如何从FLOWR for XQuery的上下文中打开BaseX数据库？

Question

如何将上下文设置为特定数据库，然后在FLOWR中引用该数据库？

PS C:\Users\thufir\Desktop\basex>
PS C:\Users\thufir\Desktop\basex>
PS C:\Users\thufir\Desktop\basex> basex .\openDB.xq
<book category="web">
  <title lang="en">XQuery Kick Start</title>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
  <year>2003</year>
  <price>49.99</price>
</book>
PS C:\Users\thufir\Desktop\basex>
PS C:\Users\thufir\Desktop\basex> type .\openDB.xq
let $db := db:open("books")
for $item in $db
return $item/bookstore/book[3]
PS C:\Users\thufir\Desktop\basex>
PS C:\Users\thufir\Desktop\basex> basex db.xq
Stopped at C:/Users/thufir/Desktop/basex/db.xq, 1/21:
[XPST0003] Expecting ':=', found 's'.
PS C:\Users\thufir\Desktop\basex>
PS C:\Users\thufir\Desktop\basex> type .\db.xq
declare context items := db:open("books")

for $ctx in .

return $ctx

PS C:\Users\thufir\Desktop\basex>
PS C:\Users\thufir\Desktop\basex>

另请参阅：

how to return the third book from this bookstore using FLOWR in XQuery?

我想这样指定数据库：

how to specify a BaseX database from a FLOWR xquery?

，但在XQuery本身的上下文中明确。