FIPA ACL Message Representation
in String Specification


Document title

FIPA ACL Message Representation in String Specification

Document number


Document source

FIPA Agent Management

Document status


Date of this status





Change history


Approved for Experimental










© 2000 Foundation for Intelligent Physical Agents -

Geneva, Switzerland


Use of the technologies described in this specification may infringe patents, copyrights or other intellectual property rights of FIPA Members and non-members. Nothing in this specification should be construed as granting permission to use any of the technologies described. Anyone planning to make use of technology covered by the intellectual property rights of others should first obtain permission from the holder(s) of the rights. FIPA strongly encourages anyone implementing  any part of this specification to determine first whether part(s) sought to be implemented are covered by the intellectual property of others, and, if so, to obtain appropriate licenses or other permission from the holder(s) of such intellectual property prior to implementation. This specification is subject to change without notice. Neither FIPA nor any of its Members accept any responsibility whatsoever for damages or liability, direct or consequential, which may result from the use of this specification.


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1     Scope. 1

2     String ACL Representation. 2

2.1      Component Name. 2

2.2      Syntax. 2

2.3      Lexical Rules. 3

2.4      Representation of Time. 4

2.5      Notes on the Grammar Rules. 4

3     References. 6

1         Scope

This document is part of the FIPA specifications and deals with message transportation between inter-operating agents. This document also forms part of the FIPA Agent Management Specification [FIPA00023] and contains specifications for:


·         Syntactic representation of ACL in string form.

2         String ACL Representation

This section defines the message transport syntax for strings which is expressed in standard EBNF format (see Table 1).


Grammar rule component


Terminal tokens are enclosed in double quotes


Non-terminals are written as capitalised identifiers


Square brackets denote an optional construct

[ "," OptionalArg ]

Vertical bars denote an alternative between choices

Integer | Float

Asterisk denotes zero or more repetitions of the preceding expression


Plus denotes one or more repetitions of the preceding expression


Parentheses are used to group expansions

( A | B )*

Productions are written with the non-terminal name on the left-hand side, expansion on the right-hand side and terminated by a full stop

ANonTerminal = "terminal".


Table 1: EBNF Rules


2.1        Component Name

The name assigned to this component is:




2.2        Syntax

ACLCommunicativeAct     = Message.

Message                 = "(" MessageType

                              MessageSlot* ")".

MessageType             =
See [FIPA00037]

MessageSlot             = ":sender"

                        | ":receiver" AgentIdentifierSet

                        | ":content" String

                        | ":reply-with" Expression

                        | ":reply-by" DateTime

                        | ":in-reply-to" Expression

                        | ":reply-to" AgentIdentifierSet

                        | ":language" Expression

                        | ":encoding" Expression

                        | ":ontology" Expression

                        | ":protocol" Word

                        | ":conversation-id" Expression

                        | UserDefinedSlot Expression.

UserDefinedSlot         = Word

Expression              = Word

                        | String

                        | Number

                        | DateTime

                        | "(" Expression* ")".


AgentIdentifier         = "(" "agent-identifier"

                              ":name" word

    [ ":addresses" URLSequence ]

                            [ ":resolvers" AgentIdentifierSequence ]

                            ( UserDefinedSlot Expression )* ")".



AgentIdentifierSequence = "(" "sequence" AgentIdentifier* ")".


AgentIdentifierSet      = "(" "set" AgentIdentifier* ")".


URLSequence             = "(" "sequence" URL* ")".


DateTime                = DateTimeToken.


URL                     = See [RFC2396]


2.3        Lexical Rules

Some slightly different rules apply for the generation of lexical tokens. Lexical tokens use the same notation as above, with the exceptions noted in Table 2.


Lexical rule component


Square brackets enclose a character set

[ "a", "b", "c" ]

Dash in a character set denotes a range

[ "a” – "z" ]

Tilde denotes the complement of a character set if it is the first character

[ ~ "(", ")" ]

Post-fix question-mark operator denotes that the preceding lexical expression is optional (may appear zero or one times)

[ "0" – "9" ] ? [ "0" – "9" ]


Table 2: Lexical Rules


All white space, tabs, carriage returns and line feeds between tokens should be skipped by the lexical analyser.


Word                    = [~ "\0x00" – "\0x20", "(", ")", "#", "0" – "9", "-", "@"]

                          [~ "\0x00" – "\0x20", "(", ")"]*.


String                  = StringLiteral | ByteLengthEncodedString.


StringLiteral           = "\"" ([ ~ "\"" ] | "\\\"")* "\"".


ByteLengthEncodedString = "#" Digit+ "\"" <byte sequence>.


Number                  = Integer | Float.


URL                     = See [RFC2396]    

DateTimeToken           = "+" ?

                           Year Month Day "T"

                           Hour Minute Second MilliSecond

                           ( TypeDesignator ? ).


Year                    = Digit Digit Digit Digit.


Month                   = Digit Digit.


Day                     = Digit Digit.


Hour                    = Digit Digit.


Minute                  = Digit Digit.


Second                  = Digit Digit.


MilliSecond             = Digit Digit Digit.


TypeDesignator          = AlphaCharacter.


AlphaCharacter          = [ "a" – "z" ] | [ "A" – "Z" ].

Digit                   = [ "0" – "9" ].


Sign                    = [ "+" , "-" ] .


Integer                 = Sign? Digit+.    


Dot                     = [ "." ].


Float                   = Sign? FloatMantissa FloatExponent?

                        | Sign? Digit+ FloatExponent


FloatMantissa           = Digit+ Dot Digit*

                        | Digit* Dot Digit+


FloatExponent           = Exponent Sign? Digit+


Exponent                = [ "e", "E" ]


2.4        Representation of Time

Time tokens are based on [ISO8601], with extension for millisecond durations. If no type designator is given, the local time zone is then used. The type designator for UTC is the character Z; UTC is preferred to prevent time zone ambiguities. Note that years must be encoded in four digits. As an example, 8:30 am on 15th April, 1996 local time would be encoded as:




The same time in UTC would be:




2.5        Notes on the Grammar Rules

1.       The standard definitions for integers and floating point are assumed.


2.       All keywords are case-insensitive.


3.       A length encoded string is a context sensitive lexical token. Its meaning is as follows: the message envelope of the token is everything from the leading # to the separator " inclusive. Between the markers of the message envelope is a decimal number with at least one digit. This digit then determines that exactly that number of 8-bit bytes are to be consumed as part of the token, without restriction. It is a lexical error for less than that number of bytes to be available.


4.       Note that not all implementations of the ACC (see [FIPA00067]) will support the transparent transmission of 8-bit characters. It is the responsibility of the agent to ensure, by reference to internal API of the ACC, that a given channel is able to faithfully transmit the chosen message encoding.


5.       A well-formed message will obey the grammar, and in addition, will have at most one of each of the slots. It is an error to attempt to send a message which is not well formed. Further rules on well-formed messages may be stated or implied the operational definitions of the values of slots as these are further developed.


6.       Strings encoded in accordance with [ISO2022] may contain characters which are otherwise not permitted in the definition of Word. These characters are ESC (0x1B), SO (0x0E) and SI (0x0F). This is due to the complexity that would result from including the full [ISO2022] grammar in the above EBNF description. Hence, despite the basic description above, a word may contain any well-formed [ISO2022] encoded character, other (representations of) parentheses, spaces, or the # character. Note that parentheses may legitimately occur as part of a well formed escape sequence; the preceding restriction on characters in a word refers only to the encoded characters, not the form of the encoding.


7.       The format for time tokens is defined in section 2.4, Representation of Time.


8.       The format for an AID is defined in [FIPA00023].



3         References

[FIPA00023]      FIPA Agent Management Specification. Foundation for Intelligent Physical Agents, 2000.

[FIPA00037]      FIPA Communicative Act Library Specification. Foundation for Intelligent Physical Agents, 2000.

[FIPA00067]      FIPA Agent Message Transport Service Specification. Foundation for Intelligent Physical Agents, 2000.

[FIPA00075]      FIPA Agent Message Transport Protocol for IIOP Specification. Foundation for Intelligent Physical Agents, 2000.

[ISO2022]         Information Technology, Character Code Structure and Extension Techniques. International Standards Organisation, 1994.

[ISO8601]         Date Elements and Interchange Formats, Information Interchange-Representation of Dates and Times. International Standards Organisation, 1998.

[RFC2396]         Uniform Resource Identifiers: Generic Syntax. Request for Comments, 1998.

[1] User-defined parameters must start with ":X-".