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Network Working Group                                          A. Newton
Internet-Draft                                                      ARIN
Intended status: Standards Track                              P. Cordell
Expires: April 1, 2018                                         Codalogic
                                                      September 28, 2017


              A Language for Rules Describing JSON Content
                   draft-newton-json-content-rules-09

Abstract

   This document describes a language for specifying and testing the
   expected content of JSON structures found in JSON-using protocols,
   software, and processes.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 1, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  A First Example: Specifying Content . . . . . . . . . . .   3
     1.2.  A Second Example: Testing Content . . . . . . . . . . . .   3
   2.  Overview of the Language  . . . . . . . . . . . . . . . . . .   5
   3.  Lines and Comments  . . . . . . . . . . . . . . . . . . . . .   7
   4.  Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Rule Names and Assignments  . . . . . . . . . . . . . . .   8
     4.2.  Annotations . . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Starting Points and Root Rules  . . . . . . . . . . . . .  10
     4.4.  Type Specifications . . . . . . . . . . . . . . . . . . .  10
     4.5.  Primitive Specifications  . . . . . . . . . . . . . . . .  12
       4.5.1.  Numbers, Booleans and Null  . . . . . . . . . . . . .  12
       4.5.2.  Strings . . . . . . . . . . . . . . . . . . . . . . .  13
     4.6.  Any Type  . . . . . . . . . . . . . . . . . . . . . . . .  16
     4.7.  Member Specifications . . . . . . . . . . . . . . . . . .  16
     4.8.  Object Specifications . . . . . . . . . . . . . . . . . .  16
     4.9.  Array Specifications  . . . . . . . . . . . . . . . . . .  19
       4.9.1.  Unordered Array Specifications  . . . . . . . . . . .  21
     4.10. Group Specifications  . . . . . . . . . . . . . . . . . .  21
     4.11. Ordered and Unordered Groups in Arrays  . . . . . . . . .  22
     4.12. Sequence and Choice Combinations in Array, Object, and
           Group Specifications  . . . . . . . . . . . . . . . . . .  22
     4.13. Repetition in Array, Object, and Group Specifications . .  23
     4.14. Negating Evaluation . . . . . . . . . . . . . . . . . . .  25
   5.  Directives  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     5.1.  jcr-version . . . . . . . . . . . . . . . . . . . . . . .  26
     5.2.  ruleset-id  . . . . . . . . . . . . . . . . . . . . . . .  27
     5.3.  import  . . . . . . . . . . . . . . . . . . . . . . . . .  27
   6.  Tips and Tricks . . . . . . . . . . . . . . . . . . . . . . .  28
     6.1.  Any Member with Any Value . . . . . . . . . . . . . . . .  28
     6.2.  Lists of Values . . . . . . . . . . . . . . . . . . . . .  29
     6.3.  Groups in Arrays  . . . . . . . . . . . . . . . . . . . .  29
     6.4.  Groups in Objects . . . . . . . . . . . . . . . . . . . .  30
     6.5.  Group Rules as Macros . . . . . . . . . . . . . . . . . .  31
     6.6.  Object Mixins . . . . . . . . . . . . . . . . . . . . . .  31
     6.7.  Subordinate Dependencies  . . . . . . . . . . . . . . . .  31
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  32
     7.1.  JCR Validator . . . . . . . . . . . . . . . . . . . . . .  32
     7.2.  Codalogic JCR Parser  . . . . . . . . . . . . . . . . . .  33
     7.3.  JCR Java  . . . . . . . . . . . . . . . . . . . . . . . .  33
   8.  ABNF Syntax . . . . . . . . . . . . . . . . . . . . . . . . .  33
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  39
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  39
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  39
     10.2.  Infomative References  . . . . . . . . . . . . . . . . .  40
     10.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  40



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   Appendix A.  Co-Constraints . . . . . . . . . . . . . . . . . . .  40
   Appendix B.  Testing Against JSON Content Rules . . . . . . . . .  41
     B.1.  Locally Overriding Rules  . . . . . . . . . . . . . . . .  41
     B.2.  Rule Callbacks  . . . . . . . . . . . . . . . . . . . . .  42
   Appendix C.  Changes from -07 and -08 . . . . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

1.  Introduction

   This document describes JSON Content Rules (JCR), a language for
   specifying and testing the interchange of data in JSON [RFC7159]
   format used by computer protocols and processes.  The syntax of JCR
   is not JSON but is "JSON-like", possessing the conciseness and
   utility that has made JSON popular.

1.1.  A First Example: Specifying Content

   The following JSON data describes a JSON object with two members,
   "line-count" and "word-count", each containing an integer.

               { "line-count" : 3426, "word-count" : 27886 }

                                 Figure 1

   This is also JCR that describes a JSON object with a member named
   "line-count" that is an integer that is exactly 3426 and a member
   named "word-count" that is an integer that is exactly 27886.

   For a protocol specification, it is probably more useful to specify
   that each member is any integer and not specific, exact integers:

            { "line-count" : integer, "word-count" : integer }

                                 Figure 2

   Since line counts and word counts should be either zero or a positive
   integer, the specification may be further narrowed:

                { "line-count" : 0.. , "word-count" : 0.. }

                                 Figure 3

1.2.  A Second Example: Testing Content

   Building on the first example, this second example describes the same
   object but with the addition of another member, "file-name".





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                      {
                        "file-name"  : "rfc7159.txt",
                        "line-count" : 3426,
                        "word-count" : 27886
                      }

                                 Figure 4

   The following JCR describes objects like it.

                         {
                           "file-name"  : string,
                           "line-count" : 0..,
                           "word-count" : 0..
                         }

                                 Figure 5

   For the purposes of writing a protocol specification, JCR may be
   broken down into named rules to reduce complexity and to enable re-
   use.  The following example takes the JCR from above and rewrites the
   members as named rules.

                        {
                          $fn,
                          $lc,
                          $wc
                        }

                        $fn = "file-name"  : string
                        $lc = "line-count" : 0..
                        $wc = "word-count" : 0..

                                 Figure 6

   With each member specified as a named rule, software testers can
   override them locally for specific test cases.  In the following
   example, the named rules are locally overridden for the test case
   where the file name is "rfc4627.txt".

                    $fn = "file-name"  : "rfc4627.txt"
                    $lc = "line-count" : 2102
                    $wc = "word-count" : 16714

                                 Figure 7






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   In this example, the protocol specification describes the JSON object
   in general and an implementation overrides the rules for testing
   specific cases.

   All figures used in this specification are available here [1].

2.  Overview of the Language

   JCR is composed of rules (as the name suggests).  A collection of
   rules that is processed together is a ruleset.  Rulesets may also
   contain comments, blank lines, and directives that apply to the
   processing of a ruleset.

   Rules are composed of two parts, an optional rule name and a rule
   specification.  A rule specification can be either a type
   specification or a member specification.  A member specification
   consists of a member name specification and a type specification.

   A type specification is used to specify constraints on a superset of
   a JSON value (e.g. number / string / object / array etc.).  In
   addition to defining primitive types (such as string or integer),
   array types, and object types, type specifications may define the JCR
   specific concept of group types.

   Type specifications corresponding to arrays, objects and groups may
   be composed of other rule specifications.

   A member specification is used to specify constraints on a JSON
   member (i.e. members of a JSON object).

   Rules with rule name assignments may be referenced in place of type
   specifications and member specifications.

   Rules may be defined across line boundaries and there is no line
   continuation syntax.

   Any rule consisting only of a type specification is considered a root
   rule.  Unless otherwise specified, all the root rules of a ruleset
   are evaluated against a JSON instance or document.

   Putting it all together, Figure 9 describes the JSON in Figure 8.










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   Example JSON shamelessly lifted from RFC 4627

         {
           "Image": {
             "Width":  800,
             "Height": 600,
             "Title":  "View from 15th Floor",
             "Thumbnail": {
               "Url":    "http://www.example.com/image/481989943",
               "Height": 125,
               "Width":  100
             },
             "IDs": [116, 943, 234, 38793]
           }
         }

                                 Figure 8


































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   Rules describing Figure 8

             ; the root of the JSON instance is an object
             ; this root rule describes that object
             {

               ; the object specification contains
               ; one member specification
               "Image" : {

                 ; $width and $height are defined below
                 $width,
                 $height,

                 ; "Title" member specification
                 "Title" :string,

                 ; "Thumbnail" member specification, which
                 ; defines an object
                 "Thumbnail":  {

                   ; $width and $height are re-used again
                   $width, $height,

                   "Url" :uri
                 },

                 ; "IDs" member that is an array of
                 ; one ore more integers
                 "IDs" : [ integer * ]

               }
             }

             ; The definitions of the rules $width and $height
             $width  = "Width" : 0..1280
             $height = "Height" : 0..1024


                                 Figure 9

3.  Lines and Comments

   There is no statement terminator and therefore no need for a line
   continuation syntax.  Rules may be defined across line boundaries.
   Blank lines are allowed.





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   Comments are the same as comments in ABNF [RFC4234].  They start with
   a semi-colon (';') and continue to the end of the line.

4.  Rules

   Rules have two main components, an optional rule name assignment and
   a type or member specification.

   Type specifications define arrays, objects, etc... of JSON and may
   reference other rules using rule names.  Most type specifications can
   be defined with repetitions for specifying the frequency of the type
   being defined.  In addition to the type specifications describing
   JSON types, there is an additional group specification for grouping
   types.

   Member specifications define members of JSON objects, and are
   composed of a member name specification and either a type
   specification or a rule name referencing a type specification.

   Rules may also contain annotations which may affect the evaluation of
   all or part of a rule.  Rules without a rule name assignment are
   considered root rules, though rules with a rule name assignment can
   be considered a root rule with the appropriate annotation.

   Type specifications, depending on their type, can contain zero or
   more other specifications or rule names.  For example, an object
   specification might contain multiple member specifications or rule
   names that resolve to member specifications or a mixture of member
   specifications and rule names.  For the purposes of this document,
   specifications and rule names composing other specifications are
   called subordinate components.

4.1.  Rule Names and Assignments

   Rule names are signified with the dollar character ('$'), which is
   not part of the rule name itself.  Rule names have two components, an
   optional ruleset identifier alias and a local rule name.

   Local rule names must start with an alphabetic character (a-z,A-Z)
   and must contain only alphabetic characters, numeric characters, the
   hyphen character ('-') and the underscore character ('_').  Local
   rule names are case sensitive, and must be unique within a ruleset
   (that is, no two rule name assignments may use the same local rule
   name).

   Ruleset identifier aliases enable referencing rules from another
   ruleset.  They are not allowed in rule name assignments, and only
   found in rule names referencing other rules.  Ruleset identifiers



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   must start with an alphabetic character and contain no whitespace.
   Ruleset identifiers are case sensitive.  Simple use cases of JCR will
   most likely not use ruleset identifiers.

   In Figure 10 below, "http://ietf.org/rfcYYYY.JCR" and
   "http://ietf.org/rfcXXXX.JCR" are ruleset identifiers and "rfcXXXX"
   is a ruleset identifier alias.

          # ruleset-id http://ietf.org/rfcYYYY.JCR
          # import http://ietf.org/rfcXXXX.JCR as rfcXXXX
          $my_encodings  = ( "mythic" | "magic" )
          $all_encodings = ( $rfcXXXX.encodings | $my_encodings )

                                 Figure 10

   There are two forms of rule name assignments: assignments of
   primitive types and assignments of all other types.  Rule name
   assignments to primitive type specifications separate the rule name
   from the type specification with the character sequence '=:', whereas
   rule name assignments for all other type specifications only require
   the separation using the '=' character.

                ;rule name assignments for primitive types
                $foo         =: "foo"
                $some_string =: string

                ;rule name assignments for arrays
                $bar = [ integer, integer, integer ]

                ;rule name assignement for objects
                $bob = { "bar" : $bar, "foo" : $foo }


                                 Figure 11

   This is the one little "gotcha" in JCR.  This syntax is necessary so
   that JCR parsers may readily distinguish between rule name
   assignments involving string and regular expressions primitive types
   and member names of member specifications.

4.2.  Annotations

   Annotations may appear before a rule name assignment, before a type
   or member specification, or before a rule name contained within a
   type specification.  In each place, there may be zero or more
   annotations.  Each annotation begins with the character sequence "@{"
   and ends with "}".  The following is an example of a type
   specification with the not annotation (explained in Section 4.14):



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                     @{not} [ "fruits", "vegatables" ]

                                 Figure 12

   This specification defines the annotations "root", "not", and
   "unordered", but other annotations may be defined for other purposes.

4.3.  Starting Points and Root Rules

   Evaluation of a JSON instance or document against a ruleset begins
   with the evaluation of a root rule or set of root rules.  If no root
   rule (or rules) is specified locally at runtime, the set of root
   rules specified in the ruleset are evaluated.  The order of
   evaluation is undefined.

   The set of root rules specified in a ruleset is composed of all rules
   without a rule name assignment and all rules annotated with the
   "@{root}" annotation.

   The "@{root}" annotation may either appear before a rule name
   assignment or before a type definition.  It is ignored if present
   before referenced rule name inside of a type specification.

4.4.  Type Specifications

   The syntax of each type of type specifications varies depending on
   the type:
























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      ; primitive types can be string
      ; or number literals
      ; or number ranges
      "foo"
      2
      1..10

      ; primitive types can also be more generalized types
      string
      integer

      ; primitive type rules may be named
      $my_int =: 12

      ; member specifications consist of a member name
      ; followed by a colon and then followed by another
      ; type specification or a rule name
      ; (example shown with a rule name assignment)
      $mem1 = "bar" : "baz"
      $mem2 = "fizz" : $my_int

      ; member names may either be quoted strings
      ; or regular expressions
      ; (example shown with a rule name assignment)
      $mem3 = /^dev[0-9]$/ : 0..4096

      ; object specifications start and end with "curly braces"
      ; object specifications contain zero
      ; or more member specifications
      ; or rule names which reference a member specification
      { $mem1, "foo" : "fuzz", "fizz" : $my_int }

      ; array specifications start and end with square brackets
      ; array specifications contain zero
      ; or more non-member type specifications
      [ 1, 2, 3, $my_int ]

      ; finally, group specifications start and end with parenthesis
      ; groups contain other type specifications
      ( [ integer, integer], $rule1 )
      $rule1 = [ string, string ]

                                 Figure 13








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4.5.  Primitive Specifications

   Primitive type specifications define content for JSON numbers,
   booleans, strings, and null.

4.5.1.  Numbers, Booleans and Null

   The rules for booleans and null are the simplest and take the
   following forms:

                                  true
                                  false
                                  boolean
                                  null

                                 Figure 14

   Rules for numbers can specify the number be either an integer or
   floating point number:

                                  integer
                                  float
                                  double

                                 Figure 15

   The keyword 'float' represents a single precision IEEE-754 floating
   point number represented in decimal.  The keyword 'double' represents
   a double precision IEEE-754 floating point number represented in
   decimal format.

   Numbers may also be specified as an absolute value or a range of
   possible values, where a range may be specified using a minimum,
   maximum, or both:

                                   n
                                   n..m
                                    ..m
                                   n..
                                 n.f
                                 n.f..m.f
                                    ..m.f
                                 n.f..

                                 Figure 16

   When specifying a minimum and a maximum, both must either be an
   integer or a floating point number.  Thus to specify a floating point



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   number between zero and ten a definition of the following form is
   used:

                                 0.0..10.0


                                 Figure 17

   Integers may also be specified as ranges using bit lengths preceded
   by the 'int' or 'uint' words (i.e. 'int8', 'uint16').  The 'int'
   prefix specifies the integer as being signed whereas the 'uint'
   prefix specifies the integer as being unsigned.

                ; 0..255
                uint8

                ; -32768..32767
                int16

                ; 0..65535
                uint16

                ; -9223372036854775808..9223372036854775807
                int64

                ; 0..18446744073709551615
                uint64

                                 Figure 18

4.5.2.  Strings

   JCR provides a large number of data types to define the contents of
   JSON strings.  Generically, a string may be specified using the word
   'string'.  String literals may be specified using a double quote
   character followed by the literal content followed by another double
   quote.  And regular expressions may be specified by enclosing a
   regular expression within the forward slash ('/') character.













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                          ; any string
                          string

                          ; a string literal
                          "she sells sea shells"

                          ; a regular expression
                          /^she sells .*/

                                 Figure 19

   Regular expressions are not implicitly anchored and therefore must be
   explicitly anchored if necessary.

   A string can be specified as a URI [RFC3986] using the word 'uri',
   but also may be more narrowly scoped to a URI of a specific scheme.
   Specific URI schemes are specified with the word 'uri' followed by
   two period characters ('..') followed by the URI scheme.

                     ; any URI
                     uri

                     ;a URI narrowed for an HTTPS uri
                     uri..https

                                 Figure 20

   IP addresses may be specified with either the word 'ipv4' for IPv4
   addresses [RFC1166] or the word 'ipv6' for IPv6 addresses [RFC5952].
   Fully qualified A-label and U-label domain names may be specified
   with the words 'fqdn' and 'idn'.

   Dates and time can be specified as formats found in RFC 3339
   [RFC3339].  The word 'date' corresponds to the full-date ABNF rule,
   the word 'time' corresponds to the full-time ABNF rule, and the word
   'datetime' corresponds to the 'date-time' ABNF rule.

   Email addresses formatted according to RFC 5322 [RFC5322] may be
   specified using the 'email' word, and E.123 phone numbers may be
   specified using the word 'phone'.











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                         ;IP addresses
                         ipv4
                         ipv6
                         ipaddr

                         ;domain names
                         fqdn
                         idn

                         ; RFC 3339 full-date
                         date
                         ; RFC 3339 full-time
                         time
                         ; RFC 3339 date-time
                         datetime

                         ; RFC 5322 email address
                         email

                         ; phone number
                         phone

                                 Figure 21

   Binary data can be specified in string form using the encodings
   specified in RFC 4648 [RFC4648].  The word 'hex' corresponds to
   base16, while 'base32', 'base32hex', 'base64', and 'base64url'
   correspond with their RFC 4648 counterparts accordingly.

                           ; RFC 4648 base16
                           hex

                           ; RFC 4648 base32
                           base32

                           ; RFC 4648 base32hex
                           base32hex

                           ; RFC 4648 base64
                           base64

                           ; RFC 4648 base64url
                           base64url

                                 Figure 22






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4.6.  Any Type

   It is possible to specify that a value can be of any type allowable
   by JSON using the word 'any'.  The 'any' type specifies any primitive
   type, array, or object.

4.7.  Member Specifications

   Member specifications define members of JSON objects.  Unlike other
   type specifications, member specifications cannot be root rules and
   must be part of an object specification or preceded by a rule name
   assignment.

   Member specifications consist of a member name specification followed
   by a colon character (':') followed by either a subordinate
   component, which is either a rule name or a primitive, object, array,
   or group specification.  Member name specifications can be given
   either as a quoted string using double quotes or as a regular
   expression using forward slash ('/') characters.  Regular expressions
   are not implicitly anchored and therefore must have explicit anchors
   if needed.

            ;member name will exactly match "locationURI"
            $location_uri = "locationURI" : uri

            ;member name will match "eth0", "eth1", ... "eth9"
            $iface_mappings = /^eth[0-9]$/  : ipv4

                                 Figure 23

4.8.  Object Specifications

   Object specifications define JSON objects and are composed of zero or
   more subordinate components, each of which can be either a rule name,
   member specification, or group specification.  The subordinate
   components are enclosed at the start with a left curly brace
   character ('{') and at the end with a right curly brace character
   ('}').

   Evaluation of the subordinate components of object specifications is
   as follows:

   o  No order is implied for the members of the object being evaluated.

   o  Subordinate components of the object specification are evaluated
      in the order they appear.





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   o  Each member of the object being evaluated can only match one
      subordinate component.

   o  Any members not matched against a subordinate component are
      ignored.

   The following examples illustrate matching of JSON objects to JCR
   object specifications.

   As order is not implied for the members of objects under evaluation,
   the following rule will match the JSON in Figure 25 and Figure 26.

              { "locationUri" : uri, "statusCode" : integer }

                                 Figure 24

       { "locationUri" : "http://example.com", "statusCode" : 200 }

                                 Figure 25

       { "statusCode" : 200, "locationUri" : "http://example.com" }

                                 Figure 26




























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   Because subordinate components of an object specification are
   evaluated in the order in which they are specified (i.e. left to
   right, top to bottom) and object members can only match one
   subordinate component of an object specification, the rule o1 below
   will not match against the JSON in Figure 28 but the rule o2 below
   will match it.

             ; zero or more members that match "p0", "p1", etc
             ; and a member that matches "p1"
             $o1 = { /^p\d+$/ : integer *, "p1" : integer }

             ; a member that matches "p1" and
             ; zero or more members that match "p0", "p1", etc
             $o2 = { "p1" : integer, /^p\d+$/ : integer * }

   The first subordinate of rule o1 specifies that an object can have
   zero or more members (that is the meaning of "*", see Section 4.13)
   where the member name is the letter 'p' followed by a number (e.g.
   "p0", "p1", "p2"), and the second rule specifies a member with the
   exact member name of "p1".  Rule o2 has the exact same member
   specifications but in the opposite order.  Figure 28 does not match
   rule o1 because all of the members match the first subordinate rule
   leaving none to match the second subordinate rule.  However, rule o2
   does match because the first subordinate rule matches only one member
   of the JSON object allowing the second subordinate rule to match the
   other member of the JSON object.

                                 Figure 27

                          { "p0" : 1, "p1" : 2 }

                                 Figure 28

   As stated above, members of objects which do not match a rule are
   ignored.  The reason for this validation model is due to the nature
   of the typical access model to JSON objects in many programming
   languages, where members of the object are obtained by referencing
   the member name.  Therefore extra members may exist without harm.

   However, some specifications may need to restrict the members of a
   JSON object to a known set.  To construct a rule specifying that no
   extra members are expected, the @{not} annotation (see Section 4.14)
   may be used with a "match-all" regular expression as the last
   subordinate component of the object specification.







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   The following rule will match the JSON object in Figure 30 but will
   not match the JSON object in Figure 31.

                { "foo" : 1, "bar" : 2, @{not} // : any + }

                                 Figure 29

                         { "foo" : 1, "bar" : 2 }

                                 Figure 30

                    { "foo" : 1, "bar" : 2, "baz" : 3 }

                                 Figure 31

   This works because subordinate components are evaluated in the order
   they appear in the object rule, and the last component accepts any
   member with any type but fails to validate if one or more of those
   components are found due to the @{not} annotation.

4.9.  Array Specifications

   Array specifications define JSON arrays and are composed of zero or
   more subordinate components, each of which can either be a rule name
   or a primitive, array, object or group specification.  The
   subordinate components are enclosed at the start with a left square
   brace character ('[') and at the end with a right square brace
   character (']').

   Evaluation of the subordinate components of array specifications is
   as follows:

   o  The order of array items is implied unless the @{unordered}
      annotation is present.

   o  Subordinate components of the array specification are evaluated in
      the order they appear.

   o  Each item of the array being evaluated can only match one
      subordinate component of the array specification.

   o  If any items of the array are not matched, then the array does not
      match the array specification.

   These rules are further explained in the examples below.






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                            [ 0..1024, 0..980 ]

                                 Figure 32

   Unlike object specifications, order is implied in array
   specifications by default.  That is, the first subordinate component
   will match the first element of the array, the second subordinate
   component will match the second element of the array, and so on.

   Take for example the following ruleset:

           ; the first element of the array is to be a string
           ; the second element of the array is to be an integer
           $a1 = [ string, integer ]

           ; the first element of the array is to be an integer
           ; the second element of the array is to be a string
           $a2 = [ integer, string ]

                                 Figure 33

   It defines two rules, a1 and a2.  The array in the following JSON
   will not match a1, but will match a2.

                            [ 24, "Bob Smurd" ]

                                 Figure 34

   If an array has more elements than can be matched from the array
   specification, the array does not match the array specification.  Or
   stated differently, an array with unmatched elements does not
   validate.  Using the example array rule a2 from above, the following
   array does not match because the last element of the array does not
   match any subordinate component:

            [ 24, "Bob Smurd", "http://example.com/bob_smurd" ]

                                 Figure 35

   To allow an array to contain any value after guaranteeing that it
   contains the necessary items, the last subordinate component of the
   array specification should accept any item:









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           ; the first element of the array is to be an integer
           ; the second element of the array is to be a string
           ; anything else can follow
           $a3 = [ integer, string, any * ]

   The JSON array in Figure 35 will validate against the a3 rule in this
   example.

                                 Figure 36

4.9.1.  Unordered Array Specifications

   Array specifications can be made to behave in a similar fashion to
   object specifications with regard to the order of matching with the
   @{unordered} annotation.

   In the ruleset below, a1 and a2 have the same subordinate components
   given in the same order. a2 is annotated with the @{unordered}
   annotation.

                  $a1 =              [ string, integer ]
                  $a2 = @{unordered} [ string, integer ]

                                 Figure 37

   The JSON array below does not match a1 but does match a2.

                            [ 24, "Bob Smurd" ]

                                 Figure 38

   Like ordered array specifications, the subordinate components in an
   unordered array specification are evaluated in the order they are
   specified.  The difference is that they need not match an element of
   the array in the same position as given in the array specification.

   Finally, like ordered array specifications, unordered array
   specifications also require that all elements of the array be matched
   by a subordinate component.  If the array has more elements than can
   be matched, the array does not match the array specification.

4.10.  Group Specifications

   Unlike the other type specifications, group specifications have no
   direct tie with JSON syntax.  Group specifications simply group
   together their subordinate components.  Group specifications enclose
   one or more subordinate components with the parenthesis characters.




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   Group specifications and any nesting of group specifications, must
   conform to the allowable set of type specifications of the type
   specifications in which they are contained.  For example, a group
   specification inside of an array specification may not contain a
   member specification since member specifications are not allowed as
   direct subordinates of array specifications (arrays contain values,
   not object members in JSON).  Likewise, a group specification
   referenced inside an object specification must only contain member
   specifications (JSON objects may only contain object members).

   The following is an example of a group specification:

             $the_bradys = [ $parents, $children ]

             $children = ( "Greg", "Marsha", "Bobby", "Jan" )

             $parents = ( "Mike", "Carol" )

                                 Figure 39

   Like the subordinate components of array and object specifications,
   the subordinate components of a group specification are evaluated in
   the order they appear.

4.11.  Ordered and Unordered Groups in Arrays

   Section 4.9.1 specifies that arrays can be evaluated by the order of
   the items in the array or can be evaluated without order.
   Section 4.10 specifies that arrays may have group rules as
   subordinate components.

   The evaluation of a group specification inside an array specification
   inherits the ordering property of the array specification.  If the
   array specification is unordered, then the items of the group
   specification are also considered to be unordered.  And if the array
   specification is ordered, then the items of the group specification
   are also considered to be ordered.

4.12.  Sequence and Choice Combinations in Array, Object, and Group
       Specifications

   Combinations of subordinate components in array, object, and group
   specifications can be specified as either a sequence ("and") or a
   choice ("or").  A sequence is a subordinate component followed by the
   comma character (',') followed by another subordinate component.  A
   choice is a subordinate component followed by a pipe character ('|')
   followed by another subordinate component.




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                            ; sequence ("and")
                            [ "this" , "that" ]

                            ; choice ("or")
                            [ "this" | "that" ]

                                 Figure 40

   Sequence and choice combinations cannot be mixed, and group
   specifications must be used to explicitly declare precedence between
   a sequence and a choice.  Therefore, the following is illegal:

                     [ "this", "that" | "the_other" ]

                                 Figure 41

   The example above should be expressed as:

                   [ "this", ( "that" | "the_other" ) ]

                                 Figure 42

      NOTE: A future specification will clarify the choice ('|')
      operation as inclusive or, exclusive or ("xor") or otherwise.  At
      present readers should assume the choice ('|') operator is an
      inclusive or.  However, for objects and unordered arrays that is
      not ideal, nor is xor.  We are in the process of defining an
      algorithm to "rewrite" choices of rules for use with inclusive or
      which is more suitable for the data model of JSON.

4.13.  Repetition in Array, Object, and Group Specifications

   Evaluation of subordinate components in array, object, and group
   specifications may be succeeded by a repetition expression denoting
   how many times the subordinate component should be evaluated.
   Repetition expressions are specified using a Kleene symbol ('?', '+',
   or '*') or with the '*' symbol succeeded by specific minimum and/or
   maximum values, each being non-negative integers.  Repetition
   expressions may also be appended with a step expression, which is the
   '%' symbol followed by a positive integer.

   When no repetition expression is present, both the minimum and
   maximum are 1.

   A minimum and maximum can be expressed by giving the minimum followed
   by two period characters ('..') followed by the maximum, with either
   the minimum or maximum being optional.  When the minimum is not




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   explicitly specified, it is assumed to be zero.  When the maximum is
   not explicitly specified, it is assumed to be positive infinity.

                      ; exactly 2 octets
                      $word = [ $octet *2 ]
                      $octet =: int8

                      ; 1 to 13 name servers
                      [ $name_servers *1..13 ]
                      $name_servers =: fqdn

                      ; 0 to 99 ethernet addresses
                      { /^eth.*/ : $mac_addr *..99 }
                      $mac_addr =: hex

                      ; four or more bytes
                      [ $octet *4.. ]

                                 Figure 43

   The allowable Kleene operators are the question mark character ('?')
   which specifies zero or one (i.e. optional), the plus character ('+')
   which specifies one or more, and the asterisk character ('*') which
   specifies zero or more.

                  ; age is optional
                  { "name" : string, "age" : integer ? }

                  ; zero or more errors
                  $error_set = ( string * )

                  ; 1 or more integer values
                  [ integer + ]

                                 Figure 44

   A repetition step expression may follow a minimum to maximum
   expression or the zero or more Kleene operator or the one or more
   Kleene operator.

   o  When the repetition step follows a minimum to maximum expression
      or the zero or more Kleene operator ('*'), it specifies that the
      total number of repetitions present in the JSON instance being
      validated minus the minimum repetition value must be a multiple of
      the repetition step (e.g. the total repetitions minus the minimum
      repetition value must be divisible by the step value with a
      remainder of zero).




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   o  When the repetition step follows a one or more Kleene operator
      ('+'), the minimum repetition value is set equal to the repetition
      step value and the total number of repetitions minus the step
      value must be a multiple of the repetition step value.

   The following is an example for repetition steps in repetition
   expressions.

             ; there must be at least 2 name servers
             ; there may be no more than 12 name servers
             ; there must be an even number of name servers
             ; e.g. 2,4,6,8,10,12
             [ $name_servers *2..12%2 ]
             $name_servers =: fqdn

             ; minimum is zero
             ; maximum is 100
             ; must be an even number
             { /^eth.*/ : $mac_addr *..100%2 }
             $mac_addr =: hex

             ; at least 32 octets
             ; must be be in groups of 16
             ; e.g. 32, 48, 64 etc
             [ $octet *32..%16 ]
             $octet =: int8

             ; if there are to be error sets,
             ; their number must be divisible by 4
             ; e.g. 0, 4, 8, 12 etc
             $error_set = ( string *%4 )

             ; Throws of a pair of dice must be divisible by 2
             ; e.g. 2, 4, 6 etc
             $dice_throws = ( 1..6 +%2 )

                                 Figure 45

4.14.  Negating Evaluation

   The evaluation of a rule can be changed with the @{not} annotation.
   With this annotation, a rule that would otherwise match does not, and
   a rule that would not have matched does.








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            ; match anything that isn't the integer 2
            $not_two = [ @{not} 2 ]

            ; error if one of the status values is "fail"
            $status = @{not} @{unordered} [ "fail", string * ]

                                 Figure 46

5.  Directives

   Directives modify the processing of a ruleset.  There are two forms
   of the directive, the single line directive and the multi-line
   directive.

   Single line directives appear on their own line in a ruleset, begin
   with a hash character ('#') and are terminated by the end of the
   line.  They take the following form:

               # directive_name parameter_1 parameter_2 ...

                                 Figure 47

   Multi-line directives also appear on their own lines, but may span
   multiple lines.  They begin with the character sequence "#{" and end
   with "}".  The take the following form:

                        #{ directive_name
                            parameter_1 paramter_2
                            parameter_3
                            ...
                        }

                                 Figure 48

   This specification defines the directives "jcr-version", "ruleset-
   id", and "import", but other directives may be defined.

5.1.  jcr-version

   This directive declares that the ruleset complies with a specific
   version of this standard.  The version is expressed as a major
   integer followed by a period followed by a minor integer.

                             # jcr-version 0.7

                                 Figure 49





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   The major.minor number signifying compliance with this document is
   "0.7".  Upon publication of this specification as an IETF proposed
   standard, it will be "1.0".

                             # jcr-version 1.0

                                 Figure 50

   Ruleset authors are advised to place this directive as the first line
   of a ruleset.

   This directive may have optional extension identifiers following the
   version number.  Each extension identifiers is preceded by the plus
   ('+') character and separated by white space.  The format of
   extension identifiers is specific to the extension, but it is
   recommended that they are terminated by a version number.

            # jcr-version 1.0 +co-constraints-1.2 +jcr-doc-1.0

                                 Figure 51

5.2.  ruleset-id

   This directive identifies a ruleset to rule processors.  It takes the
   form:

                          # ruleset-id identifier

                                 Figure 52

   An identifier can be a URL (e.g. http://example.com/foo), an inverted
   domain name (e.g. com.example.foo) or any other form that conforms to
   the JCR ABNF syntax that a ruleset author deems appropriate.  To a
   JCR processor the identifier is treated as an opaque, case-sensitive
   string.

5.3.  import

   The import directive specifies that another ruleset is to have its
   rules evaluated in addition to the ruleset where the directive
   appears.

   The following is an example:

              # import http://example.com/rfc9999 as rfc9999

                                 Figure 53




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   The rule names of the ruleset to be imported may be referenced by
   prepending the alias followed by a period character ('.') followed by
   the rule name (i.e. "alias.name").  To continue the example above, if
   the ruleset at http://example.com/rfc9999 were to have a rule named
   'encoding', rules in the ruleset importing it can refer to that rule
   as 'rfc9999.encoding'.

6.  Tips and Tricks

6.1.  Any Member with Any Value

   Because member names may be specified with regular expressions, it is
   possible to construct a member rule that matches any member name.  As
   an example, the following defines an object with a member with any
   name that has a value that is a string:

                              { // : string }

                                 Figure 54

   The JSON below matches the above rule.

                             { "foo" : "bar" }

                                 Figure 55

   Likewise, the JSON below also matches the same rule.

                            { "fuzz" : "bazz" }

                                 Figure 56

   Constructing an object with a member of any name with any type would
   therefore take the form:

                               { // : any }

                                 Figure 57

   The above rule matches not only the two JSON objects above, but the
   JSON object below.

                             { "fuzz" : 1234 }

                                 Figure 58






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6.2.  Lists of Values

   Group specifications may be used to create enumerated lists of
   primitive data types, because primitive specifications may contain a
   group specification, which may have multiple primitive
   specifications.  Because a primitive specification must resolve to a
   single data type, the group specification must only contain choice
   combinations.

   Consider the following examples:

                ; either an IPv4 or IPv6 adress
                $address =: ( ipv4 | ipv6 )

                ; allowable fruits
                $fruits =: ( "apple" | "banana" | "pear" )

                                 Figure 59

6.3.  Groups in Arrays

   Groups may be a subordinate component of array specifications:

                       [ ( ipv4 | ipv6 ), integer ]

                                 Figure 60

   Unlike primitive specifications, subordinate group specifications in
   array specifications may have sequence combinations and contain any
   type specification.

           ; a group in an array
           [ ( $first_name, $middle_name ?, $last_name ), $age ]

           ; a group referenced from an array
           [ $name, $age ]
           $name = ( $first_name, $middle_name ?, $last_name )

           $first_name =: string
           $middle_name =: string
           $last_name =: string
           $age =: 0..

                                 Figure 61







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6.4.  Groups in Objects

   Groups may be a subordinate component of object specifications:
   Subordinate group specifications in object specifications may have
   sequence combinations but must only contain member specifications.

               ; a group in an object
               { ( $title, $date, $author ), $paragraph + }

               ; a group referenced from an object
               { $front_matter, $paragraph + }
               $front_matter = ( $title, $date, $author )

               $title = "title" : string
               $date = "date" : date
               $author = "author" : [ string * ]
               $paragraph = /p[0-9]*/ : string

                                 Figure 62

      NOTE: A future specification will clarify the choice ('|')
      operation as inclusive or, exclusive or ("xor") or otherwise.  At
      present readers should assume the choice ('|') operator is an
      inclusive or.  We are in the process of defining an algorithm to
      "rewrite" choices of rules for use with inclusive or which is more
      suitable for the data model of JSON.  Such a change will impact
      the guidance given below.

   When using groups to use both sequences and choices of member
   specifications, consideration must be given to the processing of
   object specifications where by unmatched member specifications are
   ignored (see Figure 23).

   A casual reading of this rule might lead a reader to believe that the
   JSON object in Figure 64 would not match, however it does because the
   extra member (either "foo" or "baz") is not matched but is ignored.

            { "bar":string, ( "foo":integer | "baz":string ) }

                                 Figure 63

                { "bar":"thing", "foo":2, "baz": "thingy" }

                                 Figure 64

   The rule in Figure 63 must be modified to either match all extra
   rules, as in Figure 65, or the logic of the rules must be rewritten




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   to explicitly negate the presence of the unwanted members, as in
   Figure 66.

    { "bar":string, ( "foo":integer | "baz":string ), @{not} //:any + }

                                 Figure 65

               { "bar":string,
                 ( ( "foo":integer , @{not} "baz":string ) |
                   ( "baz":string , @{not} "foo":integer )
               ) }

                                 Figure 66

6.5.  Group Rules as Macros

   The syntax for group specifications accommodates one ore more
   subordinate components and a repetition expression for each.  Other
   than grouping multiple rules, a group specification can be used as a
   macro definition for a single rule.

                  $paragraphs = ( /p[0-9]*/ : string + )

                                 Figure 67

6.6.  Object Mixins

   Group rules can be used to create object mixins, a pattern for
   writing data models similar in style to object derivation in some
   programming languages.  In the example in below, both obj1 and obj2
   have a members "foo" and "fob" with obj1 having the additional member
   "bar" and obj2 having the additional member "baz".

              $mixin_group = ( "foo" : integer, "fob" : uri )

              $obj1 = { $mixin_group, "bar" : string }

              $obj2 = { $mixin_group, "baz" : string }

                                 Figure 68

6.7.  Subordinate Dependencies

   In object and array specifications, there may be situations in which
   it is necessary to condition the existence of a subordinate component
   on the existence of a sibling subordinate component.  In other words,
   example_two should only be evaluated if example_one evaluates
   positively.  Or put another way, a member of an object or an item of



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   an array may be present only on the condition that another member or
   item is present.

   In the following example, the referrer_uri member can only be present
   if the location_uri member is present.

                  ; $referrer_uri can only be present if
                  ; $location_uri is present
                  { ( $location_uri, $referrer_uri? )? }

                  $location_uri = "locationURI" : uri
                  $referrer_uri = "referrerURI" : uri

                                 Figure 69

7.  Implementation Status

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7492] .
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7492] , "this will allow reviewers and working
   groups to assign due consideration to documents that have the benefit
   of running code, which may serve as evidence of valuable
   experimentation and feedback that have made the implemented protocols
   more mature.  It is up to the individual working groups to use this
   information as they see fit".

7.1.  JCR Validator

   The JCR Validator, written in Ruby, currently implements all portions
   of this specification, and has been used extensively to prototype
   various aspects of JCR under consideration.  It's development has
   gone hand-in-hand with this specification.

   This software is primarily produced by the American Registry for
   Internet Numbers (ARIN) and freely distributable under the ISC
   license.




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   Source code for this software is available on GitHub at
   <https://github.com/arineng/jcrvalidator>.  This software is also
   easily obtained as a Ruby Gem through the Ruby Gem system.

7.2.  Codalogic JCR Parser

   The Codalogic JCR Parser is a C++ implementation of a JCR parsing
   engine, and is a work in progress.  It is targeted for the Windows
   platform.

   This software is produced by Codalogic Ltd and freely distributable
   under the Gnu LGPL v3 license.

   Source code is availabe on GitHub at <https://github.com/codalogic/
   cl-jcr-parser>.

7.3.  JCR Java

   JCR Java is a work in progress and currently only implements the
   parsing of JCR rulesets according to the ABNF using a custom parsing
   framework.

   This software is produced by the American Registry for Internet
   Numbers (ARIN) and freely distributable under the MIT license.

   Source code is available on BitBucket at
   <https://bitbucket.org/anewton_1998/jcr_java>.

8.  ABNF Syntax

   The following ABNF describes the syntax for JSON Content Rules.  A
   text file containing these ABNF rules can be downloaded from
   [JCR_ABNF].

 jcr              = *( sp-cmt / directive / root-rule / rule )

 sp-cmt           = spaces / comment
 spaces           = 1*( WSP / CR / LF )
 DSPs             = ; Directive spaces
                    1*WSP /     ; When in one-line directive
                    1*sp-cmt   ; When in muti-line directive
 comment          = ";" *comment-char comment-end-char
 comment-char     = HTAB / %x20-10FFFF
                    ; Any char other than CR / LF
 comment-end-char = CR / LF

 directive        = "#" (one-line-directive / multi-line-directive)
 one-line-directive = [ DSPs ]



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                    (directive-def / one-line-tbd-directive-d)
                    *WSP eol
 multi-line-directive = "{" *sp-cmt
                    ( directive-def /
                    multi-line-tbd-directive-d )
                    *sp-cmt "}"
 directive-def    = jcr-version-d / ruleset-id-d / import-d
 jcr-version-d    = jcr-version-kw DSPs major-version
                    "." minor-version
                    *( DSPs "+" [ DSPs ] extension-id )
 major-version    = non-neg-integer
 minor-version    = non-neg-integer
 extension-id     = ALPHA *not-space
 ruleset-id-d     = ruleset-id-kw DSPs ruleset-id
 import-d         = import-kw DSPs ruleset-id
                    [ DSPs as-kw DSPs ruleset-id-alias ]
 ruleset-id       = ALPHA *not-space
 not-space        = %x21-10FFFF
 ruleset-id-alias = name
 one-line-tbd-directive-d = directive-name
                    [ WSP one-line-directive-parameters ]
 directive-name   = name
 one-line-directive-parameters = *not-eol
 not-eol          = HTAB / %x20-10FFFF
 eol              = CR / LF
 multi-line-tbd-directive-d = directive-name
                    [ 1*sp-cmt multi-line-directive-parameters ]
 multi-line-directive-parameters = multi-line-parameters
 multi-line-parameters = *(comment / q-string / regex /
                    not-multi-line-special)
 not-multi-line-special = spaces / %x21 / %x23-2E / %x30-3A /
                    %x3C-7C / %x7E-10FFFF ; not ", /, ; or }

 root-rule        = value-rule / group-rule

 rule             = annotations "$" rule-name *sp-cmt
                    "=" *sp-cmt rule-def

 rule-name        = name
 target-rule-name = annotations "$"
                    [ ruleset-id-alias "." ]
                    rule-name
 name             = ALPHA *( ALPHA / DIGIT / "-" / "-" )

 rule-def         = member-rule / type-designator rule-def-type-rule /
                    array-rule / object-rule / group-rule /
                    target-rule-name
 type-designator  = type-kw 1*sp-cmt / ":" *sp-cmt



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 rule-def-type-rule = value-rule / type-choice
 value-rule       = primitive-rule / array-rule / object-rule
 member-rule      = annotations
                    member-name-spec *sp-cmt ":" *sp-cmt type-rule
 member-name-spec = regex / q-string
 type-rule        = value-rule / type-choice / target-rule-name
 type-choice      = annotations "(" type-choice-items
                    *( choice-combiner type-choice-items ) ")"
 explicit-type-choice = type-designator type-choice
 type-choice-items = *sp-cmt ( type-choice / type-rule ) *sp-cmt

 annotations      = *( "@{" *sp-cmt annotation-set *sp-cmt "}"
                    *sp-cmt )
 annotation-set   = not-annotation / unordered-annotation /
                    root-annotation / tbd-annotation
 not-annotation   = not-kw
 unordered-annotation = unordered-kw
 root-annotation  = root-kw
 tbd-annotation   = annotation-name [ spaces annotation-parameters ]
 annotation-name  = name
 annotation-parameters = multi-line-parameters

 primitive-rule   = annotations primitive-def
 primitive-def    = string-type / string-range / string-value /
                    null-type / boolean-type / true-value /
                    false-value / double-type / float-type /
                    float-range / float-value /
                    integer-type / integer-range / integer-value /
                    sized-int-type / sized-uint-type / ipv4-type /
                    ipv6-type / ipaddr-type / fqdn-type / idn-type /
                    uri-type / phone-type / email-type /
                    datetime-type / date-type / time-type /
                    hex-type / base32hex-type / base32-type /
                    base64url-type / base64-type / any
 null-type        = null-kw
 boolean-type     = boolean-kw
 true-value       = true-kw
 false-value      = false-kw
 string-type      = string-kw
 string-value     = q-string
 string-range     = regex
 double-type      = double-kw
 float-type       = float-kw
 float-range      = float-min ".." [ float-max ] / ".." float-max
 float-min        = float
 float-max        = float
 float-value      = float
 integer-type     = integer-kw



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 integer-range    = integer-min ".." [ integer-max ] /
                    ".." integer-max
 integer-min      = integer
 integer-max      = integer
 integer-value    = integer
 sized-int-type   = int-kw pos-integer
 sized-uint-type  = uint-kw pos-integer
 ipv4-type        = ipv4-kw
 ipv6-type        = ipv6-kw
 ipaddr-type      = ipaddr-kw
 fqdn-type        = fqdn-kw
 idn-type         = idn-kw
 uri-type         = uri-kw [ ".." uri-scheme ]
 phone-type       = phone-kw
 email-type       = email-kw
 datetime-type    = datetime-kw
 date-type        = date-kw
 time-type        = time-kw
 hex-type         = hex-kw
 base32hex-type   = base32hex-kw
 base32-type      = base32-kw
 base64url-type   = base64url-kw
 base64-type      = base64-kw
 any              = any-kw

 object-rule      = annotations "{" *sp-cmt
                    [ object-items *sp-cmt ] "}"
 object-items     = object-item [ 1*( sequence-combiner object-item ) /
                    1*( choice-combiner object-item ) ]
 object-item      = object-item-types *sp-cmt [ repetition *sp-cmt ]
 object-item-types = object-group / member-rule / target-rule-name
 object-group     = annotations "(" *sp-cmt [ object-items *sp-cmt ] ")"

 array-rule       = annotations "[" *sp-cmt [ array-items *sp-cmt ] "]"
 array-items      = array-item [ 1*( sequence-combiner array-item ) /
                    1*( choice-combiner array-item ) ]
 array-item       = array-item-types *sp-cmt [ repetition *sp-cmt ]
 array-item-types = array-group / type-rule / explicit-type-choice
 array-group      = annotations "(" *sp-cmt [ array-items *sp-cmt ] ")"

 group-rule       = annotations "(" *sp-cmt [ group-items *sp-cmt ] ")"
 group-items      = group-item [ 1*( sequence-combiner group-item ) /
                    1*( choice-combiner group-item ) ]
 group-item       = group-item-types *sp-cmt [ repetition *sp-cmt ]
 group-item-types = group-group / member-rule /
                    type-rule / explicit-type-choice
 group-group      = group-rule




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 sequence-combiner = "," *sp-cmt
 choice-combiner  = "|" *sp-cmt

 repetition       = optional / one-or-more /
                    repetition-range / zero-or-more
 optional         = "?"
 one-or-more      = "+" [ repetition-step ]
 zero-or-more     = "*" [ repetition-step ]
 repetition-range = "*" *sp-cmt (
                    min-max-repetition / min-repetition /
                    max-repetition / specific-repetition )
 min-max-repetition = min-repeat ".." max-repeat
                    [ repetition-step ]
 min-repetition   = min-repeat ".." [ repetition-step ]
 max-repetition   = ".."  max-repeat [ repetition-step ]
 min-repeat       = non-neg-integer
 max-repeat       = non-neg-integer
 specific-repetition = non-neg-integer
 repetition-step  = "%" step-size
 step-size        = non-neg-integer

 integer          = "0" / ["-"] pos-integer
 non-neg-integer  = "0" / pos-integer
 pos-integer      = digit1-9 *DIGIT

 float            = [ minus ] int frac [ exp ]
                    ; From RFC 7159 except 'frac' required
 minus            = %x2D                          ; -
 plus             = %x2B                          ; +
 int              = zero / ( digit1-9 *DIGIT )
 digit1-9         = %x31-39                       ; 1-9
 frac             = decimal-point 1*DIGIT
 decimal-point    = %x2E                          ; .
 exp              = e [ minus / plus ] 1*DIGIT
 e                = %x65 / %x45                   ; e E
 zero             = %x30                          ; 0

 q-string         = quotation-mark *char quotation-mark
                    ; From RFC 7159
 char             = unescaped /
                    escape (
                    %x22 /          ; "    quotation mark  U+0022
                    %x5C /          ; \    reverse solidus U+005C
                    %x2F /          ; /    solidus         U+002F
                    %x62 /          ; b    backspace       U+0008
                    %x66 /          ; f    form feed       U+000C
                    %x6E /          ; n    line feed       U+000A
                    %x72 /          ; r    carriage return U+000D



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                    %x74 /          ; t    tab             U+0009
                    %x75 4HEXDIG )  ; uXXXX                U+XXXX
 escape           = %x5C              ; \
 quotation-mark   = %x22      ; "
 unescaped        = %x20-21 / %x23-5B / %x5D-10FFFF

 regex            = "/" *( escape "/" / not-slash ) "/"
                    [ regex-modifiers ]
 not-slash        = HTAB / CR / LF / %x20-2E / %x30-10FFFF
                    ; Any char except "/"
 regex-modifiers  = *( "i" / "s" / "x" )

 uri-scheme       = 1*ALPHA

 ;; Keywords
 any-kw           = %x61.6E.79                      ; "any"
 as-kw            = %x61.73                         ; "as"
 base32-kw        = %x62.61.73.65.33.32             ; "base32"
 base32hex-kw     = %x62.61.73.65.33.32.68.65.78    ; "base32hex"
 base64-kw        = %x62.61.73.65.36.34             ; "base64"
 base64url-kw     = %x62.61.73.65.36.34.75.72.6C    ; "base64url"
 boolean-kw       = %x62.6F.6F.6C.65.61.6E          ; "boolean"
 date-kw          = %x64.61.74.65                   ; "date"
 datetime-kw      = %x64.61.74.65.74.69.6D.65       ; "datetime"
 double-kw        = %x64.6F.75.62.6C.65             ; "double"
 email-kw         = %x65.6D.61.69.6C                ; "email"
 false-kw         = %x66.61.6C.73.65                ; "false"
 float-kw         = %x66.6C.6F.61.74                ; "float"
 fqdn-kw          = %x66.71.64.6E                   ; "fqdn"
 hex-kw           = %x68.65.78                      ; "hex"
 idn-kw           = %x69.64.6E                      ; "idn"
 import-kw        = %x69.6D.70.6F.72.74             ; "import"
 int-kw           = %x69.6E.74                      ; "int"
 integer-kw       = %x69.6E.74.65.67.65.72          ; "integer"
 ipaddr-kw        = %x69.70.61.64.64.72             ; "ipaddr"
 ipv4-kw          = %x69.70.76.34                   ; "ipv4"
 ipv6-kw          = %x69.70.76.36                   ; "ipv6"
 jcr-version-kw   = %x6A.63.72.2D.76.65.72.73.69.6F.6E ; "jcr-version"
 not-kw           = %x6E.6F.74                      ; "not"
 null-kw          = %x6E.75.6C.6C                   ; "null"
 phone-kw         = %x70.68.6F.6E.65                ; "phone"
 root-kw          = %x72.6F.6F.74                   ; "root"
 ruleset-id-kw    = %x72.75.6C.65.73.65.74.2D.69.64 ; "ruleset-id"
 string-kw        = %x73.74.72.69.6E.67             ; "string"
 time-kw          = %x74.69.6D.65                   ; "time"
 true-kw          = %x74.72.75.65                   ; "true"
 type-kw          = %x74.79.70.65                   ; "type"
 uint-kw          = %x75.69.6E.74                   ; "uint"



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 unordered-kw     = %x75.6E.6F.72.64.65.72.65.64    ; "unordered"
 uri-kw           = %x75.72.69                      ; "uri"

 ;; Referenced RFC 5234 Core Rules
 ALPHA            = %x41-5A / %x61-7A   ; A-Z / a-z
 CR               = %x0D         ; carriage return
 DIGIT            = %x30-39      ; 0-9
 HEXDIG           = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
 HTAB             = %x09         ; horizontal tab
 LF               = %x0A         ; linefeed
 SP               = %x20         ; space
 WSP              = SP / HTAB    ; white space

                  Figure 70: ABNF for JSON Content Rules

9.  Acknowledgements

   John Cowan, Andrew Biggs, Paul Kyzivat and Paul Jones provided
   feedback and suggestions which led to many changes in the syntax.

10.  References

10.1.  Normative References

   [JCR_ABNF]
              Newton, A. and P. Cordell, "ABNF for JSON Content Rules",
              <https://raw.githubusercontent.com/arineng/jcr/master/
              jcr-abnf.txt>.

   [RFC1166]  Kirkpatrick, S., Stahl, M., and M. Recker, "Internet
              numbers", RFC 1166, DOI 10.17487/RFC1166, July 1990,
              <https://www.rfc-editor.org/info/rfc1166>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, DOI 10.17487/RFC4234,
              October 2005, <https://www.rfc-editor.org/info/rfc4234>.






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   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <https://www.rfc-editor.org/info/rfc5952>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

10.2.  Infomative References

   [I-D.cordell-jcr-co-constraints]
              Cordell, P. and A. Newton, "Co-Constraints for JSON
              Content Rules", draft-cordell-jcr-co-constraints-00 (work
              in progress), March 2016.

   [RFC7492]  Bhatia, M., Zhang, D., and M. Jethanandani, "Analysis of
              Bidirectional Forwarding Detection (BFD) Security
              According to the Keying and Authentication for Routing
              Protocols (KARP) Design Guidelines", RFC 7492,
              DOI 10.17487/RFC7492, March 2015,
              <https://www.rfc-editor.org/info/rfc7492>.

10.3.  URIs

   [1] https://github.com/arineng/jcr/tree/master/figs

Appendix A.  Co-Constraints

   This specification defines a small set of annotations and directives
   for JCR, yet the syntax is extensible allowing for other annotations
   and directives.  [I-D.cordell-jcr-co-constraints] ("Co-Constraints
   for JCR") defines further annotations and directives which define
   more detailed constraints on JSON messages, including co-constraints
   (constraining parts of JSON message based on another part of a JSON
   message).







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Appendix B.  Testing Against JSON Content Rules

   One aspect of JCR that differentiates it from other format schema
   languages are the mechanisms helpful to developers for taking a
   formal specification, such as that found in an RFC, and evolving it
   into unit tests, which are essential to producing quality protocol
   implementations.

B.1.  Locally Overriding Rules

   As mentioned in the introduction, one tool for testing would be the
   ability to locally override named rules.  As an example, consider the
   following rule which defines an array of strings.

                         $statuses = [ string * ]

                                 Figure 71

   Consider the specification where this rule is found does not define
   the values but references an extensible list of possible values
   updated independently of the specification, such as in an IANA
   registry.

   If a software developer desired to test a specific situation in which
   the array must at least contain the status "accepted", the rules from
   the specification could be used and the statuses rule could be
   explicitly overridden locally as:

   This rule will evaluate positively with the JSON in Figure 73

             $statuses = @{unordered} [ "accepted", string * ]

                                 Figure 72

                 [ "submitted", "validated", "accepted" ]

                                 Figure 73

   Alternatively, the developer may need to ensure that the status
   "denied" should not be present in the array:

   This rule will fail to evaluate the JSON in Figure 75 thus signaling
   a problem.

         $statuses = @{unordered} @{not} [ "denied" + , string * ]

                                 Figure 74




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                  [ "submitted", "validated", "denied" ]

                                 Figure 75

B.2.  Rule Callbacks

   In many testing scenarios, the evaluation of rules may become more
   complex than that which can be expressed in JCR, sometimes involving
   variables and interdependencies which can only be expressed in a
   programming language.

   A JCR processor may provide a mechanism for the execution of local
   functions or methods based on the name of a rule being evaluated.
   Such a mechanism could pass to the function the data to be evaluated,
   and that function could return to the processor the result of
   evaluating the data in the function.

Appendix C.  Changes from -07 and -08

   This revision of the document makes no substantive changes to any
   parts of the specification.  Some of the ABNF has been updated to
   more correctly allow group rules, and other small change have been
   made to the ABNF to make it simpler.

Authors' Addresses

   Andrew Lee Newton
   American Registry for Internet Numbers
   PO Box 232290
   Centreville, VA  20120
   US

   Email: andy@arin.net
   URI:   http://www.arin.net


   Pete Cordell
   Codalogic
   PO Box 30
   Ipswich  IP5 2WY
   UK

   Email: pete.cordell@codalogic.com
   URI:   http://www.codalogic.com







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