What is XQuery

XQuery is a query language designed for querying and extracting data from XML documents. It is a powerful and expressive language that allows you to perform complex operations on XML data, including querying, filtering, transforming, and aggregating data from XML sources. XQuery is a W3C standard and is part of the family of XML-related standards, along with XML, XPath, and XSLT.

Key Features of XQuery:

1. XML-Focused: XQuery is specifically designed for working with XML data. It is aware of the hierarchical structure of XML documents and allows you to navigate and query XML data directly.
2. XPath Integration: XQuery integrates XPath expressions for addressing and selecting nodes in XML documents. XPath is used as the basis for the location path expressions in XQuery.
3. FLWOR Expressions: FLWOR (For-Let-Where-Order by-Return) expressions are a powerful construct in XQuery, allowing you to perform iterations, filtering, sorting, and returning results. FLWOR expressions are similar to SQL queries, making XQuery expressive and easy to use.
4. Data Types: XQuery supports a wide range of data types, including strings, numbers, booleans, dates, and durations. It also allows the creation of user-defined data types.
5. Namespaces: XQuery fully supports XML namespaces, allowing you to work with XML documents containing elements and attributes from different namespaces.
6. Grouping and Aggregation: XQuery supports grouping and aggregation functions, allowing you to group data based on specific criteria and perform calculations on grouped data.
7. Extensibility: XQuery is extensible, meaning you can define your own functions and operators to enhance its capabilities based on specific requirements.
8. Module System: XQuery has a modular design, allowing you to organize your queries into reusable modules, making your code more manageable and maintainable.
9. Integration with XSLT: XQuery and XSLT are complementary technologies. While XSLT is primarily used for transforming XML documents, XQuery is used for querying and extracting data from XML documents. The two languages can be used together in XML processing pipelines.

XQuery Example:

let $books := doc("books.xml")//book
where $books/price > 30
order by $books/title
return
  <book>
    <title>{$books/title}</title>
    <author>{$books/author}</author>
    <price>{$books/price}</price>
  </book>

In this XQuery example, we load an XML document from the file “books.xml” and filter the book elements with a price greater than 30. We then sort the filtered books by title and return a new XML structure containing the title, author, and price of each selected book.

XQuery is widely used in various domains, including data integration, content management systems, web services, and XML database applications, wherever querying and processing XML data are required. Its expressive syntax and XML-centric features make it a versatile language for XML data manipulation and retrieval.