- See UTR 17, Unicode Character Encoding Model - if you're brave enough to tackle the mysteries of CCSs, CEFs, CESs, etc.
- See also Sections 3.8, 9, 10 of Unicode 5 for more punishment.
- See also the ICU page for lots of detailed documentation on how Unicode is supposed to work in running, software, including discussions of what can possibly go wrong.
- There are three "encoding" forms, UTF-8, UTF-16, and UTF-32; there are also UCS-2 and UCS-4.
- JSON must be unicode
- The default encoding form of JSON is utf-8 unicode, which effectively means it must be supported, but JSON data can also be delivered in the other two forms
- SPARQL syntax is UTF-8 Unicode: "The encoding is always UTF-8 [RFC3629]. Unicode code points may also be expressed using an \uXXXX (U+0 to U+FFFF) or \UXXXXXXXX syntax (for U+10000 onwards) where X is a hexadecimal digit [0-9A-F]". In other words, the SPARQL must detect and reject non-utf-8. But it isn't clear if a conformant SPARQL parser must accept unicode expressed with escapes (which is essentially utf-7).
- The XML header of a result should always explicitly declare the encoding
- Content negotiation (Accept-Charset, Content-Type 'charset' parameter, etc.) should be used to specify encodings and forms
- A SPARQL query whose Accept header specifies JSON must always return results in utf-8 if no other Charset is requested
- Joda "Joda-Time provides a quality replacement for the Java date and time classes."
ICU Collation documentation
XQuery/XPath collation documentation
SPARQL¶SPARQL does not define a collation order, though one could be used for any undefined comparison. Examples of undefined comparisons include:
- "a" and "a"@en_gb (a simple literal and a literal with a language tag)
- "a"@en_gb and "b"@en_gb (two literals with language tags)
- "a" and "a"^^xsd:string (a simple literal and an xsd:string)
- Comparisons between language-coded literals.
- User access (through FILTER, LET, or HAVING) to an implementation of fn:compare.
Currently, we don't know of any projects that implement fn:compare.
- Acceptance and conversion of other encodings for incoming data?
- Date comparisons?
- Other locale-specific logic?