XQuery is a programming language used for querying and transforming XML data, enabling extraction and combination of XML documents. It supports features like variables, loops, conditionals, and functions, making it versatile for data manipulation tasks. XPath, a language for selecting nodes in XML documents, works with XQuery to efficiently query XML structures using various path expressions.

1. Xpath & Xquery
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2. XQuery
● XQuery is an active programming language, which is used to
interact with XML data groups.
● It is primarily used to extract, transform, and combine XML
documents.
● It can read and write the data in the database which is used in
software and services integration for making analysis reports.
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3. Example 1: Basic Query
An XML document with information
about books:
<library>
<book>
<title>XML for Beginners</title>
<author>John Doe</author>
<price>19.99</price>
</book>
<book>
<title>Advanced XML</title>
<author>Jane Smith</author>
<price>29.99</price>
</book>
</library>
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4. To extract all book titles using XQuery, you would write:
for $book in doc("library.xml")//book
return $book/title
In this example:
● doc("library.xml") refers to an XML document.
● //book is an XPath expression that selects all <book> elements in the
document.
● The for clause iterates over each <book> element and returns the title
of each book.
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5. Example 2: Filtering and Returning Data
To extract book titles where the price is greater than 20:
for $book in doc("library.xml")//book
where $book/price > 20
return $book/title
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6. Example 3: Using Variables
Variables can be defined within an XQuery:
let $minPrice := 20
for $book in doc("library.xml")//book
where $book/price > $minPrice
return $book/title
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7. XQuery Components:
● Variables (let): Used to assign values that can be reused.
● For loops: Iterate over sequences of data.
● Conditionals (if/then/else): Allow for conditional branching in the query.
● Functions: XQuery supports defining functions for reusability.
● XPath Expressions: Used for selecting nodes or parts of the XML
document.
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8. XQuery Example Use Cases:
1. Data Extraction: Extracting specific data from XML-based files.
2. Transformation: Transforming XML documents into other formats (e.g.,
JSON or HTML).
3. Data Aggregation: Aggregating XML data, such as counting elements or
summing up values.
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9. Xpath
● XPath is an XML method language which is applied for node selection in
XML dataset using queries.
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10. XPath Syntax
1. Absolute Path:
An absolute path starts from the root node of the XML document.
/library/book/title
This selects all <title> elements that are children of <book>, which is a child of
<library>. The path starts from the root node (denoted by /).
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11. 2. Relative Path:
A relative path starts from the current node and doesn’t necessarily start from the
root.
book/title
This would select <title> elements that are children of <book>, but it starts the
search from the current context node.
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12. 3. / and //:
● / selects from the root of the document.
● // selects nodes at any level, not necessarily directly under the current node.
//book
This selects all <book> elements in the document, regardless of their position in
the tree.
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13. 4. @ for Attributes:
You can select attributes using the @ symbol.
//book/@id
This selects the id attribute of all <book> elements in the document.
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14. 5. Using Predicates (Conditions):
Predicates are used to filter nodes based on certain conditions. These are
enclosed in square brackets [].
//book[price > 20]
This selects all <book> elements where the <price> child element has a value
greater than 20.
● We can also use predicates to select specific occurrences of elements:
//book[2]
This selects the second <book> element.
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15. XPath Examples:
1. Select all books:
//book
2. Select the title of the second book:
//book[2]/title
3. Select the price of books where the price is greater than 20:
//book[price > 20]/price
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16. 4. Select the id attribute of the first book:
//book[1]/@id
5. Select the text content of all titles:
//book/title/text()
6. Select all books that are written by "John Doe":
//book[author = "John Doe"]
7. Select the author of the first book:
//book[1]/author
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