Internet Engineering Task Force A. Boronine, Ed.
Internet-Draft December 2014
Intended status: Informational
Expires: June 4, 2015
Minimal JSON Type System
draft-boronine-teleport-02
Abstract
Teleport is a minimal type system designed as an extension of JSON.
It comes with 10 types sufficient for basic use and provides two
patterns for extending it with new types. Teleport's type
definitions are JSON values, for example, an array of strings is
defined as {"Array": "String"}.
Teleport implementations can be used for data serialization, input
validation, for documenting JSON APIs and for building API clients.
This document provides the mathematical basis for Teleport and can be
used for implementing libraries.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Type Patterns . . . . . . . . . . . . . . . . . . . . . . . . 3
4. JSON Schemas . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Mathematical Basis . . . . . . . . . . . . . . . . . . . . . 4
5.1. Concrete Types . . . . . . . . . . . . . . . . . . . . . 4
5.2. Generic Types . . . . . . . . . . . . . . . . . . . . . . 4
6. Built-in Concrete Types . . . . . . . . . . . . . . . . . . . 4
7. Built-in Generic Types . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Mailing List . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
In Teleport, a type is a relation between a type definition and a
value space. For example:
t("Integer") = {0, -1, 1, -2, 2, -3, 3, ...}
Here "Integer" is a type definition and t("Integer") is the set of
all values this type can take. The t function is used to represent
this relationship.
Because Teleport is based on JSON, all value spaces are sets of JSON
values. More interestingly, type definitions are JSON values too,
which makes it trivial to share them with other programs.
Teleport's design goals is to be a natural extension of JSON, be
extremely lightweight, and extendable not only with rich types but
with high-level type system concepts.
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2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
The terms "JSON", "JSON text", "JSON value", "member", "element",
"object", "array", "number", "string", "boolean", "true", "false",
and "null" in this document are to be interpreted as defined in RFC
4627 [RFC4627].
2.1. Syntax
Throughout this document, an extended JSON syntax is used. Unquoted
strings are symbols representing JSON values, sets and functions.
Also, the following set theory syntax is used:
a :: A Set A contains element a.
D -> C The set of functions that map values from set D to values
from set C.
3. Type Patterns
Types defined simply by a string, like "Integer" above, are called
concrete. Teleport ships with 7 concrete types.
A generic type maps a set of schemas to a set of value spaces. Each
pair in the mapping is called an instance. For example, {"Array":
"Integer"} is an instance of the Array type.
Three generic types are provided: Array, Map and Struct. Their
precise definition is provided in the following sections, but these
examples should be enough to understand how they work:
["foo", "bar"] :: t({"Array": "String"})
{"a": 1, "b": 2} :: t({"Map": "Integer"})
{"name": "Alexei"} :: t({"Struct": {
"required": {"name": "String"},
"optional": {"age": "Integer"}})
4. JSON Schemas
Schema, one of the build-in concrete types, is made possible by the
fact that type definitions are JSON values. The Schema type is
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useful to specify APIs. For example, to describe a function you can
use this:
t({"Struct": {
"optional": {},
"required": {
"input": "Schema",
"output": "Schema"}}}
5. Mathematical Basis
The set of all JSON values is called V. A subset of V is called a
value space and the set of all value spaces is called S.
V = {null, true, false, 0, 1, 2, 3, 4, ...}
S = {{}, {null}, {null, true}, {null, ...}, ...}
There is a certain function t that maps JSON values to value spaces.
t :: (V -> S)
This document does not give a full definition of the t function, it
merely provides some instances of its inputs and outputs. Expanding
the definition of the t function is the basis for extending Teleport.
5.1. Concrete Types
x is of concrete type c if and only if
1. c is a string
2. x :: t(c).
5.2. Generic Types
x is of generic type g if and only if
1. g is a string
2. x :: t({g: p}) for some p
6. Built-in Concrete Types
JSON t("JSON") is the set of all JSON values. This type can be
used as a wildcard for type-checking or as a noop for
composable serialization.
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Schema t("Schema") is the set of all type definitions, including
all strings representing concrete types as well as every
instance of every generic type.
Decimal t("Decimal") is the set of all numbers. This type
represents real numbers and arbitrary-precision
approximations of real numbers.
Integer t("Integer") is the set of all numbers that don't have a
fractional or exponent part.
String t("String") is the set of all strings. Note that JSON
strings are sequences of Unicode characters.
Boolean t("Boolean") is a set containing the JSON values true and
false.
DateTime t("DateTime") is the set of all strings that are valid
according to RFC 3339 [RFC3339]. This type represents
typestamps with optional timezone data.
7. Built-in Generic Types
x :: t({"Array": p}) if and only if
x is an array
e :: t(p) for every element e in x
x :: t({"Map": p}) if and only if
x is an object
v :: t(p) for every pair (k, v) in x
x :: t({"Struct": p}) if and only if
p is an object with at least two members: required and optional.
Both are objects and their names are disjoint, that is, they don't
have a pair of members with the same name.
x is an object. The name of every member of p.required is also
the name of a member of x.
For every pair (k, v) in x, there is a pair (k, s) in either
p.required or p.optional such that v :: t(s).
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NOTE: the definition of Struct implies that its parameter p can
contain arbitrary metadata in the form of other object members.
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
All drafts are required to have a security considerations section.
See RFC 3552 [RFC3552] for a guide.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, .
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627,
DOI 10.17487/RFC4627, July 2006, .
10.2. Informative References
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, .
Appendix A. Mailing List
Comments are solicited and should be addressed to the working group's
mailing list at teleport-json@googlegroups.com and/or the author.
Author's Address
Alexei Boronine (editor)
Email: alexei@boronine.com
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