What is a ticket?

Sounds like a stupid question, I know, but most of the unfixable problems I've run into with all the other ticketing systems I've worked with have come from failing to answer this question.

Consider the most basic, primitive ticketing system imaginable: a book of raffle tickets. There are two basic interactions with this "system":

• As a customer, I go up to the box office and hand over some money, and in return receive a piece of paper. 
• As a customer, I go up to the entrance to the venue, and hand over my piece of paper to an usher, who tears it in half and allows me through the door. 

In this example, a single, humble piece of paper is fulfilling two entirely distinct functions:

• Firstly, that of stock control. The main purpose of a ticketing system is to prevent you from overselling the event, from breaching the fire regulations, from selling the same seat twice. If there are no raffle tickets left in the book, you cannot sell any more. 
• Secondly, access control. The main purpose of a ticketing system is to prevent people who have not paid the fee from attending the event (“event” here may include performance, train journey, museum exhibit, etc).

They're both the "main" purpose, because they're both encapsulated in the idea of "selling tickets"; it's the idea of a ticket that's confused between these two functions.

When all you've got is a hammer, everything looks like a nail... and right up to the invention of the computerised box office system, the convenience of using the same tokens that you use to keep track of sales volumes as the token that lets you through the door was irresistible.And so the terminology and business process of box officer were based around these bits of paper, and the first box office systems, specified by box office managers, embedded these ideas in their architecture.

Trouble is, this all gets terribly confusing when you start selling - and then delivering - tickets on the internet. An efficient ticketing system for the internet age must be clear on when you're dealing with "the right to occupy a seat" - the stock control, when you're dealing with "the unique serial number or bar code that you assign to the ticket so you can check that it's valid" - which I will hereafter refer to as "the access control token", and when you're dealing with the physical medium that's carrying the access control token - perhaps a piece of card from a BOCA printer, perhaps a sheet of paper from the home inkject printer with a barcode on it, perhaps an RFID card or a mobile phone or any other device - which I no longer have a good name for, because "ticket" is a much to loaded term to use, and "print out" doesn't cover the act of "loading some data onto a smart card".