Unbreakable space - hard space: possible?

Hi there!
First time on the list. Thanks for the Docbook.

I use SGML Docbook for writing a thesis. 

Is there any way to put "an unbreakable space" ("a hard space") 
between 2 words - not to separate them in two different lines 
in print output (PS, PDF)?

In TeX it's a special '~' character for that, I suppose.

Can I achieve this with Docbook?


Thanks in advance,
Tomasz Nazar

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