<bookstore>
<book category="Programming">
<title lang="en">Coding</title>
<publisher>ErBooks</publisher>
<field>web</field>
<field>programming</field>
<field>C++</field>
</book>
<book category="XML">
<title lang="en">Hey XML</title>
<publisher>BookyBooks</publisher>
<field>web</field>
<field>xml</field>
<field>database</field>
</book>
<book category="WEB">
<title lang="en">XQuery Kick Start</title>
<publisher>Penguin</publisher>
<field>web</field>
<field>design</field>
<field>database</field>
</book>
我想检索每个出版商都出版过书籍的字段(在这个示例中是“网络”)。
伪代码:如果所有发布者 = fieldX 返回 fieldX