rfc806.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

      3.  SEMANTICS


           This  section discusses two major topics, message processing
      functions and message field meanings.  Section 3.1 describes  the
      six  functional  groups of message fields.  The functional groups
      are Origination, Dates, Recipients,  Cross-referencing,  Message-
      handling, and Message-contents.  They are explained more fully in
      Section 3.1.1, along with detailed discussion of the semantics of
      all  the  fields in each functional group.  Section 3.2 describes
      message processing functions whose  operation  is  based  on  the
      meanings of particular message fields.



      3.1  Semantics of Message Fields


           The  definition  of  a  message  is  discussed  generally in
      Sections 1 and 2.  Semantically valid messages must  contain  one
      From  field,  one  To field, and one Posted-Date field.  They may
      contain, in addition, any number of other  fields,  depending  on
      the  processing  and  functions  supplied  by  the originating or
      receiving CBMS.  (Section  3.2  describes  classes  of  functions
      supplied by CBMSs.)


      3.1.1  Types of fields


           Message  receiving programs are required to interpret fields
      according to the semantics described in  the  remainder  of  this
      se.  The message fields defined in this document are grouped
      into the following functional categories.


        o  Originator  fields  indicate who or what participated in
           the creation of the message and where replies should  be
           directed.  (See Section 3.1.3.)

        o  Date fields record when events take place, for a variety
         events, such as message creation or expiration.  (See
           Section 3.1.5.)

        o  Recipient  fields  indicate  who  or what is intended to
           receive a message.  (See Section 3.1.4.)

        o  Cross-reference fields label a message or refer to other
           messages.  (See Section 3.1.6.)

        o  Message-handling fields record the  type  of  service  a


                                     12                          

                                                          Section 3.1.1



           message's  sender requested of a message transfer system
           or indicate how the message should  be  treated  by  its
           recipients.  (See Section 3.1.7.)

        o  Message-content   fields   either  contain  the  primary
           content of a message or index or  summarize  it.    (See
           Section 3.1.8.)

        o  Extension  fields  provide  mechanisms for extending the
           message format specification.  (See Section 3.1.9.)


      3.1.2  Semantic Compliance Categories


           For purposes of determining whether a CBMS complies with the
      semantic  requirements  of  this  message  format  specification,
      message fields have been divided into three categories:


      REQUIRED  These  fields  must be present in all messages and must
                be processed by message receiving programs  as  defined
                by the message format specification.

      BASIC     These  fields  need  not be present in all messages but
                when they do appear they must be processed  by  message
                receiving  programs  as  defined  by the message format
                specification.

      OPTIONAL  These fields need not be present in  all  messages  and
                may  be  ignored  by  message  receiving programs.  The
                exact meaning of "ignored"  is  not  specified  by  the
                message  format specification.  In general, a CBMS must
                recognize the existence of an optional field (that  is,
                optional  fields  should not cause errors) and must not
                process the field in a manner contrary to the semantics
                defined  for  that  field   by   the   message   format
                specification.


           (Syntactic compliance is defined in Section 4.1.2.)


      3.1.3  Originator fields


           A  message  originator  may  be  a person, role, or process.
      Originator fields identify a message's author, who is responsible
      for  the  message,  who  or  what  sent   it,   and   where   any
      replies should be directed.  (See Section 2.4.)



                                     13                          

                                                          Section 3.1.3



      From                     (REQUIRED)

                This  field  contains the identity of the originator(s)
                taking formal responsibility for  this  message.    The
                contents  of  the  From field is to be used for replies
                when no Reply-to field appears in a message.
      Reply-To                 (BASIC)

                This field identifies any recipients of replies to  the
                message.
      Author                   (OPTIONAL)

                This  field  identifies the individual(s) who wrote the
                primary contents of the message.   Use  of  the  Author
                  is  discouraged  when the contents of the Author
                field and the From field would be completely redundant.
      Sender                   (OPTIONAL)

                This field identifies the agent who sent  the  message.
                It is used either when the sender is not the originator
                responsible  for the message or to indicate who among a
                group  of  originators  responsible  for  the   message
                actually   sent  it.    Use  of  the  Sender  field  is
                discouraged when the contents of the Sender  field  and
                From  field  would  be  completely redundant.  Only one
                Sender field is permitted in a message.


      3.1.4  Recipient fields


           Message recipients may be people, roles, or processes.  (See
      Section 2.4).  Recipient  fields  identify  who  or  what  is  to
      receive the message.
      To                       (REQUIRED)

                This  field  identifies  the  primary  recipients  of a
                message.
      Bcc                      (OPTIONAL)

                This  field  identifies  additional  recipients  of   a
                message  (a  "blind carbon copies" list).  The contents
                of this field are not to be included in copies  of  the
                message  sent  to the primary and secondary recipients.
                See section 3.2.1 for further discussion of the use  of
                blind carbon copies lists.
      Cc                       (BASIC)

                This field identifies secondary recipients of a message
                (a "carbon copies" list).



                                     14                          

                                                          Section 3.1.4



      Circulate-Next           (OPTIONAL)

                This field is used in conjunction with the Circulate-To
                field.    (See  Section  3.2.6.1.)    It identifies all
                recipients in a circulation list who have not  received
                the message.
      Circulate-To             (OPTIONAL)

                This   field  identifies  recipients  of  a  circulated
                message.   (See  Section  3.2.6.1.)    It  is  used  in
                conjunction with the Circulate-Next field.


      3.1.5  Date fields


           Date  fields  for two kinds of uses are provided.  Dates can
      be associated with some event in the history  of  a  message  and
      dates  can  delimit  the span of time during which the message is
      meaningful (its life span).
      Posted-Date              (REQUIRED)

                This field contains the  posting  date,  which  is  the
                point  in  time  when  the  message  passes through the
                posting slot into a message transfer system.  Only  one
                Posted-Date field is permitted in a message.
      Date                     (OPTIONAL)

                This   field   contains   a  date  that  the  message's
                originator wishes to associate with  a  message.    The
                Date field is to the Posted-Date field as the date on a
                letter is to the postmark added by the post office.
      End-Date                 (OPTIONAL)

                This  field  contains the date on which a message loses
                effect.  (See also Section 3.2.5.)
      Received-Date            (OPTIONAL)

                Delivery date.  This field may be added to a message by
                the  recipient's  message  receiving   program.      It
                indicates when the message left the delivery system and
                entered the recipient's message processing domain.
      Start-Date               (OPTIONAL)

                This  field  contains the date on which a message takes
                effect.  (See also Section 3.2.5.)
      Warning-Date             (OPTIONAL)

                This field is used either alone or in conjunction  with
                an  End-Date  field.    It  contains one or more dates.
                These dates could  be  used  by  a  message  processing


                                     15                          

                                                          Section 3.1.5



                program  as  warnings of an impending end-date or other
                event.  (See also Section 3.2.5.)


      3.1.6  Cross-reference fields


           Cross reference fields can be used to identify a message and
      to provide cross references to  other  messages.    (See  Section
      3.2.4.)
      In-Reply-To              (OPTIONAL)

                This  field designates previous correspondence to which
                this message is a reply.  The usual  contents  of  this
                field  would be the contents of the Message-ID field of
                the message(s) being replied to.
      Message-ID               (OPTIONAL)

                This field contains a unique identifier for a  message.
                This  identifier is intended for machine generation and
                processing.   Further  definition  appears  in  Section
                3.2.4.1.    Only one Message-ID field is permitted in a
                message.
      Obsoletes                (OPTIONAL)

                This field identifies one or more  messages  that  this
                one supplants.
      Originator-Serial-Number (OPTIONAL)

                This field contains one or more serial numbers assigned
                by  the  message's  originator.  Messages with multiple
                recipients  should  have  the   same   value   in   the
                Originator-Serial-Number field.
      References               (OPTIONAL)

                This  field  identifies  other correspondence that this
                message  references.    If  the  other   correspondence
                contains  a  Message-ID  field,  the  contents  of  the
                References field must be the message identifier.


      3.1.7  Message-handling fields


           Message-handling fields describe aspects of how a message is
      to be handled or categorized.
      Precedence               (OPTIONAL)

                This  field  indicates  the  precedence  at  which  the
                message  was posted.  Ordinarily, message precedence or
                priority is a service request  to  a  message  transfer


                                     16                          

                                                          Section 3.1.7



                system.    A  message  originator, however, can include
                precedence information in a message.   One  example  of
                precedence  categories  are  those  used  by  the  U.S.
                Military: "ROUTINE",  "PRIORITY",  "IMMEDIATE",  "FLASH
                OVERRIDE", and "EMERGENCY COMMAND PRECEDENCE".
      Message-Class            (OPTIONAL)

                This  field  indicates  the  purpose of a message.  For
                example, it might contain values  indicating  that  the
                                                             1
                message is a memorandum or a data-base entry. 
      Reissue-Type             (OPTIONAL)

                This   field   is  used  in  conjunction  with  message
                encapsulating  (see  Section  2.4.1)  to  differentiate
                between messages being assigned or redistributed.
      Received-From            (OPTIONAL)

                This  field  contains  a  record  of  a  message's path
                through   a   message    transfer    system.        The
                recipient's  message receiving program could store here
                any information about the  transfer  that  it  obtained
                from a message transfer system.


      3.1.8  Message-content fields


           The   intent   of  most  messages  is  to  communicate  some
      particular information from originator  to  recipient.    Several
      fields in a message are designed to contain that information.
      Subject                  (BASIC)

                This  field  contains  any  information  the originator
                provided to summarize or indicate  the  nature  of  the
                message.
      Text                     (BASIC)

                This field contains the primary content of the message.
      Attachments              (OPTIONAL)

                This  field  contains  additional  data  accompanying a
                message.  It is similar in intent to  enclosures  in  a
                conventional mail system.

      _______________

        1
         The message format specification is not intended to be used as
      a  specification  for  exchanging  data-base  records.  Messages,
      however, sometimes contain data from or for a database.