My view is that the dash is used to separate a phrase or part of the sentence from the rest of the sencence, almost the same way as a comma or semicolon would operate. The Dash operates almost as a pause; but short of that denoted by a full stop. An example of the use of a Dash could be:
We could finally see the waters of the sea - the beauty of its aquamarine waters having always facinated me - and knew that it would take our bus another half to reach the port, were the boat was waiting for us.
The point I would like to reconfirm is as follows: Whereas a hyphen (example: Vice-President) which separates two parts of a hyphenated word, should not have a space on either side of it, a Dash, as in the example above, should have a space on either side of it.
Could you please let me know if this is true.
There are actually three marks: the hyphen, the en-dash (which used to be as wide as an "n" in typesetting), and the em-dash.
The hyphen never has spaces. mother-in-law, well-paid job.
The en-dash is used like the word "to" or "through" in giving a range. I can't make an en-dash on my laptop, so I will use a hyphen, but it's something like "October 11-13 at the Topsham Fairgrounds." You will see it both with and without spaces. You will use this less often, and no one will question the meaning.
The em-dash is the one you're talking about. It's a multi-purpose punctuation mark (and one I use too often in my writing). Some style guides say that you should leave a space on either side, but others say to NOT leave the spaces. My company's style is to not leave the space, but my personal style (when writing e-mail, for example, not in a brochure, which follows company style) is to leave the space.
If your system clearly differentiates between the two marks -- that is, if the em-dash is CLEARLY longer than the hyphen -- then you can choose to not have the spaces. My concern would be that if they look alike, you've made it harder for your reader to figure out what you mean. You can use the double hyphen, as I have. In that case, leave the spaces or don't -- but just be consistent in how you use them.