Keyword or keyphrase in tagging system?

Question

In term of effectively categorizing web content, I am wondering what are the pros and cons between keyword (a.k.a tag, e.g, google-app-engine) and keyphrase (e.g. google app engine).

I know that delicious.com and this site are using keyword as a tag. But why don't they use keyphrase instead? If they use keyword, then it may cause certain inconsistences (e.g., app-engine and appengine, web-2.0 and web2.0). I wonder if I choose using keyphrase as a tag, then it will become much better. I have no clue why those two major sites don't work as the way I thought. Are there any cons of using keyphrase? Please point it out to me.

Answer 1

The obvious difference:

• If you use keywords-like-this, then a list of multiple keywords can be space-separated.

• If you allow keyphrases like this with spaces in, you can't space-separate the keyphrases.

That means you either introduce some other separator character that your users need to learn about, or you have a much more complex user interface for editing tags.

(The inconsistency problem you mention will happen either way: app engine / appengine vs. app-engine / appengine.)