Communicative Action Notation
Actions| Yielders| Data
Communicative action notation is primarily concerned with specifying the processing of permanent information (communications).
Actions
send Y |
remove Y |
offer Y |
patiently Y
- All primitive communicative actions:
- Give no transients.
- Produce no bindings.
- Make no changes to storage.
- Redirect no bindings.
- Give no transients.
- There is only a unary communicative action combinator.
- send Y: a primitive communicative action, where Y yields a sort of message.
Represents initiating the transmission of a message. The usual form of Y is
a message [to Y1] [containing Y2], where
Y1 and Y2 yield individuals.
- Indivisible. Commits and completes when the sort of message
yielded by Y includes a message from the current performer (with
the next serial number). Fails otherwise.
- Emits a message of the sort yielded by Y. The serial
number of the message is the successor of that of the previous message
sent (or contract offered) by the performing agent. Message
transmission is reliable, but each message takes an implementation-dependent
'time' to arrive (so message transmission between two
particular agents is not necessarily order-preserving).
- remove Y: a primitive communicative action, where Y is a yielder of individual messages. Represents that a particular message in the buffer has been processed and is to be discarded.
- Indivisible. Commits and completes when the message yielded by
Y is in the buffer. Fails otherwise.
- Removes the message yielded by Y from the buffer.
- offer Y: a primitive communicative action, where Y yields sort of contract. Represents initiating the arrangement of a contract with another, perhaps only partially specified, agent. The usual form of Y is a contract [to an agent] [containing abstraction of A], where A is the action to be performed according to the contract.
- Indivisible. Commits and completes when the sort of contract
yielded by Y includes an individual contract from the performer.
Fails otherwise.
- Gives no data.
- Requests the arrangement of a contract of the sort yielded by
Y. Offered contracts are distinguished by serial numbers, as
with sent messages. The arrangement of a contract takes an
implementation-dependent 'time', which must be finite when there is
a continually uncontracted agent of the specified sort.
- patiently A: a communicative action, where A is an action. Represents busy waiting while A fails. Only useful when A refers to information that may change due to some other action, for instance, the messages in the buffer.
- Performs A indivisibly, but not indivisible itself. If the
performance fails it tries again. Thus it diverges when A always fails.
- Functionally as A.
- Declaratively as A.
Actions | Yielders | Data
- Indivisible. Commits and completes when the sort of message
yielded by Y includes a message from the current performer (with
the next serial number). Fails otherwise.
Yielders
current buffer | performing-agent | contracting-agent
- current buffer: a yielder of buffers. Yields the list of
messages that have appeared in the buffer, but which have not yet been
removed. The messages are listed in the order of their arrival in the
buffer.
- performing-agent: a yielder of agents. Yields (the identity of) the agent that is performing the enclosing action.
- contracting-agent: a yielder of agents. Yields (the identity of) the agent that offered the contract to the performer.
Actions | Yielders | Data
- performing-agent: a yielder of agents. Yields (the identity of) the agent that is performing the enclosing action.
Data
agent |
user agent |
buffer |
communication |
message |
sendable |
contract |
contents d |
sender |
receiver |
serial
- agent: a sort of datum. An agent identifies a potential
process of performing an action, representing a piece of
distributed processing. It is loosely-specified, as the
maximum number and distribution of processes is usually implementation-dependent.
Each agent has its own buffer and storage. It is inactive until it accepts a contract to perform an action, whereafter it remains active for ever, even after the termination of the contracted action.
- user-agent: a distinguished agent. It corresponds to the environment of a program, providing input and accepting output. The user agent is initially the only agent with a contract.
- buffer: a sort of datum. A buffer is a list of messages sent to the same agent, in the order of their arrival.
- communication: a sort of datum. Individual communications represent information that can be transmitted by agents. Communications have components indicating their sender, receiver, and contents. Moreover, each communication is distinguished by a serial number determined by the sender.
- message: a subsort of communication. Messages can be sent directly from one agent to another.
- sendable: a sort of data. The data that can be the contents of messages sent between agents. Left open, as it depends on the variety of permanent information processed by the programs of a programming language. (Specified to include abstraction and agent to allow proper use of subordinate Y.)
- contract: a subsort of communication. Contracts can be offered by one agent to another (sort of) agent. The contents of a contract is the abstraction to be enacted by an agent accepting the contract.
- contents d : data, where d is a communication. The data contained in d .
- sender d : a datum, where d is a communication. The agent that sends d .
- receiver d : a datum, where d is a communication. The agent that receives d .
- serial d : a datum, where d is a communication. The serial number of d , determined locally when it is emitted.
- d [containing d 1]: a subsort of communication, where d 1 is a (sort of) data, and d is a sort of communication. It includes only those communications in d whose contents is (of sort) d1.
- d [from d 1]: a subsort of communication, where d 1 is a (sort of) agent, and d is a sort of communication. It includes only those communications in d whose sender is (of sort) d1.
- d [to d 1]: a subsort of communication, where d 1 is a (sort of) agent, and d is a sort of communication. It includes only those communications in d whose receiver is (of sort) d 1.
- d [at d 1]: a subsort of communication, where d 1 is a (sort of) natural number, and d is a sort of communication. It includes only those communications in d whose serial number is (of sort) d 1.
Actions | Yielders | Data
- user-agent: a distinguished agent. It corresponds to the environment of a program, providing input and accepting output. The user agent is initially the only agent with a contract.
[Created by Jin Jin Yi and Ana Carla Santos. Last modified at 21 Dec 1997 by Ana Carla]