Extracting useful data from HTML pages with XQuery

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Learn XQUERY and EveryThing Xquery
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In this video we are demonstrating how to build a mobile solution that is built on top of legacy data by extracting that data from an ...

Extracting useful data from HTML pages using XQuery can be accomplished by leveraging libraries and tools that support parsing HTML. Below is a guide on how to do this effectively.

Overview

  1. Understand the HTML Structure: Familiarize yourself with the HTML document you want to query.
  2. Use an XQuery Processor: Choose an XQuery processor that supports HTML parsing (e.g., BaseX, eXist-db).
  3. Write XQuery to Extract Data: Formulate queries to extract the desired information.

Step-by-Step Guide

Step 1: Set Up Your Environment

  1. Choose an XQuery Processor: Install a suitable processor like BaseX or eXist-db.
  2. Load HTML Document: Ensure your HTML document is accessible, either from a local file or a URL.

Step 2: Load HTML in XQuery

When using BaseX, you can load HTML documents directly. Here's how you can do it:

xquery
let $html := doc("path/to/your/file.html")

Step 3: Writing XQuery to Extract Data

Assuming you have an HTML document structured as follows:

html
<html>
<head><title>Sample Page</title></head>
<body>
    <h1>Welcome to the Sample Page</h1>
    <div class="content">
        <p>Here is some useful information.</p>
        <ul>
            <li>Item 1</li>
            <li>Item 2</li>
            <li>Item 3</li>
        </ul>
    </div>
</body>
</html>

html 2

You can write XQuery to extract specific data, such as the title and list items.

Step 4: Example XQuery Queries

1. Extract the Title of the Page

xquery
let $html := doc("path/to/your/file.html")
return $html/html/head/title/text()

2. Extract All List Items

xquery
let $html := doc("path/to/your/file.html")
for $item in $html//li
return <item>{$item/text()}</item>

3. Extract Paragraph Text

xquery
let $html := doc("path/to/your/file.html")
return $html//div[@class='content']/p/text()

Step 5: Running Your XQuery

  1. Open your XQuery processor (e.g., BaseX).
  2. Enter and execute your queries in the query editor.
  3. Review the output in the results pane.

Additional Considerations

  • HTML Parsing Libraries: Some XQuery processors may require additional libraries or extensions for robust HTML parsing. Check documentation for support.
  • XPath Expressions: Use XPath expressions to navigate through the HTML structure effectively.
  • Handling Dynamic Content: For pages generated dynamically (e.g., JavaScript), consider using a headless browser approach to fetch the complete HTML before processing.

Conclusion

Using XQuery to extract data from HTML pages is a powerful way to gather and manipulate information from web content. By following the steps outlined above, you can efficiently query and process HTML documents. If you have specific examples or scenarios in mind, feel free to ask!