the sequence of messages (conversation), as well as their performative
and the content of each message.
Some conversations may start in the middle of other conversations. For example,
imagine agent a,
requested for a service by agent b, that has to require an accessory
service to agent c, in order to reply to agent b.
A relation sc defines which conversations
eventually start during other conversations. Let 
be
a conversation composed by messages 
and let 
be another
conversation. 
denotes that must start after message
in 
has been handled by the receiving agent.
denotes that
eventually starts after message has been handled by the
receiving agent.
In the latter case, the decision about starting is up to the receiving
agent.