Recently while I was editing the categories and tags of my blog posts, I suddenly had a realization about what is the purpose of both.
Once I state it, it’s going to sound too obvious. And I am not claiming that I must be the first one to think about this. But hey, this is my blog, right?
This is what I think. Categories are used for top down search that leads to my article. The tags are used for bottom up search leading to my article. Categories are more abstract grouping terms. Tags are concrete entities that appear in the blog post.
So an article about recent a particular event in US politics that involved President Obama, the category will be politics. But the tag will be Obama, President, USA and so on. If we were arranging the movie DVDs, then the genre of the movie, like horror, comedy, etc. will be category and the actors, director, etc. will be tags.
When the search engine looks for a articles related to certain term, I am sure they begin the filtering with tags. The ancient search engines purely weighed articles based on number of times the tags appear in the article. Thus in the days before Google, if you wanted your article about rockets to come first in search, all you had to make sure was the word rocket came a few thousand times in your metatags and content.
With google and onwards, the search engine somehow figure out how relevant the tags are to main article. So in short, they calculate “category”. If you have given the correct category, it will help a lot at this stage. Because your blogging site will list your blog in correct category, thus agreeing with the search engine, and thus increasing your chances of being seen by random search engine audience.
Many times people just add same words in category and tags. It leads to less efficient search for the whole blogosphere. By doing that, they are temporarily advancing their blog in the short run, but killing the overall blogging activity in the long run.