Q:

Barkeeper, or bartender? How to address them?

I dunno if I'm right about the meaning of these words.
What do you call the person who owns a bar, or a pub? And the person who serves you with 
drinks at the counter? [As the two may not be identical ...]
What to yell [though maybe it is not that polite, but who cares when a bit tipsy anyway] to address either of 'em? :-)

A:

In England, in my 10 years running pubs, and another 10 years working in them, I have encountered many terms for the various people you might find working in a pub:

Licensee: holder of the licence to sell alcohol.  Often the owner of the business (not necessarily the owner of the premises), sometimes a manager.  In some cases there are joint licensees. You would not address someone as "Hi, licensee" though.  However, the Police (or similar) may ask to speak to the licensee, or licence-holder.  Since the Licensing Act 2004, they may now ask for the DPS, which stands for Designated Premises Supervisor, who may be the licensee or a duty manager.
Landlord/Landlady: Generally the person, or one of the persons, who runs the pub.  This is usually used in terms of independent pubs, in which the owner is a single-site operator.  In this case it is generally also the licensee and his wife/husband/partner who hold these titles.  You might say "Good evening, landlord/lady", as a regular customer, but would not use "Hey, landlord" to get their attention.
Publican: Similar to the above but refers to the profession of running a pub, and is how I described myself to people when they asked what I do for a living.
Barman/barmaid: A person employed by the landlord/manager to work behind the bar.  In the UK you would not say "Hey, barman" or "Hey, barmaid" to attract attention.  Nor would you say "Good evening, barman/barmaid", except in a rather ironic way to a member of staff that you knew well.
Bartender/server: Relatively modern additions to pub vocabulary in the UK, mostly used in job adverts to avoid breaching the employment discrimination laws.
Barkeep(er): Totally unused here.
Gaffer: what many of my regular customers called me.  Even though I was the landlord and licensee, owner of the business, tenant of the premises, and often the barman/cook/cellarman/gardener/woodcutter/cleaner etc.

Finally, to address the matter of what to yell.  Yelling to get attention will bump you down the queue in most UK pubs, not up. Whistling and finger-clicking will have a similar effect.  A simple "Excuse me", or a small upwards nod of the head, or just holding (NOT waving) some money in front of you and looking hopeful is often the best technique. A bounce of the eyebrows while you're within the server's line of sight will remind them that you have not yet been served.
On a topical note, there is some excellent light-hearted advice for those who have forgotten that a pub is for life, not just for Christmas. These rules are well-distributed around the web, so I'ev reproduced them in full here: 

It’s that festive time of year when decent, honest boozers are plagued
  by non-drinkers. And not real non-drinkers, not people who don’t ever
  drink, they’re fine. We’re talking about people who don’t go near a
  pub for 11 months out of the year!!
Here’s a guide on how to not be quite so awful
DO NOT APPROACH THE BAR UNTIL YOU KNOW WHAT YOU WANT The bar is NOT
  the place to think or choose or decide.
DON’T START DRINKING AT 4pm You’re NOT a drinker. We haven’t seen you
  all year. You’re an amateur, so don’t start out with a marathon.
YOU ARE IN A ROUND I don’t care who you’re with, how many of you there
  are or how well you know them. You are in a round with all the people
  you came in with. That’s how it works.
KNOW WHERE YOU ARE Look around you. What kind of drinking
  establishment are you in? Is it a pub or a bar?
We’re a pub adorned with wood furnishings and hand-pulls, so stop
  trying to get the landlord to make that s***ty cocktail you saw on Sex
  And The City
HOT GIRLS GET SERVED FIRST Welcome to Western Civilization.
iPHONE ETTIQUETTE Our music has been specifically selected to offend
  the least amount of people and I like it. If you want anything else,
  then you want to be at a club or a gig.
ATTRACTING ATTENTION Newsflash: You are NOT next. You might have been
  in the bar queue longer than anybody else, but that doesn’t mean
  you’re next.
Do you know why? Because there are no ‘Official Rules Of Queueing At
  The Bar.’ The bartender is 100% in charge of who is next. So do not
  p*** them off.
PREFERENTIAL TREATMENT If an old bloke sat at the bar gets served
  before you do, and the bartender knows him by name and even seems to
  know what he’s drinking before he orders it – that’s Bob. Bob drinks
  here all the time. Bob drinks here five times a week, every week.
  Bob’s custom pays the bills.
Bob and the other Regulars keep the pub open eleven months of the year
  whilst you’re having dinner parties and bulk-buying booze from the
  supermarket. Yes, they get preferential treatment. Accept it.
TIME IS TIME (sometimes) Pubs don’t stop serving because they hate you
  (that’s a lie, sometimes they do) or because it’s funny or because
  they get bored of selling beer.
It’s a legal requirement for them to stop serving at a designated
  time. Once Time is called, they are legally unable to sell anymore
  beer.
You cannot cajole them into selling more, because it’s a legal
  requirement. You cannot bribe them into selling more, either with the
  promise of drinks or money, because it’s a legal requirement.

