2024-02-09T21:21:18
Status: #moc
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Links: [[home]] | [[Technology]] | [[Software Development]] | [[Standards]] | [[XML]] | [[XPath]] | [[XQuery]] | [[XML Schema]]
# XQuery
XQuery, which stands for [[XML]] Query, is a powerful language designed to query XML data. Developed by the World Wide Web Consortium (W3C), XQuery provides means to extract and manipulate data from XML documents. Its functionality is akin to what SQL offers for relational databases but tailored to the hierarchical nature of XML data.
![[afalk42_An_illustration_for_a_knowledge_base_article_on_XQuery__6a57fcb3-c8a2-4466-8eb8-7b6b425ca973.png]]
## Key Features of XQuery
- **Hierarchical Data Processing**: XQuery is adept at navigating and processing the inherent hierarchical structure of XML data.
- **Expressive Querying**: With XQuery, users can perform complex queries and join data from multiple XML sources.
- **XML Data Manipulation**: Beyond querying, XQuery allows for the construction and transformation of XML data.
- **Function Support**: XQuery supports user-defined functions, enhancing its versatility and power.
- **FLWOR Expressions**: These expressions (For, Let, Where, Order by, Return) provide a flexible and powerful way to query and manipulate data.
## Basic Syntax and Concepts
### 1. **XQuery FLWOR Expression**
A fundamental construct in XQuery is the FLWOR expression, which stands for For, Let, Where, Order by, and Return. This is a powerful way to iterate over sequences, filter, sort, and return results.
```xquery
for $x in doc("mydata.xml")//item
where $x/price > 20
order by $x/name
return $x
```
This simple query looks for `<item>` elements within `mydata.xml` where the price is greater than 20, orders them by name, and returns the result.
### 2. **XPath Within XQuery**
XQuery is actually a superset of [[XPath]], so you can use standard XPath expressions to navigate through elements and attributes in an XML document. For example, `//book/title` fetches the title elements of all book elements regardless of their position in the document.
### 3. **Constructing XML**
XQuery can also construct [[XML]], and it can be done using direct element and attribute constructors (i.e. plain XML that is embedded in the XQuery code) as well as computed element and attribute constructors. For instance:
```xquery
let $book := element book {
attribute price { 13.29 },
<title>XQuery Essentials</title>,
<author>John Doe</author>
}
return $book
```
This constructs an XML fragment and returns it as the result.
## Use Cases
- **Data Integration**: Pulling data together from multiple XML sources.
- **Data Analysis**: Running complex queries on XML data for reporting and analysis.
- **Web Services**: XQuery can be used in the implementation of web services that return XML data.
## [XQuery Tools](https://www.altova.com/xquery-tools)
- [XQuery Editor](https://www.altova.com/xmlspy-xml-editor/xquery-editor)
- [XQuery Debugger](https://www.altova.com/xquery-tools#xquery-debugger)
- [XQuery Back-mapping](https://www.altova.com/xmlspy-xml-editor#xslt_back-mapping)
## XQuery Training & Reference
- [XQuery 3.1 Online Training](https://www.altova.com/training/xquery3)
- [XPath/XQuery 3.1 Functions and Operators Reference](https://www.altova.com/xpath-xquery-reference)
## Conclusion
XQuery stands as a robust and versatile language designed to query, construct, and manipulate XML data efficiently. Its ability to precisely navigate and process hierarchical data structures makes it a vital tool for anyone working with XML databases. As XML continues to be a prevalent format for data exchange and configuration, understanding and leveraging XQuery can significantly enhance data processing and analysis tasks in complex XML data environments.