W3C: Can't read EBNF's SPARQL IRIREF specification?

Question

(Specifications: https://www.w3.org/TR/sparql11-query/#rIRIREF)

According to the specification, an IRIREF can be parsed as this:

[139]   IRIREF    ::=   '<' ([^<>"{}|^`\]-[#x00-#x20])* '>'

What is bothering me is this part of the expression:

\]-[

If I consider \ to be an escaping character in the bracketed character class (which would be the case in a Perl regular expression), then it means the \ alone is not a problem in the IRIREF and this is valid: <http://hello\world>

Then there is this big problem with the range: ]-[. The character ] has an ordinal value of 93 and the [ of 91. This means we have an invalid range: 93 to 92. This is not allowed in most regex engines I tested.

What does that means?

1. Should I consider the - as a regular character in the bracketed character class, then this is invalid IRIREF: <http://new-example.org>. It makes no sense.
2. Should I consider the range ]-[ null and this IRIREF is valid: <http://hello[world]>
3. What I think is more likely is that the range is inverted and is not a problem for w3c specifications, which means the characters [, \ and ] are invalid characters. This makes sense.

Answer 1

这是简写的句法糖，EBNF确切地说，是一种超越regexen标准功能的语法：

这意味着prior character class without following character class，在此特定情况下为not certain brackets and quotes, and neither control codes from 0x00 (NUL) to 0x20 (SPC), which would otherwise be included。

相关参考：EBNF notation used，特别是A - B条款。它在SPARQL grammar的第一段中提及。

Answer 2

SPARQL规范说它的语法是用符号defined by the XML 1.1 specification编写的。

在那个符号中，你引用右边的那个，

'<' ([^<>"{}|^`\]-[#x00-#x20])* '>'

表示

的序列

• a＆＃39;＆lt;＆＃39;字符

• 与表达式匹配的零个或多个字符[^＆lt;＆gt;＆＃34; {} | ^`] - [＃x00-＃x20];这是表示

  的设定差异
  • 由[^＆lt;＆gt;＆＃34; {} | ^ \] = any character other than '<', '>', '"', '{', '}', '|', '^', '＆＃39;或＆＃39; \＆＃39;匹配的任何字符;注： ＆＃39; \＆＃39;这个符号中没有转义字符（根本没有转义字符）
  • 除了那些匹配[＃x00-＃x20] =控制字符的C1区域加空白

  编写此模式有点奇怪;它同样可以写成[^＆lt;＆gt;＆＃34; {} | ^`＃x00-＃x20];我不确定为什么编辑会按照他们的方式写出来。

• a＆＃39;＆gt;＆＃39;字符

所以逐一回答你的问题：

  

我应该考虑 - 作为括号中的字符类中的常规字符，那么这是无效的IRIREF：http://new-example.org。这毫无意义。

没有。当 A 和 B 是此表示法中的表达式时， A - B 表示 A ，也不是 B 语言的字符串。这里 A 和 B 是每个字符类表达式，一个是负数，一个是正数。

你是对的，禁止用于接受尖括号括号内的IRI的语法规则中的连字符是没有意义的。

  

我应该考虑范围] - [null且此IRIREF有效：http://hello[world]

＆＃39;] - [＆＃39;不表示此处的范围，null或其他; ]结束第一个字符类表达式，[结束第二个字符表。

  

我认为更有可能的是，范围是反转的，对于w3c规范来说不是问题，这意味着字符[，\和]是无效字符。这是有道理的。

如果我对表达式的解析是正确的，＆＃39; [＆＃39;和＆＃39;]＆＃39;是合法的（第一个表达不排除它们，第二个表达不排除它们）; ＆＃39; \＆＃39;被第一个表达式排除。