CASA Messages

CASA messages are pure-text messages used by agents to communicate with one another. CASA mesages are represented in the software by the class MLMessage. Currently, CASA supports either XML or KQML formats for messages (see classes XMLMessage and KQMLMessage).

The following table summarizes the CASA message fields:

required.
Type: token. The token must occur in the casa ontology as a sub-type of performative.

The perfomatives form a type lattice as follows. For an updated and complete list, refer to dataFiles/actions.ont.lisp in the CASA files.

Thus, a request is an inform, and a reply is both an inform and an ack (acknowledge). Furthermore, nothing can be both a request and a reply.

In addition, a request is always followed by a reply (unless something goes wrong of course).

In reliable channel mode, we further declare that every inform is to be acknowledged. The type lattice above tells use that both requests and replies (and all their subtypes) must be followed by an ack (in the reverse direction), but that a reply to a request suffices as an ack.

Further subtypes supplementing the above lattice are:

Example:

:performative request

required
Type: token (see below)

Example:

:act joinCD

required
Type: URL

Example:

:sender casa://kremer@192.168.1.42:2000/casa/Agent/Agent3#lac=8700

required
Type: { URL }+

• If there are several URLs in the receiver field, strip the first one (the URL of this agent) off and forward the message to the next URL in the list.
• If there is only one URL in reciever:
• If there is a to field, and it's different from the URL of this agent, then forward the message to the URL in the to field.
• If there is no to field, or the to field contains the URL of this agent, then the message is intended for this agent, so process it normally.

Example:

:receiver casa://192.168.1.42:9000 casa://kremer@192.168.1.42:7602/casa/TransientAgent/agent7601-temp#lac=9000#indirect=true

optional
Type: URL

Specifies the ultimate destination of the message. An agent recieving a message with a to field that is not not a reference to itself is normally expected to forward the message to the agent specified in the two field. Some agents may modify this behaviour, however. For example, security agents may block a message from being forwarded, or mediateor agents may route a message to a different agent perhaps to balance the load on service agents.

If the to field is empty or missing, the message shall normally be interpreted as being identical to the receiver field. However, agents may modify this behaviour. For example, a Cooperation Domain may forward a message with a blank or missing to field to each of it's members.

Example:

:to casa://kremer@192.168.1.42:7602/casa/TransientAgent/agent7601-temp#lac=9000

required if |performative| <: request
Type: string

Example:

:reply-with kremer@192.168.1.42:7601/casa/Agent/agent7601--1

required if |performative| <: reply
Type: string

Example:

:in-reply-to kremer@192.168.1.42:7601/casa/Agent/agent7601--1

optional
Type: any

Example:

( :request
  :act resolve-url
  :sender casa://kremer@192.168.1.42:7602/casa/TransientAgent/agent7601-temp
  :receiver casa://kremer@192.168.1.42:8700#lac=8700
  :content casa://kremer@192.168.1.42/casa/Agent/agent7600#lac=8700
  :language casa.URLdescriptor
  :language-version 1.0
  :reply-with casa://kremer@192.168.1.42:7601/casa/Agent/agent7601--1
)

required if content is not empty

Example:

( :request
  :act resolve-url
  :sender casa://kremer@192.168.1.42:7602/casa/TransientAgent/agent7601-temp
  :receiver casa://kremer@192.168.1.42:8700#lac=8700
  :content casa://kremer@192.168.1.42/casa/Agent/agent7600#lac=8700
  :language casa.URLdescriptor
  :language-version 1.0
  :reply-with casa://kremer@192.168.1.42:7601/casa/Agent/agent7601--1
)

required if languate is not empty
digit+{.{digit}+}*

Example:

:language-version 1.0

optional

Example:

:ontology manufactoring4

required if ontology is not empty
digit+{.{digit}+}*

Example:

:ontology-version 1.6.24

optional
Type: long

Example:

:timeout 1056804965073

optional
Type: string - protocol name

• the initiator of the protocol must assign a non-null value to the conversation-id parameter,
  
• all responses to the message, within the scope of the same interaction protocol, should contain the same value for the conversation-id parameter, and,
  
• the timeout value in the reply-by parameter must denote the latest time by which the sending agent would like to have received the next message in the protocol flow (not be confused with the latest time by which the interaction protocol should terminate).

Example:

:protocol request

optional
Type: string

Example:

:conversation-id casa://kremer@10.0.1.6:8700/casa/CooperationDomain/coolness?lac=9000--22

optional
Type:int

Example:

:priority -5

optional

Example:

optional

Example:

optional

Example:

optional

Example:

optional

Example:

optional

Example:

optional

Example:

optional

Example:

optional

Example:

optional
Type: {past|[present|future} The tense of the act. This is a semantic qualifier (Saeed 1997). It can be used to supplement a message with additional semantic information.

Example:

optional
Type: {perfect|imperfect|progressive}

Example:

optional
Type: long

Example:

optional

Example:

Saeed, John I. (1997). Semantics. Blackwell Publishers Ltd., Oxford, UK. ISBN 0-631-20035.