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rfc:rfc138

Network Working Group Bob Anderson Request for Comments: 138 Rand NIC 6715 Vint Cerf

                                                                  UCLA
                                                          Eric Harslem
                                                          John Heafner
                                                                  Rand
                                                            Jim Madden
                                                        U. of Illinois
                                                          Bob Metcalfe
                                                                   MIT
                                                         Arie Shoshani
                                                                   SDC
                                                             Jim White
                                                                  UCSB
                                                            David Wood
                                                                 Mitre
                                                         28 April 1971
       STATUS REPORT ON PROPOSED DATA RECONFIGURATION SERVICE
                               CONTENTS
   I.  INTRODUCTION .................................    2
       Purpose of this RFC ..........................    2
       Motivation ...................................    2
  II.  OVERVIEW OF DATA RECONFIGURATION SERVICE .....    3
       Elements of Data Reconfiguration Service .....    3
       Conceptual Network Connections ...............    3
       Connection Protocols and Message Formats .....    4
       Example Connection Configurations ............    6
 III.  THE FORM MACHINE .............................    7
       Input/Output Stream and Forms ................    7
       Form Machine BNF Syntax ......................    7
       Alternate Specification of Form Machine Syntax    8
       Forms ........................................    9
       Rules ........................................   10
       Terms ........................................   10
         Term Format 1 ..............................   11
         Term Format 2 ..............................   11
         Term Format 3 ..............................   13
         Term Format 4 ..............................   13
         Application of a Term ......................   14

Anderson, et al. [Page 1] RFC 138 Data Reconfiguration Service April 1971

         Restrictions and Interpretations of
           Term Functions ...........................   14
       Term and Rule Sequencing .....................   16
  IV.  EXAMPLES .....................................   16
       Remarks ......................................   16
       Field Insertion ..............................   17
       Deletion .....................................   17
       Variable Length Records ......................   17
       String Length Computation ....................   18
       Transposition ................................   18
       Character Packing and Unpacking ..............   18
   V.  PROPOSED USES OF DATA RECONFIGURATION SERVICE    19
  VI.  IMPLEMENTATION PLANS .........................   20
 Appendix A .........................................   21
       Note 1 to the DRS Working Group ..............   21
       Note 2 to the DRS Working Group ..............   22

I. INTRODUCTION

 PURPOSE OF THIS RFC
 The purpose of this RFC is to describe, in part, a proposed Network
 experiment and to solicit comments on any aspect of the experiment.
 The experiment involves a software mechanism to reformat Network data
 streams.  The mechanism can be adapted to numerous Network
 application programs.  We hope that the results of the experiment
 will lead to a further standard service that embodies the principles
 described in this RFC.   We would like comments on the
 appropriateness of this work as a Network experiment and also
 comments on particular Network data reformatting needs that could not
 easily be accomplished using these techniques.

MOTIVATION

 Application programs require specific data I/O formats yet the
 formats are different from program to program.  We take the position
 that the Network should adapt to the individual program requirements
 rather than changing each program to comply with a standard.  This
 position doesn't preclude the use of standards that describe the
 formats of regular message contents; it is merely an interpretation
 of a standard as being a desirable mode of operation but not a
 necessary one.

Anderson, et al. [Page 2] RFC 138 Data Reconfiguration Service April 1971

 In addition to differing program requirements, a format mismatch
 problem occurs where users wish to employ many different kinds of
 consoles to attach to a single service program.  It is desirable to
 have the Network adapt to individual console configurations rather
 than requiring unique software packages for each console
 transformation.
 One approach to providing adaptation is for those sites with
 substantial computing power to offer a data reconfiguration service;
 a proposed example of such a service is described here.
 The envisioned modus operandi of the service is that an applications
 programmer defines _forms_ that describe data reconfigurations.  The
 service stores the forms by name.  At a later time, a user (perhaps a
 non-programmer) employs the service to accomplish a particular
 transformation of a Network data stream, simply by calling the form
 by name.
 We have attempted to provide a notation tailored to some specifically
 needed instances of data reformatting while keeping the notation and
 its underlying implementation within some utility range that is
 bounded on the lower end by a notation expressive enough to make the
 experimental service useful, and that is bounded on the upper end by
 a notation short of a general purpose programming language.

II. OVERVIEW OF THE DATA RECONFIGURATION SERVICE

ELEMENTS OF THE DATA RECONFIGURATION SERVICE

 An implementation of the Data Reconfiguration Service (DRS) includes
 modules for connection protocols, a handler of some requests that can
 be made of the service, a compiler and/or interpreter (called the
 Form Machine) to act on those requests, and a file storage module for
 saving and retrieving definitions of data reconfigurations (forms).
 This section highlights connection protocols and requests.  The next
 section covers the Form Machine language in some detail.  File
 storage is not described in this document because it is transparent
 to the use of the service and its implementation is different at each
 DRS host.

CONCEPTUAL NETWORK CONNECTIONS

 There are three conceptual Network connections to the DRS, see Fig.
 1.
       1)  The control connection (CC) is between an originating user
           and the DRS.  A form specifying data reconfiguration is

Anderson, et al. [Page 3] RFC 138 Data Reconfiguration Service April 1971

           defined over this connection and is applied to data passing
           over the two connections described below.
       2)  The user connection (UC) is between a user process and the
           DRS.
       3)  The server connection (SC) is between the DRS and the
           serving process.
 Since the goal is to adapt the Network to user and server processes,
 a minimum of requirements are imposed on the UC and SC.
    +-------------+   CC   +-----------+   SC   +-----------+
    | ORIGINATING +--------+    DRS    +--------+ SERVER    |
    |    USER     |   ^    |           |    ^   | PROCESS   |
    +-------------+   |    +------+----+    |   +-----------+
                      |          /          |
                   Telnet       / <------ Simplex or Duplex
                  Protocol   UC/            Connections
                 Connection   /
                             /
                      +-----+-----+
                      | USER      |
                      | PROCESS   |
                      +-----------+
              Figure 1.  DRS Network Connections

CONNECTION PROTOCOLS AND MESSAGE FORMATS

 Over a control connection the dialog is directly between an
 originating user and the DRS.  Here the user is defining forms or
 assigning forms to connections for reformatting.
 The user connects to the DRS via the initial connection protocol
 (ICP) specified in NWG/RFC #80, version 1.  Rather than going through
 a logger, the user calls on a particular socket on which the DRS
 always listens.  DRS switches the user to another socket pair.
 Messages sent over a control connection are of the types and formats
 to be specified for TELNET.  Thus, a user at a terminal should be
 able to connect to a DRS via his local TELNET, for example, as shown
 in Fig.  2.

Anderson, et al. [Page 4] RFC 138 Data Reconfiguration Service April 1971

                                        +--------------+
                       +--------+  CC   |              |
               +-------+ TELNET +-------+     DRS      |
               |       +--------+       |              |
               |                        +--------------+
    +----------+---------+
    |      USER          |
    |(TERMINAL OR PROGRAM|
    +--------------------+
         Figure 2.  A TELNET Connection to DRS
 When a user connects to DRS he supplies a six-character user ID (UID)
 as a qualifier to guarantee the uniqueness of his form names.  He
 will have (at least) the following commands:
       1.  DEFFORM (name)
       2.  ENDFORM (name)
           These two commands define a form, the text of which is
           chronologically entered between them.  The (name) is six
           characters.  The form is stored in the DRS local file
           system.
       3.  PURGE (name)
           The named form, as qualified by the current UID, is purged
           from the DRS file system.
       4.  LISTNAMES (UID)
           The unqualified names of all forms assigned to UID are
           returned.
       5.  LISTFORM (name)
           The source text of a named form is returned.
       6.  DUPLEXCONNECT (user site, user send, user receive,
                      user method, server site, server
                      send, server receive, server method,
                      user-to-server form, server-to-user form)
       7.  SIMPLEXCONNECT (send site, send socket, send
                        method, receive site, receive
                        socket, receive method, form)

Anderson, et al. [Page 5] RFC 138 Data Reconfiguration Service April 1971

 Either one, both, or neither of the two parties specified in 6 or 7
 may be at the same host as the party issuing the request.  Sites and
 sockets specify user and server for the connection.  Method indicates
 the way in which the connection is established.  Three options are
 provided:
      1)  Site/socket already connected to DRS as a dummy
          control connection.  (A dummy control connection
          should not also be the real control connection.)
      2)  Connect via standard ICP. (Only for command no. 6.)
      3)  Connect directly via STR, RTS.

EXAMPLE CONNECTION CONFIGURATIONS

 There are basically two modes of DRS operation: 1) the user wishes to
 establish a DRS UC/SC connection(s) between two programs and 2) the
 user wants to establish the same connection(s) where he (his
 terminal) is at the end of the UC or the SC.  The latter case is
 appropriate when the user wishes to interact from his terminal with
 the serving process (e.g., a logger).
 In the first case (Fig. 1, where the originating user is either a
 terminal or a program) the user issues the appropriate CONNECT
 command.  The UC/SC can be simplex or duplex.
 The second case has two possible configurations, shown in Figs. 3 and
 4.
             +--------+  CC  +--------+      +------+
             |        +------+        |  SC  |      |
   +------+ /| TELNET |  UC  |  DRS   +------+  SP  |
   |      |/ |        +------+        |      |      |
   | USER | /+--------+      +--------+      +------+
   |      |/
   +------+
          Figure 3.  Use of Dummy Control Connection
             +--------+
   +------+ /|  USER  |  CC  +--------+      +------+
   |      |/ |  SIDE  +------+        |  SC  |      |
   | USER |  +--------+  UC  |  DRS   +------+  SP  |
   |      |\ | SERVING+------+        |      |      |
   +------+ \|  SIDE  |      +--------+      +------+
             +--------+
          Figure 4.  Use of Server TELNET

Anderson, et al. [Page 6] RFC 138 Data Reconfiguration Service April 1971

 In Fig. 3 the user instructs his TELNET to make two duplex
 connections to DRS.  One is used for control information (the CC) and
 the other is a dummy.  When he issues the CONNECT he references the
 dummy duplex connection (UC) using the "already connected" option.
 In Fig. 4 the user has his TELNET (user side) call the DRS.  When he
 issues the CONNECT the DRS calls the TELNET (server side) which
 accepts the call on behalf of the console.  This distinction is known
 only to the user since to the DRS the configuration in Fig. 4 appears
 identical to that in Fig. 1.  Two points should be noted:
      1)  TELNET protocol is needed only to define forms and direct
          connections.  It is not required for the using and serving
          processes.
      2)  The using and serving processes need only a minimum of
          modification for Network use, i.e., an NCP interface.

III. THE FORM MACHINE

INPUT/OUTPUT STREAMS AND FORMS

 This section describes the syntax and semantics of forms that specify
 the data reconfigurations.  The Form Machine gets an input stream,
 reformats the input stream according to a form describing the
 reconfiguration, and emits the reformatted data as an output stream.
 In reading this section it will be helpful to envision the
 application of a form to the data stream as depicted in Fig. 5.  An
 input stream pointer identifies the position of data (in the input
 stream) that is being analyzed at any given time by a part of the
 form.  Likewise, an output stream pointer locates data being emitted
 in the output stream.
     /\/\                                                  /\/\
^    |  |                     FORM                         |  |   ^
|    |  |                -----------------                 |  |   |
|    |  |            +-  -----------------  -+             |  |   |
|    |  |            |   CURRENT PART OF     |             |  |   |

INPUT | |⇐ CURRENT < —————– > CURRENT ⇒ | | OUTPUT STREAM | | POINTER | FORM BEING APPLIED | POINTER | | STREAM

     |  |            +-  -----------------  -+             |  |
     |  |                -----------------                 |  |
     |  |                -----------------                 |  |
     |  |                -----------------                 |  |
     \/\/                                                  \/\/
            Figure 5.  Application of Form to Data Streams

Anderson, et al. [Page 7] RFC 138 Data Reconfiguration Service April 1971

FORM MACHINE BNF SYNTAX

 form           ::=  rule | rule form
 rule           ;;=  label  inputstream  outputstream ;
 label          ::=  INTEGER | <null>
 inputstream    ::=  terms | <null>
 terms          ::=  term | terms , term
 outputstream   ::=  : terms | <null>
 term           ::=  identifier | identifier  descriptor |
                     descriptor | comparator
 identifier     ::=  an alpha character followed by 0 to 3
                     alphamerics
 descriptor     ::=  (replicationexpression , datatype ,
                     valueexpression , lengthexpression  control)
 comparator     ::=  (value  connective  value  control)  |
                     (identifier .<=>. control)
 replicationexpression  ::=  arithmeticexpression | <null>
 datatype       ::=  B | O | X | E | A
 valueexpression  ::=  value | <null>
 lengthexpression  ::=  # | arithmeticexpression | <null>
 connective     ::=  .LE. | .LT. | .GE. | .GT. | .EQ. | .NE.
 value          ::=  literal | arithmeticexpression
 arithmeticexpression  ::=  primary | primary operator
                            arithmeticexpression
 primary        ::=  identifier | L(identifier) | V(identifier) |
                     INTEGER
 operator       ::=  + | - | * | /
 literal        ::=  literaltype "string"

Anderson, et al. [Page 8] RFC 138 Data Reconfiguration Service April 1971

 literaltype    ::=  B | O | X | E | A
 string         ::=  from 0 to 256 characters
 control        ::=  :  options | <null>
 options        ::=  S(where) | F(where) | U(where) |
                     S(where) , F(where) |
                     F(where) , S(where)
 where          ::=  arithmeticexpression | R(arithmeticexpression)

ALTERNATE SPECIFICATION OF FORM MACHINE SYNTAX

                                 infinity

form ::= {rule}

                                 1
                                    1         1          1

rule ::= {INTEGER} {terms} {:terms} ;

                                    0         0          0
                                       infinity

terms ::= term {,term}

                                       0
                                                    1

term ::= identifier | {identifier} descriptor

                                                    0
                           | comparator
                                                  1

descriptor ::= ({arithmeticexpression} , datatype ,

                                                  0
                                  1                     1           1
                           {value} ,  {lengthexpression}  {:options}
                                  0                     0           0
                                                               1

comparator ::= (value connective value {:options} ) |

                                                               0
                                                            1
                           (identifier .<=. value {:options} )
                                                            0

connective ::= .LE. | .LT. | .GE. | .GT. | .EQ. | .NE.

lengthexpression ::= # | arithmeticexpression

datatype ::= B | O | X | E | A

value ::= literal | arithmeticexpression

Anderson, et al. [Page 9] RFC 138 Data Reconfiguration Service April 1971

                                                       infinity

arithmeticexpression ::= primary {operator primary}

operator ::= + | - | * | /

primary ::= identifier | L(identifier) |

                           V(identifier) | INTEGER
                                                    256

literal ::= literaltype "{CHARACTER} "

literaltype ::= B | O | X | A | E

                                               1

options ::= S(where) {,F(where)} |

                                               0
                                               1
                           F(where) {,S(where)}  | U(where)
                                               0

where ::= arithmeticexpression |

                           R(arithmeticexpression)
                                                   3

identifier ::= ALPHABETIC {ALPHAMERIC}

FORMS

 A form is an ordered set of rules.
       form ::=  rule | rule form
 The current rule is applied to the current position of the input
 stream.  If the (input stream part of a) rule fails to correctly
 describe the contents of the current input then another rule is made
 current and applied to the current position of the input stream.  The
 next rule to be made current is either explicitly specified by the
 current term in the current rule or it is the next sequential rule by
 default.  Flow of control is more fully described under TERM AND RULE
 SEQUENCING.
 If the (input stream part of a) rule succeeds in correctly describing
 the current input stream, then some data may be emitted at the
 current position in the output stream according to the rule.  The
 input and output stream pointers are advanced over the described and
 emitted data, respectively, and the next rule is applied to the now
 current position of the input stream.
 Application of the form is terminated when an explicit return
 (R(arithmeticexpression)) is encountered in a rule.  The user and

Anderson, et al. [Page 10] RFC 138 Data Reconfiguration Service April 1971

 server connections are closed and the return code
 (arithmeticexpression) is sent to the originating user.

RULES

 A rule is a replacement, comparison, and/or an assignment operation
 of the form shown below.
       rule ::= label  inputstream  outputstream ;
 A label is the name of a rule and it exists so that the rule may be
 referenced elsewhere in the form for explicit rule transfer of
 control.  Labels are of the form below.
       label ::=  INTEGER | <null>
 The optional integer labels are in the range 0 >= INTEGER >= 9999.
 The rules need not be labeled in ascending numerical order.

TERMS

 The inputstream (describing the input stream to be matched) and the
 outputstream (describing data to be emitted in the output stream)
 consist of zero or more terms and are of the form shown below.
       inputstream   ::=  terms | <null>
       outputstream  ::=  :terms | <null>
       terms         ::=  term | terms , term
 Terms are of one of four formats as indicated below.
       term ::=  identifier | identifier  descriptor |
                 descriptor | comparator

Term Format 1

 The first term format is shown below.
       identifier
 The identifier is a symbolic reference to a previously identified
 term (term format 2) in the form.  It takes on the same attributes
 (value, length, type) as the term by that name.  Term format 1 is
 normally used to emit data in the output stream.
 Identifiers are formed by an alpha character followed by 0 to 3
 alphameric characters.

Anderson, et al. [Page 11] RFC 138 Data Reconfiguration Service April 1971

Term Format 2

 The second term format is shown below.
       identifier descriptor
 Term format 2 is generally used as an input stream term but can be
 used as an output stream term.
 A descriptor is defined as shown below.
       descriptor ::= (replicationexpression, datatype,
                      valueexpression, lengthexpression
                      control)
 The identifier is the symbolic name of the term in the usual
 programming language sense.  It takes on the type, length, and value
 attributes of the term and it may be referenced elsewhere in the
 form.
 The replication expression is defined below.
       replicationexpression ::= arithmeticexpression | <null>
       arithmeticexpression ::= primary | primary operator
                                     arithmeticexpression
       operator ::= + | - | * | /
       primary ::= identifier | L(identifier) | V(identifier) |
                   INTEGER
 The replication expression is a repeat function applied to the
 combined data type and value expression.  It expresses the number of
 times that the value (of the data type/value expression) is to be
 repeated within the field length denoted by the data type/length
 expression.
 A null replication expression has the value of one.  Arithmetic
 expressions are evaluated from left-to-right with no precedence.  (It
 is anticipated that this interpretation might be changed, if
 necessary.)
 The L(identifier) is a length operator that generates a 32-bit binary
 integer corresponding to the length of the term named.  The
 V(identifier) is a value operator that generates a 32-bit binary
 integer corresponding to the value of the term named.  (See
 Restrictions and Interpretations of Term Functions.)  The value
 operator is intended to convert character strings to their numerical
 correspondents.

Anderson, et al. [Page 12] RFC 138 Data Reconfiguration Service April 1971

 The data type is defined below.
           datatype ::= B | O | X | E | A
 The data type describes the kind of data that the term represents.
 (It is expected that additional data types, such as floating point
 and user-defined types, will be added as needed.)
      Data Type         Meaning              Unit Length
          B             Bit string              1 bit
          O             Bit string              3 bits
          X             Bit string              4 bits
          E             EBCDIC character        8 bits
          A             Network ASCII character 8 bits
      The value expression is defined below.
               valueexpression ::= value | <null>
               value ::= literal | arithmeticexpression
               literal ::= literaltype "string"
               literaltype ::= B | O | X | E | A
 The value expression is the unit value of a term expressed in the
 format indicated by the data type.  It is repeated according to the
 replication expression, in a field whose length is constrained by the
 length expression.
 A null value expression in the input stream defaults to the data
 present in the input stream.  The data must comply with the datatype
 attribute, however.
 A null value expression generates padding according to Restrictions
 and Interpretations of Term Functions.
 The length expression is defined below.
       lengthexpression ::= # | arithmeticexpression | <null>
 The length expression states the length of the field containing the
 value expression as expanded by the replication expression.  If the
 value of the length expression is less then the length implied by the
 expanded value expression, then the expanded value expression is
 truncated, see Restrictions and Interpretations of Term Functions.
 The terminal symbol # means an arbitrary length, explicitly
 terminated by the value of the next term.  The # is legal only in the
 input stream and not in the output stream.

Anderson, et al. [Page 13] RFC 138 Data Reconfiguration Service April 1971

 If the length expression is less than or equal to zero, the term
 succeeds but the appropriate stream pointer is not advanced.
 Positive lengths cause the appropriate stream pointer to be advanced
 if the term otherwise succeeds.
 Control is defined under TERM AND RULE SEQUENCING.

Term Format 3

 Term format 3 is shown below.
       descriptor
 It is identical to term format 2 with the omission of the identifier.
 Term format 3 is generally used in the output stream.  It is used in
 the input stream where input data is to be passed over but not
 retained for emission or later reference.

Term Format 4

 The fourth term format is shown below.
       comparator    ::= (value connective value control) |
                         (identifier .<=. value control)
       value         ::= literal | arithmeticexpression
       literal       ::= literaltype "string"
       literaltype   ::= B | O | X | E | A
       string        ::= from 0 to 256 characters
       connective    ::= .LE. | .LT. | .GE. | .GT. | .EQ. | .NE.
 The fourth term format is used for assignment and comparison.
 The assignment operator .<=. assigns the value to the identifier.
 The connectives have their usual meaning.  Values to be compared must
 have the same type and length attributes or an error condition arises
 and the form fails.

The Application of a Term

 The elements of a term are applied by the following sequence of
 steps.
       1.  The data type and value expression together specify a unit
           value, call it x.
       2.  The replication expression specifies the number of times x
           is to be repeated (or copied) in concatenated fashion.  The
           value of the concatenated xs becomes, say, y of length L1.

Anderson, et al. [Page 14] RFC 138 Data Reconfiguration Service April 1971

       3.  The data type and the length expression together specify a
           field length of the input area (call it L2) that begins at
           the current stream pointer position.
       4.  The value of y is truncated to y' if L1 > L2.  Call the
           truncated length L1'.
       5.  If the term is an input stream term, then the value y' of
           length L1' is compared to the input value beginning at the
           current input pointer position.
       6.  If the values are identical over the length L1' then the
           input value of length L2 (may be greater than L1') starting
           at the current pointer position in the input area, becomes
           the value of the term.
 In an output stream term, the procedure is the same except that the
 source of input is the value of the term(s) named in the value
 expression and the data is emitted in the output stream.
 The above procedure is modified to include a one term look-ahead
 where lengths are indefinite because of the arbitrary symbol, #.

Restrictions and Interpretations of Term Functions

 1.  Terms specifying indefinite lengths, through the use of the #
       symbol must be separated by some type-specific data such as a
       literal.  (A literal isn't specifically required, however.  An
       arbitrary number of ASCII characters could be terminated by a
       non-ASCII character.)  # is legal only in the input stream, not
       in the output stream.
 2.  Truncation and padding is as follows:
       a)  Character to character (A <--> E) conversion is left
           justified and truncated or padded on the right with blanks.
       b)  Character to numeric and numeric to numeric conversions are
           right-justified and truncated or padded on the left with
           zeros.
       c)  Numeric to character conversion is right-justified and
           left-padded with blanks.
 3.  The following are ignored in a form definition over the control
       connection.
       a)  TAB, carriage return, etc.
       b)  blanks except within quotes.
       c)  /* string */ is treated as comments except within quotes.
 4.  The following defaults prevail where the term part is omitted.

Anderson, et al. [Page 15] RFC 138 Data Reconfiguration Service April 1971

       a)  The replication expression defaults to one.
       b)  The data type defaults to type B.
       c)  The value expression of an input stream term defaults to
           the value found in the input stream, but the input stream
           must conform to data type and length expression.  The value
           expression of an output stream term defaults to padding
           only.
       d)  The length expression defaults to the size of the quantity
           determined by replication expression, data type, and value
           expression.
       e)  Control defaults to the next sequential term if a term is
           successfully applied; else control defaults to the next
           sequential rule.  If _where_ evaluates to an undefined
           _label_ the form fails.
 5.  Arithmetic expressions are evaluated left-to-right with no
       precedence.
 6.  The following limits prevail.
       a)  Binary lengths are <= 32 bits
       b)  Character strings are <= 256 8-bit characters
       c)  Identifier names are <= 4 characters
       d)  Maximum number of identifiers is <= 256
       e)  Label integers are >= 0 and <= 9999
 7.  Value and length operators product 32-bit binary integers.  The
       value operator is currently intended for converting A or E type
       decimal character strings to their binary correspondents.  For
       example, the value of E'12' would be 0......01100.  The value
       of E'AB' would cause the form to fail.

Anderson, et al. [Page 16] RFC 138 Data Reconfiguration Service April 1971

TERM AND RULE SEQUENCING

 Sequencing may be explicitly controlled by including control in a
 term.
      control ::=  :options | <null>
      options ::=  S(where) | F(where) | U(where)
                   S(where) , F(where) |
                   F(where) , S(where)
      where   ::=  arithmeticexpression | R(arithmeticexpression)
 S, F, and U denote success, fail, and unconditional transfers,
 respectively.  _Where_ evaluates to a _rule_ label, thus transfer can
 be effected from within a rule (at the end of a term) to the
 beginning of another rule.  R means terminate the form and return the
 evaluated expression to the initiator over the control connection (if
 still open).
 If terms are not explicitly sequenced, the following defaults
 prevail.
 1)  When a term fails go to the next sequential rule.
 2)  When a term succeeds go to the next sequential
     term within the rule.
 (3) At the end of a rule, go to the next sequential
     rule.
 Note in the following example, the correlation between transfer of
 control and movement of the input pointer.
      1   XYZ(,B,,8:S(2),F(3)) : XYZ ;
      2   . . . . . . .
      3   . . . . . . .
 The value of XYZ will never be emitted in the output stream since
 control is transferred out of the rule upon either success or
 failure.  If the term succeeds, the 8 bits of input will be assigned
 as the value of XYZ and rule 2 will then be applied to the same input
 stream data.  That is, since the complete rule 1 was not successfully
 applied, then the input stream pointer is not advanced.

Anderson, et al. [Page 17] RFC 138 Data Reconfiguration Service April 1971

IV. EXAMPLES

REMARKS

 The following examples (forms and also single rules) are simple
 representative uses of the Form Machine.  The examples are expressed
 in a term-per-line format only to aid the explanation.  Typically, a
 single rule might be written as a single line.

FIELD INSERTION

 To insert a field, separate the input into the two terms to allow the
 inserted field between them.  For example, to do line numbering for a
 121 character/line printer with a leading carriage control character,
 use the following form.
 (NUMB.<=>.1);       /*initialize line number counter to one*/
 1 CC(,E,,1:F(R(99))),  /*pick up control character and save
                          as CC*/
                        /*return a code of 99 upon exhaustion*/
 LINE(,E,,121 : F(R(98)))    /*save text as LINE*/
 :CC,               /*emit control character*/
 (,E,NUMB,2),       /*emit counter in first two columns*/
 (,E,E".",1),       /*emit period after line number*/
 (,E,LINE,117),     /*emit text, truncated in 117 byte field*/
 (NUMB.<=.NUMB+1:U(1));    /*increment line counter and go to
                             rule one*/;;

DELETION

 Data to be deleted should be isolated as separate terms on the left,
 so they may be omitted (by not emitting them) on the right.
 (,B,,8),           /*isolate 8 bits to ignore*/
 SAVE(,A,,10)       /*extract 10 ASCII characters from
                      input stream*/
 :(,E,SAVE,);      /*emit the characters in SAVE as EBCDIC
                     characters whose length defaults to the
                     length of SAVE, i.e., 10, and advance to
                     the next rule*/
 In the above example, if either input stream term fails,
 the next sequential rule is applied.

VARIABLE LENGTH RECORDS

 Some devices, terminals and programs generate variable length
 records.  To following rule picks up variable length EBCDIC records

Anderson, et al. [Page 18] RFC 138 Data Reconfiguration Service April 1971

 and translates them to ASCII.
 CHAR(,E,,#),       /*pick up all (an arbitrary number of)
                      EBCDIC characters in the input stream*/
 (,X,X"FF",2)       /*followed by a hexadecimal literal,
                      FF (terminal signal)*/
 :(,A,CHAR,),       /*emit them as ASCII*/
 (,X,X"25",2);      /*emit an ASCII carriage return*/

STRING LENGTH COMPUTATION

 It is often necessary to prefix a length field to an arbitrarily long
 character string.  The following rule prefixes an EBCDIC string with
 a one-byte length field.
 Q(,E,,#),          /*pick up all EBCDIC characters*/
 TS(,X,X"FF",2)     /*followed by a hexadecimal literal, FF*/
 :(,B,L(Q)+2,8),    /*emit the length of the characters
                      plus the length of the literal plus
                      the length of the count field itself,
                      in an 8-bit field*/
 Q,                 */emit the characters*/
 TS;                */emit the terminal*/

TRANSPOSITION

 It is often desirable to reorder fields, such as the following
 example.
 Q(,E,,20), R(,E,,10) , S(,E,,15), T(,E,,5) : R, T, S, Q ;
 The terms are emitted in a different order.

CHARACTER PACKING AND UNPACKING

 In systems such as HASP, repeated sequences of characters are packed
 into a count followed by the character, for more efficient storage
 and transmission.  The first form packs multiple characters and the

Anderson, et al. [Page 19] RFC 138 Data Reconfiguration Service April 1971

 second unpacks them.
 /*form to pack EBCDIC streams*/
 /*returns 99 if OK, input exhausted*/
 /*returns 98 if illegal EBCDIC*/
 /*look for terminal signal FF which is not a legal EBCDIC*/
 /*duplication count must be 0-254*/
 1 (,X,X"FF",2 : S(R(99))) ;
 /*pick up the EBCDIC and initialize count/*
   CHAR(,E,,1 : F(R(98))) , (CNT .<=. 1) ;
 /*count consecutive EBCDICs like CHAR*/
 2 (,E,CHAR,1 : F(3)) , (CNT .<=. CNT+1 : U(2)) ;
 /*emit count and current character*/
 3 : (,B,CNT,8), CHAR, (:U(1));
 /*end of form*/;;
 /*form to unpack EBCDIC streams*/
 /*look for terminal*/
 1 (,X,X"FF",2 : S(R(99))) ;
 /*emit character the number of times indicated*/
 /*by the counter contents*/
 CNT(,B,,8), CHAR(,E,,1) : (CNT,E,CHAR,CNT:U(1));
 /*failure of form*/
 (:U(R(98))) ;;

V. PROPOSED USES OF DATA RECONFIGURATION SERVICE

 The following are some proposed uses of the DRS that were submitted
 by the sites indicated.
 UCLA
 1.  Pack/unpack text files.
 2.  Preprocessor to scan META compiler input.
 3.  Perhaps graphics.
 MIT
 1.  Reformatting within file transfer service.
 2.  Character conversions.
 3.  Possible graphics service (Evans and Sutherland output
     format).
 4.  Reformat arguments of subroutines remote to each other.
 U. OF ILLINOIS
 1.  Dependent upon remote use of DRS for many remote
     services.
 SDC
 1.  Would be essential to data transfer in general.

Anderson, et al. [Page 20] RFC 138 Data Reconfiguration Service April 1971

 2.  Could be used in relation to data management language.
 UCSB
 1.  Checkout of I/O formats of file system.
 2.  Debugging Network services in general.
 3.  Mapping their services into future standards.
 RAND
 1.  To describe RJO/RJE message formats at UCSB.
 2.  To describe RJS message formats at UCLA.
 3.  To adapt Network to existing services, in general.
 MITRE
 1.  Character conversions.
 2.  Testing data formats going into data bases for correct
     field formatting.
 VI.  IMPLEMENTATION PLANS
 Four sites currently plan to implement and offer the service on an
 experimental basis.
 1.  MIT    Implementation of forms interpreter in MIDAS
            (assembly).  Perhaps Tree Meta compiler of
            forms.  Implementation on PDP-10.
 2.  UCLA   Implementation on SIGMA-7 employing META-7
            to compile forms.
 3.  UCSB   Implementation on 360/75.
 4.  RAND   Initial implementation on 360/65; compiler to be written
             in graphics CPS; compiled intermediate forms to be
             interpreted by assembler language subroutine.  Later
             implemented on PDP-10.
 In addition to the above sites, the University of Illinois and Mitre
 plan to experiment with the service.

Anderson, et al. [Page 21] RFC 138 Data Reconfiguration Service April 1971

                              APPENDIX A

Note 1 to the DRS Working Group

 As you recall, we spent considerable time in discussing the use and
 meaning of the arbitrary symbol, #.  To summarize, it was clear that
 inclusion of the # in both replication and length expressions led to
 ambiguities.  We settled on its restricted use in the length
 expression of an input term, although no one was entirely satisfied
 with this definition.
 Recently, Jim White has again commented on the #.  Jim feels that it
 is curious that one can pick up an arbitrary number of EBCDIC
 characters, for example, but can't pick up an arbitrary number of
 specific EBCDIC characters such as EBCDIC A's.  Jim feels that a more
 natural way to interpret the length, value, and replication
 expressions would be as the IBM OS assembler interprets the
 attributes of the pseudo instruction, define constant (CD).
 The IBM OS assembler uses the following format.
      1             2              3           4
 duplication       type        modifiers   nominal value
   factor
 The duplication factor, if specified, causes the constant to be
 generated the number of times indicated by the factor.  The type
 defines the type of constant being specified.  Modifiers describe the
 length, scaling, and exponent of the constant.  Nominal value
 supplies the constant described by the subfields that precede it.
 Assume that we use the # only as a duplication factor (replication
 expression).  Hence, in the example of the form to pack EBCDIC
 characters, the counter and looping can be eliminated.
 CHAR(,E,,1) ;
 LEN(#,#,CHAR,1) : (,B,L(LEN)+1,*) , CHAR ;
 The interpretation is that the data type, length expression, and
 value expression make up the unit value.  This quantity can then be
 replicated.  As our document now stands, only the data type and value
 expression make up the unit value.
 The application of a term according to Jim's suggestion is as
 follows.
 1.  The data type, value expression, and length expression together
     specify a unit value, call it x.

Anderson, et al. [Page 22] RFC 138 Data Reconfiguration Service April 1971

 2.  The replication expression specifies the number of times x is to
     be repeated.  The value of the concatenated xs becomes y of
     length L.
 3.  If the term is an input stream term then the value beginning at
     the current input pointer position.
 4.  If the input value satisfies the constraints of y over length L
     then the input value of length L becomes the value of the term.

Note 2 to the DRS Working Group

 There has been recent debate of whether the input pointer should be
 advanced upon successful completion of a rule (as it now is defined)
 or upon successful completion of each term.  See the example on page
 22.  If the input pointer is advanced upon successful completion of a
 term, then rules become equivalent to terms.
 I would like to for us to discuss at the SJCC both the term
 attributes and the input pointer advance issues.
                                              John
     [ This RFC was put into machine readable form for entry ]
     [ into the online RFC archives by Katsunori Tanaka 4/99 ]

Anderson, et al. [Page 23]

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