Compare two sibling nodes' child nodes

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I am very new to Xml and Xquery so I am sorry if this is a stupid question. I have xml code in this format

<myDB>
  <book>
    <title>ebXML : Concepts and Application</title>
    <author>
      <last_name>Smith</last_name>
      <first_name>John</first_name>
   </author>
   <year>2003</year>
   <publisher>Wiley</publisher>
</book>
<article>
  <title>test title</title>
  <author>
    <last_name>Smith</last_name>
    <first_name>John</first_name>
  </author>
  <year>2003</year>
  <publisher>test Wiley</publisher>
</article>
</myDB>

So there are two siblings, 'book' and 'article' They both have children 'author' and 'year' I want to find all authors who have written at least one article and one book in the same year. I thought it would work if I used this as a predicate

//author[//book/(author|year)=//article/(author|year)]

but it did not, instead it returned all of the authors. Evidently my predicate is not acting as a filter/qualifier for each element but more of an absolute statement, an evaluation on the entire code. I think that's what is happening anyway. So my question is how can I select an element based on the value of its sibling's child?

asked 44 secs ago

Perrid13

1