Develop an efficient web crawling and data extraction system, utilizing advanced algorithms to systematically search the vast expanse of the internet for specific keywords and phrases. The overarching goal is to meticulously organize the gleaned information into a meticulously structured Excel document, thereby creating a valuable dataset poised for optimal utilization in machine learning applications and analyses.

1. Develop a web crawling script to navigate through the identified websites.
2. Implement logic to search for and extract information related to the specified keywords and phrases.
3. Handle cases of dynamic content and implement necessary delays to avoid overloading the target websites.
4. Clean and preprocess the extracted data to ensure consistency and accuracy.
5. Transform the data into a structured format suitable for machine learning applications.
6. Handle missing or irrelevant information appropriately.
7. Develop a script to organize the extracted data into an Excel spreadsheet.
8. Ensure that the Excel document follows a predefined structure and is easily understandable by machine learning algorithms.
9. Include relevant metadata and annotations for better context.
10. Implement error handling mechanisms to deal with potential issues during the web crawling process.
11. Validate the correctness of the extracted data against the defined requirements.
12. Test the system on a diverse set of websites to ensure its robustness and reliability.
13. Optimize the crawling process for efficiency and speed.
14. Consider the scalability of the system to handle a large volume of data.

Deliverables

1. Web Crawling Script: Develop a Python script using Beautiful Soup, Scrapy, or Selenium to crawl the web and extract data based on specified keywords and phrases.
2. Structured Data Extraction: Implement logic within the script to accurately extract relevant information from web pages, ensuring consistency and accuracy in data extraction.
3. Data Cleaning and Transformation Module: Create a module within the script to clean and preprocess the extracted data, handling issues such as missing values, irrelevant information, and data inconsistencies.
4. Excel Document Generation: Develop a script to organize the cleaned and transformed data into a structured Excel document, adhering to predefined formatting and structure requirements suitable for machine learning applications.
5. Documentation: Provide comprehensive documentation for the web crawling script, including clear instructions for usage, explanation of code logic, and any dependencies required for execution.
6. Testing and Validation Report: Conduct thorough testing of the web crawling and data extraction process, and generate a report documenting the validation results, including accuracy and completeness metrics.
7. Ethical Compliance Documentation: Document adherence to ethical standards and legal considerations regarding web scraping, including measures taken to ensure compliance with terms of service of target websites.
8. Scalability Optimization Recommendations: Provide recommendations for optimizing the web crawling system for scalability, including strategies for handling large volumes of data efficiently and minimizing resource utilization.
9. Presentation or Demonstration: Prepare a presentation or demonstration showcasing the functionality and effectiveness of the developed web crawling system, highlighting key features, challenges overcome, and potential applications.
10. Feedback and Iteration Plan: Develop a plan for incorporating feedback from stakeholders and implementing iterative improvements to the web crawling system, ensuring ongoing enhancement and refinement.