XSD - A Dart XML Schema Datatypes Interop Library

A Dart library for working with XML Schema Datatypes (XSD) as defined by the W3C. This library provides Dart representations for XSD types and codecs to convert between their lexical (string) forms and their Dart object representations.

The primary goal is to offer a robust and idiomatic way to handle XSD typed data within Dart applications, particularly (but not exclusively) in the context of RDF data processing.

Purpose

This library aims to:

• Provide faithful Dart representations for common XSD built-in datatypes.
• Offer dart:convert style Codec instances for each supported XSD type, allowing for easy encoding (Dart object to XSD string) and decoding (XSD string to Dart object).
• Handle XSD whitespace processing rules (preserve, replace, collapse) correctly.
• Validate lexical forms against the rules of the specific XSD datatype.
• Implement the value space constraints (e.g., ranges for numeric types) defined for each built-in XSD type.

Supported XSD Datatypes

This library aims to support the following XSD 1.1 built-in datatypes that are commonly used in RDF and general XML processing:

XSD Data Type	Planned	Implemented	Dart Data Type	Implementation Source
xsd:boolean	✅	✅	bool	dart:core
xsd:string	✅	✅	String	dart:core
xsd:normalizedString	✅	✅	String	dart:core
xsd:token	✅	✅	String	dart:core
xsd:NMTOKEN	✅	✅	String	dart:core
xsd:Name	✅	✅	String	dart:core
xsd:language	✅	✅	Locale	package:intl
xsd:NCName	✅	✅	String	dart:core
xsd:decimal	✅	✅	Decimal	package:decimal
xsd:double	✅	✅	double	dart:core
xsd:float	✅	✅	double	dart:core
xsd:integer	✅	✅	BigInt	dart:core
xsd:nonPositiveInteger	✅	✅	BigInt	dart:core
xsd:negativeInteger	✅	✅	BigInt	dart:core
xsd:long	✅	✅	BigInt	dart:core
xsd:int	✅	✅	int	dart:core
xsd:short	✅	✅	int	dart:core
xsd:byte	✅	✅	int	dart:core
xsd:nonNegativeInteger	✅	✅	BigInt	dart:core
xsd:positiveInteger	✅	✅	BigInt	dart:core
xsd:unsignedLong	✅	✅	BigInt	dart:core
xsd:unsignedInt	✅	✅	int	dart:core
xsd:unsignedShort	✅	✅	int	dart:core
xsd:unsignedByte	✅	✅	int	dart:core
xsd:anyURI	✅	✅	Uri	dart:core
xsd:hexBinary	✅	✅	Uint8List	dart:typed_data
xsd:base64Binary	✅	✅	Uint8List	dart:typed_data
xsd:duration	✅	✅	XsdDuration[1]	package:xsd
xsd:yearMonthDuration	✅	❌	???	???
xsd:dayTimeDuration	✅	❌	???	???
xsd:dateTime	✅	✅	XsdDateTime[2]	package:xsd
xsd:dateTimeStamp	✅	❌	???	???
xsd:date	✅	✅	XsdDate	package:xsd
xsd:time	✅	❌	???	???
xsd:gYearMonth	✅	✅	YearMonth	package:xsd
xsd:gYear	✅	✅	GregorianYear	package:xsd
xsd:gMonthDay	✅	✅	GregorianMonthDay	package:xsd
xsd:gDay	✅	✅	GregorianDay	package:xsd
xsd:gMonth	✅	✅	GregorianMonth	package:xsd
xsd:QName	❌	❌	❌	❌
xsd:NOTATION	❌	❌	❌	❌
xsd:ID	❌	❌	❌	❌
xsd:IDREF	❌	❌	❌	❌
xsd:ENTITY	❌	❌	❌	❌
xsd:ENTITIES	❌	❌	❌	❌
xsd:NMTOKENS	❌	❌	❌	❌

[1] Note: Although Dart already has a Duration class it actually represents an entirely different concept to the ISO8600 / XSD idea of a duration which XsdDuration implements.

[2] Note: Dart's native DateTime class doesn't preserve the original timezone offset from a parsed string, which is important for round-tripping xsd:dateTime values. This wrapper class stores the original offset to address this.

Limitations

• Facets on Built-in Types: This library focuses on implementing the XSD built-in datatypes as they are defined in the "XML Schema Part 2: Datatypes" specification. This includes their inherent properties, lexical spaces, value spaces, and any fixed facets that define them (e.g., the range of xsd:byte or the whiteSpace behavior of xsd:token).
• The library currently does not provide a mechanism to dynamically apply arbitrary constraining facets (like minLength, maxLength, pattern, enumeration, totalDigits, fractionDigits beyond what defines a base type) to create new, user-defined derived simple types at runtime through the codec. For instance, while xsd:string is supported, you cannot pass maxLength="5" to the XsdStringCodec to validate against this specific restriction dynamically. Such validation would typically be handled by a higher-level XSD schema processor that uses this library for the base datatype conversions.

Usage

(This section will be filled out with examples as more types are completed and the API stabilizes. Basic usage involves selecting the appropriate codec and using its encode or decode methods.)

import 'package:xsd/xsd.dart';

final boolCodec = XsdBooleanCodec();
bool myBool = boolCodec.decode('1'); // true
String boolStr = boolCodec.encode(false); // "false"

final intCodec = XsdIntCodec();
int myInt = intCodec.decode('  -123  '); // -123
String intStr = intCodec.encode(456); // "456"