COP 4020 XQuery XML Query

XQuery: XML Query Language

XQuery (XML Query Language) is designed to query and manipulate XML data. It provides a powerful way to navigate, transform, and extract information from XML documents.

Key Features of XQuery

1. Data Retrieval: XQuery allows you to extract specific data from XML documents using a structured query syntax.
2. Data Manipulation: You can update, insert, or delete nodes in XML documents.
3. Integration with XPath: XQuery uses XPath expressions to navigate through XML trees.
4. Support for Functions: It includes built-in functions for string manipulation, date handling, and more.

Basic Syntax

An XQuery expression typically follows this structure:

for $variable in $sequence
let $anotherVariable := expression
where condition
order by $sortExpression
return expression

Components

• for: Iterates over a sequence of items.
• let: Binds values to variables.
• where: Filters results based on a condition.
• order by: Sorts the results.
• return: Specifies what to output.

Example XML Document

Consider the following XML document:

<library>
    <book id="1">
        <title>Learning XQuery</title>
        <author>John Doe</author>
        <price>29.99</price>
    </book>
    <book id="2">
        <title>Advanced XQuery</title>
        <author>Jane Smith</author>
        <price>39.99</price>
    </book>
</library>

Example XQuery Expressions

1. Retrieve All Book Titles

To get a list of all book titles:

for $book in doc("library.xml")/library/book
return $book/title

2. Filter Books by Price

To find books priced over 30:

for $book in doc("library.xml")/library/book
where $book/price > 30
return <result>
          <title>{$book/title/text()}</title>
          <author>{$book/author/text()}</author>
       </result>

3. Sort Books by Title

To sort books alphabetically by title:

for $book in doc("library.xml")/library/book
order by $book/title
return <result>
          <title>{$book/title/text()}</title>
          <author>{$book/author/text()}</author>
       </result>

4. Create a New XML Structure

To create a new XML catalog from the existing data:

<catalog>
  {
    for $book in doc("library.xml")/library/book
    return <item>
              <title>{$book/title/text()}</title>
              <author>{$book/author/text()}</author>
              <price>{$book/price/text()}</price>
           </item>
  }
</catalog>

Conclusion

XQuery is a powerful language for querying and manipulating XML data. With its rich syntax and capabilities, it allows developers to efficiently extract and transform XML information. If you have specific requirements or need further examples, feel free to ask!