Interpreting Search Results

Question

Hi all,

I am tasked with writing a program that, given a search term and the HTML source of a page representing search results of some unknown search engine (it can really be anything, a blog, a shop, Google, eBay, ...), needs to build a data structure of the results containing "what's in the results": a title for earch result, the "details" link, the position within the results etc. It is not known whether the results page contains any of the data at all, and whether there are any search results. The goal is to feed the data structure into another program that extracts meaning.

What I am looking for is not BeautifulSoup or a RegExp but rather some clever ideas or algorithms on how to interpret the HTML source. What do I do to find out what part of the page constitutes a single result item? How do I filter the markup noise to extract the important bits? What would you do? Pointers to fields of research covering what I try to to are aly greatly appreciated.

Thanks, Simon

Answer 1

I doubt that there exist a silver-bullet algorithm that without any training will just work on any arbitrary search query output.

However, this task can be solved and is actually solved in many applications, but with different approach. First you have to define general structure of single search result item based on what you actually going to do with it (it could be name, date, link, description snippet, etc.), and then write number of html parsers that will extract necessary necessary fields from search result output of particular web sites.

I know it is not super sexy solution, but it probably the only one that works. And it is not rocket science. Writing parsers is actually extremly simple, you can make dozen per day. If you will look into html source of search result, you will notice that output results are typically very structured and marked with specific div sections or class atributes, so it is very easy to find it in the document. You dont have even use any complicated HTML parsing library for that, something grep-like will be enough.

For example, on this particular page your question starts with <div class="post-text"> and ends with </div>. Everything in between is actually a post text with some HTML formatting that you may want to remove along with extra spaces and "\n". And this <div class="post-text"> appears on the page only once.

Once you go at large scale with your retrieval applicaiton, you will find out that there is not that big variety of different search engines on different sites, and you will be able to re-use already created parsers for sties using similar search engines.

The only thing you have to remember is built-in self-testing. Sites tend to upgrade and change design from time to time. If your application is going to live for some time, you will need to include into your parsers some logic that will check validity of their results and notify you every time search output has changed and is not compatible anymore with your parser. Then you will have to modify particular parser or write new one.

Hope this helps.