Xpath & Xquery in XML documents for retreving data

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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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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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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Example 2: Filtering and Returning Data
To extract book titles where the price is greater than 20:
where $book/price > 20
return $book/title
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Example 3: Using Variables
Variables can be defined within an XQuery:
let $minPrice := 20
where $book/price > $minPrice
return $book/title
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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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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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Xpath
● XPath is an XML method language which is applied for node selection in
XML dataset using queries.
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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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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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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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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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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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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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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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Xpath & Xquery in XML documents for retreving data

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Xpath & Xquery in XML documents for retreving data