Keyword based searching definitely has limitations. If a search keyword does not appear in the context of any "good" documents you're searching for, the search engine will not return any "good" results. In the example above, a search for "bull terrier" and imgcolor=red only returned 1/20 "good" result. And "bull terrier" has high semantic relevance. This is because the authors of the "good" documents I was looking for (e.g. the Target dog) rarely use "bull terrier" in the document context.

Plus keyword based search engines can be easily hacked to associate garbage with certain keywords.

I guess a color parameter would be considered semantic search? Here's a cool link (new today) about google integrating more semantic search features. http://www.pcworld.com/businesscenter/article/161890/semanti...