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Versions: 00 01 02 03 04 05 06 07 08 09                                 
Network Working Group                                          A. Newton
Internet-Draft                                                      ARIN
Intended status: Standards Track                        December 2, 2014
Expires: June 5, 2015


              A Language for Rules Describing JSON Content
                   draft-newton-json-content-rules-04

Abstract

   This document describes a language useful for describing the expected
   content of JSON structures found in JSON-using protocols.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 June 5, 2015.

Copyright Notice

   Copyright (c) 2014 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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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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1.  Introduction

   The goal of this document is to provide a way to specify the expected
   content of data expressed in JSON [RFC4627] format.  That is, the
   primary purpose of this document is to specify a means for one person
   to communicate with another person the expected nature of a JSON data
   structure in a method more concise and unambiguous than prose.  The
   programmatic validation of a JSON data structure against content
   rules is a lesser goal of this document, though such a practice is
   useful in both the writing of specifications and the communications
   of programs.

   Unlike JSON Schema, this language is not JSON though the syntax
   described here is "JSON-like" (a comparison with JSON Schema can be
   found in Appendix A and a "real world" example can be found in
   Appendix B).  A specialized syntax is used to reduce the tedium in
   reading and writing rules as the complexity describing allowable
   content is often more involved than most of the actual content.
   Figure 2 is an example of this language describing the JSON of
   Figure 1.

   Example JSON lifted from RFC 4627

   [
       {
          "precision": "zip",
          "Latitude":  37.7668,
          "Longitude": -122.3959,
          "Address":   "",
          "City":      "SAN FRANCISCO",
          "State":     "CA",
          "Zip":       "94107",
          "Country":   "US"
       },
       {
          "precision": "zip",
          "Latitude":  37.371991,
          "Longitude": -122.026020,
          "Address":   "",
          "City":      "SUNNYVALE",
          "State":     "CA",
          "Zip":       "94085",
          "Country":   "US"
       }
   ]

                                 Figure 1




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   Rules describing Figure 1

   root [
       2*2{
           "precision" : string,
           "Latitude" : float,
           "Longitude" : float,
           "Address" : string,
           "City" : string,
           "State" : string,
           "Zip" : string,
           "Country" : string
       }
   ]

                                 Figure 2

   The JSON Content Rules are of five types:

   o  value rules

   o  member rules

   o  array rules

   o  object rules

   o  group rules

   Each rule has two components, a rule name and a rule definition.
   Anywhere in a rule definition where a rule name is allowed, another
   rule definition may be used.

   This is an example of a value rule:

      v1 : integer 0..3

   It specifies a rule named "v1" that has a definition of ": integer
   0..3" (value rule definitions begin with a ':' character).  This
   defines values of type "v1" to be integers in the range 0 to 3
   (minimum value of 0, maximum value of 3).  Value rules can define the
   limits of JSON values, such as stating that numbers must fall into a
   certain range or that strings must be formatted according to certain
   patterns or standards (i.e.  URIs, phone numbers, etc...).

   Member rules specify JSON object members.  The following example
   member rule states that the rule's name is 'm1' with a value defined
   by the 'v1' value rule:



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      m1 "m1name" v1

   Since rule names can be substituted by rule definitions, this member
   rule can also be written as follows (to define a member rule named m1
   for JSON member "m1name" that has a value that is an integer between
   0 and 3):

      m1 "m1name" : integer 0..3

   Object rules are composed of member rules, since JSON objects are
   composed of members.  Object rules can specify members that are
   mandatory, optional, and even choices between members.  In this
   example, the rule 'o1' defines an object that must contain a member
   as defined by member rule 'm1' and optionally a member defined by the
   rule 'm2':

      o1 { m1, ?m2 }

   Array rules are composed of value, object, and other array rules.
   Like object rules, array rules can specify the cardinality of the
   contents of an array.  The following array rule defines an array that
   must contain value rule 'v1' and zero or more objects as defined by
   rule 'o1':

      a1 [ v1, *o1 ]

   Finally, group rules designate a collection of rules.

   Putting it all together, Figure 4 describes the JSON in Figure 3.

   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 3




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   Rules describing Figure 3

   width_v : integer 0..1280
   height_v : integer 0..1024

   width "Width" width_v
   height "Height" height_v

   thumbnail "Thumbnail" {
       width, height, "Url" : uri
   }

   image "Image" {
       width, height, "Title" : string,
       thumbnail, "IDs" [ *: integer ]
   }

   root { image }

                                 Figure 4

   The rules from Figure 4 can be written more compactly (see Figure 5).

   Compact rules describing Figure 3

   width "Width" : integer 0..1280
   height "Height" : integer 0..1024

   root {
       "Image" {
           width, height, "Title" :string,
           "Thumbnail" { width, height, "Url" :uri },
           "IDs" [ *:integer ]
       }
   }

                                 Figure 5

2.  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.

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





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3.  Rules

   Rules are composed of two parts, a rule name and a rule definition:

      <rule name> <rule definition>

   Rule names allow a rule to be referenced easily by a name.  A rule
   definition describes the validity upon which the content is to be
   judged.  With the exception of value rules, rule definitions refer to
   other rules using the rule names of other rules of appropriate type.

   A rule definition may embed another rule definition where a rule name
   is allowed.  In other words, some rules are named and some are
   anonymous.  Named rules start with a rule name and have a rule
   definition.  Anonymous rules are rule definitions embedded in the
   definitions of other rules.

   The type of rule to use in a rule definition, either directly or by
   reference of a name, depends on the type of rule being defined and
   fall along the structure of allowable JSON grammar:

   o  Since a member of a JSON object can contain a "primitive value",
      an array, or an object, member rules can be composed of value
      rules, array rules, and object rules.

   o  JSON objects are composed of members, so object rules can only be
      composed of member rules.

   o  Finally, as JSON arrays may contain other arrays, objects, and
      values, array rules may be composed of value rules, object rules,
      and array rules.

   A fifth rule type, group rules, exist to help reference a collection
   of rules.  Object rules and array rules may contain group rules so
   long as the groups contain only the appropriate type of rule of the
   containing rule.

   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 ('_').  Rule names must
   not be used more than once and are case sensitive.

3.1.  Value Rules

   Value rules define content for JSON values.  JSON allows values to be
   objects, arrays, numbers, booleans, strings, and null.  Arrays and
   objects are handled by the array and object rules, and the value
   rules define the rest.



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3.1.1.  Numbers, Booleans and Null

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

      rule_name : boolean

      rule_name : null

   Rules for numbers can specify the number as either an integer or
   floating point number and may specify a range:

      rule_name : integer n..m

      rule_name : float n..m

   where n is the minimum allowable value of the number and m is the
   maximum allowable value of the number.  The range doesn't have to be
   given, but if it is given either the minimum, maximum, or both are
   required.  If the minimum is not given then the minimum is considered
   to be the minimum number value possible to represent in JSON.
   Likewise, if the maximum is not given then the maximum is considered
   to be the maximum number value possible to represent in JSON.

3.1.2.  Strings

   String values may be specified generically as:

      rule_name : string

   However, the content of strings can be narrowed in the following
   ways:

   Regular Expression:   A rule can state that a string must match a
      regular expression by giving the regular expression after the
      string literal:

         rule_name : string /regex/

   URIs and URI templates:   A rule can state that a string must be a
      URI [RFC3986]:

         rule_name : uri

      URIs may be further scoped to a specific URI pattern by prepending
      a URI template [RFC6570]:

         rule_name : uri http://{stuff}



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         rule_name : uri http://{authority}/{thing1}?q={thing2}

      When using URI templates, the variable names are ignored for
      pattern matching, but the should be provided for construction of a
      valid URI template.  Providing the variable names also aids in the
      description of what is to be matched.

   IP Addresses:   Narrowing the content of strings down to IP addresses
      can be done with either the 'ip4' (see [RFC1166]) or 'ip6' (see
      [RFC5952]) literals:

         rule_name : ip4

         rule_name : ip6

   Domain Names:   Fully qualified A-label and U-label domain names can
      be specified with the 'fqdn' and 'idn' literals:

         rule_name : fqdn

         rule_name : idn

   Dates and Times:   Dates and times are specified using the ABNF rules
      from RFC 3339 [RFC3339] as literals:

         rule_name : date-time

         rule_name : full-date

         rule_name : full-time

   Email Addresses:   A string can be scoped to the syntax of email
      addresses using the literal 'email':

         rule_name : email

      Email addresses must conform to the syntax of RFC 5322 [RFC5322].

   Phone Numbers:   Strings conforming to E.123 phone number format can
      be specified as follows:

         rule_name : phone

   Base 64:   Strings containing base 64 data, as described by RFC 4648
      [RFC4648], can be specified as follows:

         rule_name : base64




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3.1.3.  Enumerations

   Enumerations allow a value to be one of the items in an enumerated
   list of possible values.  They take the following form:

      rule_name : < "item1" "item2" "item3" >

   Items in the enumerated list may be quoted strings, integer or
   floating point numbers, or the literals 'true', 'false' or 'null'.
   The types of the items may be mixed, as the following example
   demonstrations:

      truthy : < 1 true "yes" "Y" >

3.2.  Member Rules

   Member rules have the simplest syntax of all the rules and define
   members of JSON objects.  Member rules follow the format:

      rule_name "member_name" target_rule_name

   where rule_name is the name of the rule being defined, member_name
   (in quotes) is the name of the JSON object member, and
   target_rule_name is a reference to a value rule, array rule, or
   object rule specifying the allowable content of the JSON object
   member.

   Since rule names in rule definitions may be replaced by rule
   definitions, member rules may also be written in this form:

      rule_name "member_rule" target_rule_definition

   The following is an example:

      location_uri "locationURI" : uri

3.3.  Object Rules

   Object rules define the allowable members of a JSON object.  Their
   rule definitions are composed of member rules and group rules.  They
   take the following form:

      rule_name { member_rule_1, member_rule_2 }

   The following rule example defines an object composed of two member
   rules:

      response { location_uri, status_code }



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   Given that where a rule name is found a rule definition of the
   appropriate type may be used, the above example might also be
   written:

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

   Rules given in the rule definition of an object rule do not imply
   order.  Given the example object rule above both

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

   and

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

   are JSON objects that match the rule.

   Member rules or member rule definitions may not be repeated in the
   rule definition of an object rule.  However, a member of an object
   can be marked as optional if the member rule defining it is preceded
   by the question mark ('?') character.  In the following example, the
   location_uri member is optional while the status_code member is
   required to be in the defined object:

      response { ?location_uri, status_code }

   An object rule can also define the choice between members by placing
   the forward slash ('/') character between two member rules.  In the
   following example, the object being defined can have either a
   location_uri member or content_type member and must have a
   status_code member:

      response { location_uri / content_type, status_code }

3.4.  Array Rules

   Array rules define the allowable content of JSON arrays.  Their rule
   definitions are composed of value rules, object rules, group rules,
   and other array rules and have the following form:

      rulename [ target_rule_name_1, target_rule_name_2 ]

   The following example defines an array where the first element is
   defined by the width_value rule and the second element is defined by
   the height_value rule:

      size [ width_value, height_value ]




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   Unlike object rules, order is implied by the array rule definition.
   That is, the first rule referenced or defined within an array rule
   specifies that the first element of the array will match that rule,
   the second rule given with the array rule specifies that the second
   element of the array will match that rule, and so on.

   Take for example the following array rule definition:

      person [ : string, : integer ]

   This JSON array matches the above rule:

      [ "Bob Smurd", 24 ]

   while this one does not:

      [ 24, "Bob Smurd" ]

   As with object rules, the forward slash character ('/') can be used
   to indicate a choice between two elements.  Take for example the
   following rules:

      name_value : string

      age_value : integer

      birthdate_value : date-time

      person [ name_value, age_value / birthdate_vale ]

   which would validate

      [ "Bob Smurd", 24 ]

   or

      [ "Bob Smurd", "1988-04-12T23:20:50.52Z" ]

   Repetition of array values may also be specified by preceding a rule
   with an asterisk ('*') character surrounded by the lower bound and
   upper bound of the repetition (e.g. "0*1").  The following rules
   define an array that has between one and three strings:

      child_value : string

      children [ 1*3 child_value ]





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   Both the lower bound and the upper bound are optional.  If lower
   bound is not given then it is assumed to be zero.  If the upper bound
   is not given then it is assumed to be infinity.  The following
   example defines an array with an infinite number of child_value
   defined strings:

      children [ * child_value ]

3.5.  Group Rules

   Unlike the other types of rules, group rules have no direct tie with
   JSON syntax.  Group rules simply group together other rules.  They
   take the form:

      rule_name ( target_rule_1, target_rule_2 )

   Group rule definitions and any nesting of group rule definitions,
   must conform to the allowable set of rules of the rule containing
   them.  A group rule referenced inside of an array rule may not
   contain a member rule since member rules are not allowed in array
   rules directly.  Likewise, a group rule referenced inside an object
   rule must only contain member rules, and once group rules used in an
   object rule are fully dereferenced there must be no duplicate member
   rules as member rules in object rules are required to be unique.

   Take for example the following rules:

      child_1 "first_child" : string

      child_2 "second_child" : string

      child_3 "third_child" : string

      child_4 "fourth_child" : string

      first_two_children ( child_1, child_2 )

      second_two_children ( child_3, child_4 )

      the_children { first_two_children, second_two_children }

   These rules describe a JSON object that might look like this:

      { "first_child":"greg", "second_child":"marsha",
      "third_child":"bobby", "fourth_child":"jan" }

   Groups can also be used with the choice syntax in member rules.  Here
   the object can either have first_two_children or second_two_children:



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      the_children { first_two_children / second_two_children }

   and here the object can have second_two_children only if
   first_two_children are given:

      the_children { first_two_children & second_two_children }

   Group rules can be used to create object mixins.  In the example in
   Figure 6, 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 6

   Group rules used in the definition of object rules may be preceded by
   the '?' character, just as member rules in the definitions of object
   rules, signifying that the group is optional.

      response { ?( location_uri, referrer_uri ) }

   The '?' character may also preceed a rule of the group definition to
   indicate that the rule is optional if the group rule is contained by
   an object rule.  Therefore, group rules can be used to create member
   dependencies.  This object rule defines that referrer_uri can be
   present if location_uri is present.

      response { ?( location_uri, ?referrer_uri ) }

   When group rules are used in the definition of an array rule, they
   may be preceded by the repetition syntax of elements of an array
   definition, and may preceed a rule of the group definition to
   indicate repetition.

      orders [ *( 1*5 server, cluster_controller ) ]

3.6.  Any Value and Any Member

   It is possible to specify that a value can be of any type allowable
   by JSON using the any value rule.  This is done with the 'any'
   literal in a value rule:

      rule_name : any



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   However, unlike other value rules which define primitive data types,
   this rule defines a value of any kind, either primitive (null,
   boolean, number, string), object, or array.

   Use of the any value rule in arrays can be used with repetition to
   define arrays that may contain any value:

      any_value : any

      array_of_any [ *any_value ]

   Specifying any object member name in a member rule with the any
   member rule is done by pre-pending a carat character ('^') to an
   empty member name (that is, ^"" signifies any member name).  This has
   the following form:

      rule_name ^"" target_rule_name

   As an example, the following defines an object member with any name
   that has a value that is a string:

      user_data ^"" : string

   Usage of the any member rule must still satisfy the criteria that all
   member names of an object be unique.

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

      rule_name ^"" : any

   Unlike other types of member rules, it is possible to use repetition
   with the any member rule in an object rule.  The repetition syntax
   and semantics are the same as the repetition syntax and semantics of
   repetition with array rules.  The following example rules define an
   object that may contain any number of members where each member may
   have any value.

      any_member ^"" : any

      object_of_anything { *any_member }

   Use of the repetition of any member rules must satisfy the criteria
   that all member names of an object be unique.







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3.7.  A Root Rule

   In some contexts it is necessary that there be a rule that defines
   the outer most JSON object or array, or if thought of as an inverted
   object tree the structure at the very top.  If in a collection of
   rules there is no rule explicitly specified for this purpose and a
   rule named "root" is given, it can be assumed to be the outer most
   JSON structure or the root of an object/array tree.  If a rule is
   explicitly specified other than "root" and there exists a rule named
   "root", that rule name holds no special meaning.

4.  Directives

   Directives change the interpretation of a collection of rules.  They
   begin with a hash character ('#') and are terminated by the end of a
   line.  They take the following form:

      # directive_name

   Directives may have other qualifiers after the directive name.  They
   may appear intermixed with rules but cannot appear in a rule
   definition.

4.1.  pedantic

   This directive specifies that objects with undefined members should
   not be valid.  Without this directive, an object with undefined
   members will be valid and the undefined members will be ignored.

4.2.  language-compatible-members

   This directive specifies that every member name of every object,
   either explicitly defined or specified via an any member rule or the
   ignore-unknown-members directive must be a name compatible with
   programming languages.  The intent is to specify object member names
   that may be promoted to first-order object attributes or methods in
   an API.  The following ABNF describes the restrictions upon the
   member names:

   ABNF for programming language compatible JSON names


   name = ALPHA *( ALPHA / DIGIT / "_" )


                                 Figure 7





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4.3.  include

   This directive specifies that another collection of rules should be
   evaluated before the rules following this directive.  This directive
   must be qualified with a URL of a file containing the rules
   collection.

      # include http://example.com/rfcXXXX

   In practice this directive should be accompanied by a comment
   describing the rules to include.

      # include http://example.com/rfcXXXX ;Section 3 of RFC XXXX

5.  ABNF Syntax

   The following ABNF describes the syntax for JSON Content Rules.

   grammar         = 1*(rule / directive) *c-wsp

   rule            = rulename definition
   definition      = *c-wsp ( value-rule /
                              member-rule /
                              array-rule /
                              object-rule /
                              group-rule )

   ; rulenames must be unique, and may not be a reserved word
   ; rulenames are case sensitive
   rulename        = *c-wsp ALPHA *(ALPHA / DIGIT / "-" / "_")

   ; Adapted from the ABNF for JSON, RFC 4627 s 2.4
   float           = [ "-" ] int [ frac ] [ exp ]
   integer         = [ "-" ] int [ exp ]
   exp             = ( "e" / "E" ) [ "+" / "-" ] 1*DIGIT
   frac            = "." 1*DIGIT
   int             = "0" / ( %x31-39 *DIGIT )

   ; The regex-char rule allows for any sequence of characters,
   ; including whitespace and newlines, with backslash only
   ; allowed before either a forward or a backslash.
   regex-char      = %x21-2E / %x30-5D / %x5E-7E / WSP /
                     CR / LF / "\/" / "\\"

   ; The defintion of a JSON string, from RFC 4627 s 2
   q-string        = %x20-21 / %x23-5B / %x5D-10FFFF / "\" (
                       %x22 /      ; "  u+0022
                       %x5C /      ; \  u+005C



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                       %x2F /      ; /  u+002F
                       %x62 /      ; BS u+0008
                       %x66 /      ; FF u+000C
                       %x6E /      ; LF u+000A
                       %x72 /      ; CR u+000D
                       %x74 /      ; HT u+0009
                       ( %x75 4HEXDIG ) ) ; uXXXX u+XXXX

   enum-items      = float / integer /
                     "1" / "0" / "true" / "false" /
                     "null" /
                     q-string

   boolean-type    = "boolean"
   null-type       = "null"
   integer-type    = "integer" [ 1*c-wsp integer ".." integer ]
   float-type      = "float"   [ 1*c-wsp float   ".." float   ]
   string-type     = "string"  [ *c-wsp "/" *regex-char "/" ]
   uri-type        = "uri"     [ URI ] ; URI defined in RFC 3986
   ip-type         = "ip4" / "ip6"
   dns-type        = "fqdn" / "idn"
   date-type       = "date-time" / "full-date" / "full-time"
   email-type      = "email"
   phone-type      = "phone"
   base64-type     = "base64"
   enum-type       = "<" 1*( 1*c-wsp enum-items) 1*c-wsp ">"
   any-type        = "any"

   value-rule      = ":" *c-wsp type-rule
   type-rule       = boolean-type /
                     null-type /
                     integer-type /
                     float-type /
                     string-type /
                     uri-type /
                     ip-type /
                     dns-type /
                     date-type /
                     email-type /
                     phone-type /
                     base64-type /
                     enum-type /
                     any-type

   inline-rule     = *c-wsp ( rulename / definition )

   member-rule     = (
                       ( "^" %x22.22 ) /



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                       ( %x22 *q-string %x22 )
                     ) inline-rule

   and-or          = ( "," / "/" )
   object-rule     = "{" object-member *(
                                          *c-wsp
                                          and-or
                                          object-member
                                        ) *c-wsp "}"

   object-items    = ( rulename / member-rule / group-rule )
   object-member   = *c-wsp ["?"] *c-wsp object-items

   array-rule      = "[" array-member *(
                                         *c-wsp
                                         and-or
                                         array-member
                                       ) *c-wsp "]"

   array-count     = *c-wsp [
                              [int]
                              *c-wsp
                              "*"
                              *c-wsp
                              [int]
                              *c-wsp
                            ]
   array-member    = array-count (
                                   rulename /
                                   value-rule /
                                   object-rule /
                                   group-rule )
                     [ *c-wsp "/" array-member ]

   group-rule      = "(" group-member *(
                                          1*c-wsp
                                          and-or
                                          group-member
                                       ) *c-wsp ")"

   group-member    = *c-wsp [ ("?" / array-count ] inline-rule

   directive       = *c-wsp "#" *( VCHAR / WSP / %x7F-10FFFF ) EOL

   ; Taken from the ABNF for ABNF (RFC 4627 section 4) and slightly
   ; adapted newlines in a c-wsp do not need whitespace at the
   ; start of a newline to form a valid continuation line, and
   ; EOL might not be a full CRLF



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   c-wsp           = WSP / c-nl
   c-nl            = comment / EOL
   comment         =  ";" *(WSP / VCHAR) EOL
   EOL             = 1*( CR / LF )

   ; core rules
   ALPHA          =  %x41-5A / %x61-7A   ; A-Z / a-z
   CR             =  %x0D
   DIGIT          =  %x30-39
   HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
   LF             =  %x0A
   VCHAR          =  %x21-7E
   WSP            =  SP / HTAB
   SP             =  %x20
   HTAB           =  %x09

                          JSON Content Rules ABNF

6.  Acknowledgements

   Byron Ellacott provided the original ABNF, from which the current
   ABNF is derived.  Andrew Biggs and Paul Jones provided feedback and
   suggestions which led to many changes in the syntax.

7.  Normative References

   [RFC1166]  Kirkpatrick, S., Stahl, M., and M. Recker, "Internet
              numbers", RFC 1166, July 1990.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.




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   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570, March 2012.

Appendix A.  Comparison with JSON Schema

   This section compares this specification, JSON Content Rules, with
   JSON Schema using examples.

A.1.  Example 1 from RFC 4627

   Example JSON lifted from RFC 4627

   [
       {
          "precision": "zip",
          "Latitude":  37.7668,
          "Longitude": -122.3959,
          "Address":   "",
          "City":      "SAN FRANCISCO",
          "State":     "CA",
          "Zip":       "94107",
          "Country":   "US"
       },
       {
          "precision": "zip",
          "Latitude":  37.371991,
          "Longitude": -122.026020,
          "Address":   "",
          "City":      "SUNNYVALE",
          "State":     "CA",
          "Zip":       "94085",
          "Country":   "US"
       }
   ]














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   JSON Content Rules

   root [
       2*2{
           "precision" : string,
           "Latitude" : float,
           "Longitude" : float,
           "Address" : string,
           "City" : string,
           "State" : string,
           "Zip" : string,
           "Country" : string
       }
   ]

   JSON Schema

   {
      "type": "array",
      "items": [
          {
              "type": "object",
              "properties": {
                  "precision": { "type": "string", "required": "true" },
                  "Latitude": { "type": "number", "required": "true" },
                  "Longitude": { "type": "number", "required": "true" },
                  "Address" : { "type": "string", "required": "true" },
                  "City" : { "type": "string", "required": "true" },
                  "State" : { "type" : "string", "required": "true" },
                  "Zip" : { "type" : "string", "required": "true" },
                  "Country" : { "type" : "string", "required": "true" }
              }
          }
      ],
      "minItems" : 2,
      "maxItems" : 2
   }

A.2.  Example 2 from RFC 4627












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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]
      }
   }

   JSON Content Rules

   width "width" : integer 0..1280
   height "height" : integer 0..1024

   root {
       "Image" {
           width, height, "Title" :string,
           "thumbnail" { width, height, "Url" :uri },
           "IDs" [ *:integer ]
       }
   }

   JSON Schema

   {
       "type" : "object",
       "properties" : {
           "Image": {
               "type" : "object",
               "properties" : {
                   "Width" : {
                       "type" : "integer",
                       "minimum" : 0,
                       "maximum" : 1280,
                       "required" : "true"
                   }
                   "Height" : {
                       "type" : "integer",
                       "minimum" : 0,
                       "maximum" : 1024,
                       "required" : "true"



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                   }
                   "Title" : { "type": "string" },
                   "Thumbnail" : {
                       "type" : "object",
                       "properties" : {
                           "Url" : {
                               "type" : "string",
                               "format" : "uri",
                               "required" : "true"
                           },
                           "Width" : {
                               "type" : "integer",
                               "minimum" : 0,
                               "maximum" : 1280,
                               "required" : "true"
                           },
                           "Height" : {
                               "type" : "integer",
                               "minimum" : 0,
                               "maximum" : 1280,
                               "required" : "true"
                           }
                       }
                   },
                   "IDs" : {
                       "type":"array",
                       "items":[ { "type": "integer" } ],
                       "required" : "true"
                   }
               }
           }
       }
   }

Appendix B.  A "Real World" Exmaple

   The following example is taken from draft-ietf-weirds-json-response-
   00.  It describes the entity object (Section 4), the nameserver
   object (Section 5) and many of the other sub-structures used in
   objects defined in other sections of that draft.

   JSON Content Rules for nameserver and entity from draft-ietf-weirds-
   json-response

   # language-compatible-members

   ; the nameserver object
   ; models nameserver host information



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   ; this often referred to as 'host' object too
   nameserver {

     ; the host name of the name server
     "name" : fqdn,

     ; the ip addresses of the nameserver
     "ipAddresses" [ *( :ip4 / :ip6 ) ],

     common
   }

   ; the entity object
   ; This object object represents the information of organizations,
   ; corporations, governments, non-profits, clubs, individual persons,
   ; and informal groups of people.
   entity {

     ; the names by which the entity is commonly known
     "names" [ *:string ],

     ; the roles this entity has with any containing object
     "roles" [ *:string ],

     ; the place where the person, org, etc... receives postal mail
     ; THIS IS NOT LOCATION
     "postalAddress" [ *:string ],

     ; electronic mailboxes where the person, org, etc...
     ; receives messages
     "emails" [ *:email ],

     ; phones where the person, org, etc... receives
     ; telephonic communication
     "phones" {
         "office" [ *:phone ], ; office phones
         "fax" [ *:phone ],    ; facsilime machines
         "mobile" [ *:phone ]  ; cell phones and the like
     },

     common
   }

   ; The members "handle", "status", "remarks", "uris", "port43",
   ; "sponsoredBy", "resoldBy", "registrationBy", "registrationDate",
   ; "lastChangedDate", and "lastChangedBy" are used in many objects
   common (




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     ; a registry-unique identifier
     "handle" : string,

     ; an array of status values
     "status" [ *:string ],

     ; an array of strings, each containing comments about the object
     "remarks" [ *:string ].

     ; an array of uri objects
     ; "type" referrs to the application of the URI
     ; "uri" is the uri
     "uris" [
       *{ "type" : string, "uri" : uri }
     ],

     ; a string containing the fully-qualified host name of the
     ; WHOIS [RFC3912] server where the object instance may be found
     "port43" : fqdn,

     ; a string containing an identifier of the party
     ; through which the registration was made, such as an IANA approved
     ; registrar
     "sponsoredBy" : string,

     ; a string containing an identifier of the party
     ; originating the registration of the object.
     "resoldBy" : string,

     ; a string containing an identifier of the party
     ; responsible for the registration of the object
     "registrationBy" : string,

     ; the date the object was registered
     "registrationDate" : date-time,

     ; the date of last change made to the object
     "lastChangedDate" : date-time,

     ; a string containing an identifier of the party
     ; responsible for the last change made to the registration
     "lastChangedBy" : string
   )








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Appendix C.  Design Notes

C.1.  Member Uniqueness

   JSON does not disallow non-unique object member names ( in other
   words, it allows non-unique object member names ) but strongly
   advises against the use of non-unique object member names.  Many JSON
   implementations use hash-indexed maps to represent JSON objects,
   where the object's member names are the key of the hash index.  Non-
   uniqueness would break such implementations or result in the value of
   the last member given overwriting the value of all previous members
   of the same name.

   Therefore, allowing non-unique object member names would be bad
   practice.  For this reason, this specification does not accommodate
   the need for non-unique object member names.

C.2.  Member Order

   JSON gives awkward guidance regarding ordering of object member
   names.  However, many JSON implementations use hash-indexed maps to
   represent JSON objects, where the object's member names are the key
   of the hash index.  Though it is possible, usually these maps have no
   explicit order as the only index is the hash.

   Therefore, this specification does not provide a means to imply order
   of object member names.

C.3.  Group Syntax for Arrays and Objects

   It is possible to create a separate group syntax for array rules vs
   object rules, since allowable group rule content is determined by the
   containing rule.  For instance, while the syntax for groups in
   objects could have been "( blah blah )", syntax for groups in arrays
   could have been "< blah blah >".  That may be more distinctive and
   allow the formal syntax parser to handle rule content validity, but
   the added extra syntax appeared to hurt readability.  There is only
   so many enclosure characters a person should reasonably be required
   to know, and adding yet another did not seem prudent.

C.4.  Inspiration

   The original approach to this problem was to find a concise way to
   describe JSON data structures; to do for JSON what RelaxNG compact
   syntax does for XML.  The syntax itself hopefully has a JSON-ness or
   a JSON feel to it.  And a good bit of inspiration came from ABNF.





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C.5.  Changelog

   From -00 to -01

   1.  Added ABNF.  Thanks Byron Ellacott.

   2.  Added section about root rules.

   3.  Other minor edits.

   From -01 to -02

   1.  Other minor edits.

   2.  Added the Possible Future Changes section.

   3.  Mostly a keep-alive version.

   From -02 to -03

   1.  Removed formal syntax (ABNF) until such time as the features are
       nailed down.  It will appear in a future draft.

   2.  Took out the option for multiple email conformance levels as
       everything should be conformant to RFC 5322.

   3.  URIs conformance can now either be just 'uri' or match a URI
       template (suggestion from Andrew Biggs).

   4.  Added enumerated values based on a suggestion from Paul Jones.

   5.  Added a directive for including other collections of rules.

   6.  Added an example of object mixins using groups thanks to a
       discussion with Andrew Biggs.

   7.  Added an alternate syntax mapping.

   From -03 to -04

   1.  Removed the alternate syntax.  Nobody liked it.

   2.  all-members-optional directive was removed.

   3.  ignore-unknown-members directive was removed.

   4.  pedantic directive was added.




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   5.  Modified the include directive syntax.

   6.  Removed the depends operator.

   7.  Added syntax for optional members of groups in object rules.

   8.  Added syntax for repetition for elements of groups in array
       rules.

   9.  ABNF added back.

Author's Address

   Andrew Lee Newton
   American Registry for Internet Numbers
   3635 Concorde Parkway
   Chantilly, VA  20151
   US

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






























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