XML Query Language

Extensible Markup Language(XML): Introduction Creating XML Documents XML style Sheet Hyperlinks in XML Document Object Model XML Query Language

XML Query Languages help in extracting and processing data stored in XML documents.

i) XML documents are structured hierarchically like a tree, where elements are arranged as

parent–child nodes. XPath is a query language used to navigate through this tree structure

and select specific parts (nodes) of the XML document.

Purpose of XPath

• To locate elements, attributes, text, or parts of XML documents.

• Used heavily in:

o XSLT transformations

o Web APIs (such as SOAP)

o XML-based data processing tools

o Automation and testing tools (e.g., Selenium Web Driver)

How XPath Works

XPath uses path-like syntax, similar to file paths, to navigate XML elements.

Example XML

<Library>

<Book id="B101">

<Title>Data Structures</Title>

<Author>Ravi Kumar</Author>

<Price>500</Price>

</Book>

</Library>

Basic XPath Syntax and Selectors

XPath Expression         Meaning / What it Selects

/Library               Selects the root element <Library>

/Library/Book                Selects the <Book> element inside <Library>

//Book                 Selects all Book elements in the entire document

/Library/Book/Title            Selects the <Title> element

//Book[@id='B101']           Selects Book element with id attribute equals B101

//Price/text()                  Extracts the text content inside <Price>

Node Types XPath Can Select

• Element nodes → <Book>

• Attribute nodes → @id

• Text nodes → text inside tags

• Parent / child / sibling relationships

Advantages of XPath

• Works with both simple and complex XML structures.

• Highly efficient for searching data in XML trees.

• Foundation for higher-level query tools like XQuery.

XQUERY

While XPath helps in navigation, XQuery helps in querying and retrieving data, similar to

SQL for databases.

Purpose of XQuery

• Extract data from XML documents.

• Perform filtering, sorting, grouping, and joining operations.

Used in:

o Native XML Databases (e.g., BaseX, eXist-db)

o Enterprise Integration Systems

o Web Services

o Data Analytics Platforms

XQuery vs SQL

Feature         SQL                       XQuery

Operates on             Tables (rows & columns) XML trees (nodes, elements)

Data Structure   Relational                 Hierarchical

Output           Tabular data                   XML, HTML, or text

FLWOR Expression Structure (Core of XQuery)

FLWOR →     FOR, LET, WHERE, ORDER BY, RETURN

It resembles natural programming & SQL-like query processing.

Part          Meaning                          Purpose

FOR          Iterates over a sequence of XML nodes       Acts like a loop

LET            Assigns values to variables                 Useful for optimization

WHERE    Applies conditions / filters                  Similar to SQL WHERE

ORDER BY     Sorts the results                        Ascending / Descending

RETURN Defines what output should be generated Final structured result

Example XQuery Using FLWOR

XML Input

<Library>

<Book>

<Title>AI Foundations</Title>

<Author>Dr. Rao</Author>

<Price>750</Price>

</Book>

<Book>

<Title>Machine Learning</Title>

<Author>Prof. Anita</Author>

<Price>900</Price>

</Book>

</Library>

XQuery

for $b in /Library/Book

where $b/Price > 800

order by $b/Title

return

<ExpensiveBook>

<Name>{ $b/Title/text() }</Name>

<Cost>{ $b/Price/text() }</Cost>

</ExpensiveBook>

Output

<ExpensiveBook>

<Name>Machine Learning</Name>

<Cost>900</Cost>

</ExpensiveBook>

Where XML Queries Are Used (Real World Applications)

Area                           Usage

Business Data Analytics   Extracting structured information from XML-based data warehouses.

Web Services (SOAP/REST)         Many APIs return data in XML → XPath/XQuery helps parse it.

Database Systems                   Querying Native XML Databases and XML-enabled RDBMS like

Oracle / SQL Server.

Configuration and Enterprise    Many enterprise software store config/settings in XML which Systems                    are queried using XPath/XQuery.