问题描述
我正在使用 XSD，我可以从 XSD 以字符串形式访问模式.一个例子:
I am working with XSDs, and I have access to the pattern from the XSD as a string. An example:
<xsd:pattern value="[0-9]{8}"/>
给我 C# 字符串
string pattern = "[0-9]{8}";
从我从 XSD 获得的模式字符串(可以是任何有效的 XSD 模式条目)，我试图计算出 XML 中字段内容的最大可能长度.
From the pattern string I obtain from the XSD (which could be any valid XSD pattern entry), I am trying to work out the maximum possible length the contents of the field in the XML can be.
在这个简单的例子中，它显然是 8 - 我可以通过检查 {n} 并假设这是长度来计算出来.在其他模式中，我也可以检查 * 或 + 并假设无界 - 但我正在寻找一种更通用的方法来实现这一点.
In this trivial example, it's obviously 8 - I could figure that out by checking for {n} and assuming that's the length. In other patterns I could also check for * or + and assume unbounded - but I am looking for a more general approach that can be used to do this.
请注意，不保证模式字符串与 .Net 的 Regex 类兼容.
Note that the pattern string is not guaranteed to be compatible with .Net's Regex classes.
我还可以访问 XmlSchemaPatternFacet 类，如果有帮助的话，我首先用它来解析 XSD.
I also have access to the XmlSchemaPatternFacet class, which is what I'm using to parse the XSD in the first place, if that's any help.
感谢您提供的任何帮助
推荐答案
您几乎肯定需要解析正则表达式来实现这一点.例如，您可以采用 Saxon 中的开源正则表达式解析器(它实现了正确的正则表达式方言).这将创建一个子表达式树，您可以添加一个方法来计算树中每个节点的最大匹配长度.Operation 类，代表树中的一个节点，已经(在 9.6 中)有方法 getMatchLength() 和 getMinimumMatchLength()，它会很容易添加一个以相同方式工作的 getMaximumMatchLength().
You'll almost certainly need to parse the regular expression to achieve this. For example you could take the open-source regular expression parser in Saxon (which implements the right regex dialect). This creates a tree of subexpressions, and you could add a method to compute the maximum match length for each node in the tree. The Operation class, representing a node in the tree, already (in 9.6) has methods getMatchLength() and getMinimumMatchLength(), and it would be easy enough to add a getMaximumMatchLength() that works the same way.
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