Thanks! I'll save this talk as a reference.
Really my question was focused on possibile risks or safety issues; it's so strange that a database (since I see wikisource as a database) is mainly indexed, from the user's point of view, on a variable field as title of the page, that I suspected some serious safety issue. And - strangely enough - id is not shown at all into pages, nor there's any magic word or other user friendly method to get it.
From a practical point of view, many from wikisource page titles are very
long, often they use non-ascii characters and mixtures of capitalized and not capitalized characters, they can't be used as they are as local file names... in brief, I feel all this stuff almost as annoying as the apostophes used in wiki markup for bold and italic. ;-)
Alex