XQuery:返回多个元素 [英] XQuery: Returning more than one element

问题描述

以下是描述我正在使用的 XML 结构的 DTD:

The following is the DTD describing the structure of the XML I am working with:

<!DOCTYPE bib [
<!ELEMENT bib (book+,magazine*)>
<!ELEMENT book (title,author+,publisher,editor?,price)>
<!ELEMENT magazine (title,publisher,editor+)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT author (last,first)>
<!ELEMENT publisher (#PCDATA)>
<!ELEMENT editor (last, first,affiliation)>
<!ELEMENT price ((#PCDATA)>
<!ELEMENT last (#PCDATA)>
<!ELEMENT first (#PCDATA)>
<!ELEMENT affiliation (#PCDATA)>
<!ATTLIST book year CDATA #REQUIRED>
]>

我必须编写一个 XQuery 来返回 Weikum 先生是其中一位编辑的所有书籍或杂志.

I have to write an XQuery to return all books or magazines where Mr. Weikum is one of the editors.

我在确定如何归还书籍或杂志时遇到问题.这是我能想到的:

I am having a problem in determining how to return book or magazine. This is what I can come up with:

for $x in document("bib.xml")/bib
where $x/book/editor/lastname = "Weikum" or $x/magazine/editor/lastname = "Weikum"
return <result></result>

但这并没有达到我想要的结果.如何退回书籍或杂志元素?我应该说 return $x 吗?

But this is not achieving my desired result. How can I return the book or magazine element? Should I just say return $x?

推荐答案

返回姓氏为Weikum"的编辑的书籍和杂志的最简单方法是

The simplest way to return books and magazines with an editor whose last name is 'Weikum' would be

//editor[lastname='Weikum']/..

或者，如果您更喜欢 FLWOR 表达式，是的，您可以直接说 return $x，如果 $x 绑定到您要返回的内容.但是，在您的草图中，情况并非如此:您说要归还书籍或杂志，但您已将 $x 绑定到 bib 元素.你想要更像这样的东西:

Or, if you prefer a FLWOR expression, yes, you can just say return $x, if $x is bound to what you want to return. That's not true in your sketch, however: you say you want to return the book or magazine, but you have bound $x to the bib element. You want something more like this:

for $x in document('bib.xml')/bib/*
where $x/editor/lastname='Weikum'
return $x

在这两个公式中，我利用了这样一个事实，即只有书籍和杂志才有名为 editor 的子项，并且只有书籍和杂志才会显示为 bib 的子项.在更复杂的 DTD 中，如果您需要过滤掉小册子、标准和博客文章以便只是书籍和杂志...

In these two formulations I am exploiting the fact that only books and magazines have children named editor, and that only books and magazines appear as children of bib. In a more complicated DTD, you might need more complex expressions if you needed to filter out pamphlets, standards, and blog posts in order to get just books and magazines ...

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