A Language for Rules Describing JSON Content
draft-newton-json-content-rules-08
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draft-newton-json-content-rules-08
Network Working Group A. Newton
Internet-Draft ARIN
Intended status: Standards Track P. Cordell
Expires: September 29, 2017 Codalogic
March 28, 2017
A Language for Rules Describing JSON Content
draft-newton-json-content-rules-08
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.
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Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 29, 2017.
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
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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. ABNF Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 32
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.1. Normative References . . . . . . . . . . . . . . . . . . 38
9.2. Infomative References . . . . . . . . . . . . . . . . . . 38
Appendix A. Co-Constraints . . . . . . . . . . . . . . . . . . . 39
Appendix B. Testing Against JSON Content Rules . . . . . . . . . 39
B.1. Locally Overriding Rules . . . . . . . . . . . . . . . . 39
B.2. Rule Callbacks . . . . . . . . . . . . . . . . . . . . . 40
Appendix C. JCR Implementations . . . . . . . . . . . . . . . . 40
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Appendix D. Syntax Changes from -06 and -07 . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
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.
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
$referrer_uri = "referrerURI" : uri
Figure 69
7. ABNF Syntax
The following ABNF describes the syntax for JSON Content Rules. A
text file containing these ABNF rules can be downloaded from
[JCR_ABNF].
jcr = *( sp-cmt / directive / root-rule / rule )
sp-cmt = spaces / comment
spaces = 1*( WSP / CR / LF )
DSPs = ; Directive spaces
1*WSP / ; When in one-line directive
1*sp-cmt ; When in muti-line directive
comment = ";" *comment-char comment-end-char
comment-char = HTAB / %x20-10FFFF
; Any char other than CR / LF
comment-end-char = CR / LF
directive = "#" (one-line-directive / multi-line-directive)
one-line-directive = [ DSPs ]
(directive-def / one-line-tbd-directive-d)
*WSP eol
multi-line-directive = "{" *sp-cmt
( directive-def /
multi-line-tbd-directive-d )
*sp-cmt "}"
directive-def = jcr-version-d / ruleset-id-d / import-d
jcr-version-d = jcr-version-kw DSPs major-version
"." minor-version
*( DSPs "+" [ DSPs ] extension-id )
major-version = non-neg-integer
minor-version = non-neg-integer
extension-id = ALPHA *not-space
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ruleset-id-d = ruleset-id-kw DSPs ruleset-id
import-d = import-kw DSPs ruleset-id
[ DSPs as-kw DSPs ruleset-id-alias ]
ruleset-id = ALPHA *not-space
not-space = %x21-10FFFF
ruleset-id-alias = name
one-line-tbd-directive-d = directive-name
[ WSP one-line-directive-parameters ]
directive-name = name
one-line-directive-parameters = *not-eol
not-eol = HTAB / %x20-10FFFF
eol = CR / LF
multi-line-tbd-directive-d = directive-name
[ 1*sp-cmt multi-line-directive-parameters ]
multi-line-directive-parameters = multi-line-parameters
multi-line-parameters = *(comment / q-string / regex /
not-multi-line-special)
not-multi-line-special = spaces / %x21 / %x23-2E / %x30-3A /
%x3C-7C / %x7E-10FFFF ; not ", /, ; or }
root-rule = value-rule / group-rule
rule = annotations "$" 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
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 )
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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
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 ]
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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 (*( sequence-combiner object-item ) /
*( choice-combiner object-item ) )
object-item = object-item-types *sp-cmt [ repetition ]
object-item-types = object-group / member-rule / target-rule-name
object-group = "(" *sp-cmt [ object-items *sp-cmt ] ")"
array-rule = annotations "[" *sp-cmt [ array-items *sp-cmt ] "]"
array-items = array-item (*( sequence-combiner array-item ) /
*( choice-combiner array-item ) )
array-item = array-item-types *sp-cmt [ repetition ]
array-item-types = array-group / type-rule / explicit-type-choice
array-group = "(" *sp-cmt [ array-items *sp-cmt ] ")"
group-rule = annotations "(" *sp-cmt [ group-items *sp-cmt ] ")"
group-items = group-item (*( sequence-combiner group-item ) /
*( choice-combiner group-item ) )
group-item = group-item-types *sp-cmt [ repetition ]
group-item-types = group-group / member-rule /
type-rule / explicit-type-choice
group-group = group-rule
sequence-combiner = *sp-cmt "," *sp-cmt
choice-combiner = *sp-cmt "|" *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 ]
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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
%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
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;; 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"
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
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8. Acknowledgements
John Cowan, Andrew Biggs, Paul Kyzivat and Paul Jones provided
feedback and suggestions which led to many changes in the syntax.
9. References
9.1. 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.
[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.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, August 2010.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
[JCR_ABNF]
Newton, A. and P. Cordell, "ABNF for JSON Content Rules",
<https://raw.githubusercontent.com/arineng/jcr/08/jcr-
abnf.txt>.
9.2. 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.
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[JCR_SPECIFICATION_FIGURES]
Newton, A. and P. Cordell, "Figures in the JCR
Specification", <https://github.com/arineng/jcr/tree/08/
figs>.
[ARIN_JCR_VALIDATOR]
American Registry for Internet Numbers, "JSON Content
Rules Validator (Work In Progress)",
<https://github.com/arineng/jcrvalidator>.
[CODALOGIC_JCR_VALIDATOR]
Codalogic, "cl-jcr-parser (Work In Progress)",
<https://github.com/codalogic/cl-jcr-parser>.
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).
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.
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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.
$statuses = @{unordered} @{not} [ "denied" + , string * ]
Figure 74
[ "submitted", "validated", "denied" ]
Figure 75
B.2. Rule Callbacks
In many testing scenarios, the evaluation of rules may become more
complex than that which can be expressed in JCR, sometimes involving
variables and interdependencies which can only be expressed in a
programming language.
A JCR processor may provide a mechanism for the execution of local
functions or methods based on the name of a rule being evaluated.
Such a mechanism could pass to the function the data to be evaluated,
and that function could return to the processor the result of
evaluating the data in the function.
Appendix C. JCR Implementations
The following implementations, [ARIN_JCR_VALIDATOR] and
[CODALOGIC_JCR_VALIDATOR] have influenced the development of this
document.
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Appendix D. Syntax Changes from -06 and -07
The differences between this document and -07 are not significant, as
this version of this draft is provided for the purposes of keeping
the document active within the IETF archives.
The syntax described in this document is changed significantly, and
in a non-backwards compatible manner, from the syntax described in
the -06 version of this specification. The vast majority of these
changes have occurred to meet the goals of the syntax being a
superset of JSON and easy to comprehend by a casual reader unfamiliar
with JCR but familiar with JSON.
The latter of those two goals is subjective, and therefore a series
of focus group sessions were convened where participants, all
professional software developers with familiarity with JSON but not
JCR, were asked to read and interpret various rulesets and allowed to
offer suggested improvements. Outcomes of these sessions resulted in
many changes, such as the use of '$' characters to note rule names
and the change of the repetition syntax.
Other changes came from feedback given directly to the authors via
email and on the IETF JSON Working Group mailing list.
Most figures from this document can be found in file form at
[JCR_SPECIFICATION_FIGURES].
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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