real world columns: interruptions

A friend of mine was queuing for the check-out in a supermarket recently when there was a fire alarm and everyone had to be evacuated. For my friend this was not a problem, faced with a further twenty minute wait to pay, she was glad to leave the basket there and get out. Which in itself is interesting since it was a way of having the whole shopping experience without actually buying anything.

However, for other shoppers the experience was a bit different since some were in the middle of the actual purchase, they had just handed over cash and were waiting for change, or they had a bag of things but hadn’t yet got their receipt. The end-to-end purchase transaction was suddenly being split in the middle. Should they leave the goods they had just bought there in the shop, should the security guards challenge everybody that was leaving with goods, would it be a good chance to grab a few bottles of scotch and saunter out with the other shoppers?

This interruption of transactions is not always a vital scenario to design for. When it comes to sorting out what happens to the people at the till when there is a fire in the shop it is a miniscule number of cases and in each case the transaction is small (on a company perspective). They are certainly not going to re-engineer the transaction system and protocols to completely prevent errors in such a small number of cases.

However, there are situations where transactions can be interrupted more easily and where the transaction is worth a lot more than a basket of groceries. Consider the signing of documents by several parties to purchase a company. Although things can always go wrong in the transaction (person A signs five documents then person B has a heart attack after they have signed the first two of them) the error that has to be prevented is the intentional one. Person A signs a document saying that all their stock in the company is to be transferred to B. Person B grabs it and runs out of the door without signing their document and without making ten million pounds over to person A.

Lawyers who arrange such big deals put a lot of effort into ensuring that what happens is ‘watertight’ or legally perfect at each point in the proceedings. So that even if the transaction is interrupted for whatever reason, the state of affairs at that moment is complete, legal, and cannot be abused in any way. Legal transactions are interesting because it is human-human interaction that is being carried out according to a very strict set of rules and protocols.

Another bizarre illustration of transaction design in human-human legal interaction is the serving of a notice or a court order to someone in Britain. This is in effect just giving someone a formal document. But what if they don’t receive it through the post – how can you prove that they have seen it? If you call at their house and actually hand it to them then they really have received it, but what if they don’t want to participate in the transaction and put their hands in their pockets when you try and hand them the document? The legal answer is that it is sufficient to touch the person with the document! (Check out: www.tbtv.co.uk/stb_social_faqs.asp).

Managing transactions and coping gracefully with interruptions is also important in the way that pieces of technology communicate with one another. If you accidentally hit the ‘mail merge’ button on a contact database and the printer starts printing thousands of letters, you want to quickly be able to pull the plug and stop the transaction. What you also want is the transaction to be ended in a coherent way so that the printer will behave sensibly after you put the plug back in. There are certain situations with technology, especially those where you are messing with the more deep-seated bits of programming, where the transactions are very delicate indeed. Installing a new BIOS on an older laptop for example. You have to have a power lead and a full battery and if you interrupt it mid-way you can end up having to bin it because it gets into a state that it is impossible to get it out of.

The early Apple Macs almost got into problems with interrupted transactions with floppy disk ejection. You put a floppy in and the icon appears on the desktop. Instead of doing ‘put away’ or dragging the icon to the trash can you do ‘eject’. The floppy pops out and the icon is left on the desktop but is grayed out. You drop the floppy in the nearest river and next day, on the desktop, you try and clean up by dragging the grayed out icon to the trash can. To dispose of the icon properly the Mac asks you to insert the floppy back into the drive, and - hey presto! - you are stuck in an impossible transition. But those people at Apple obviously thought about this and if you cancel the operation with the apple and period keys, the demand for the lost floppy disappears along with the grayed out icon!

The legal problems described above also arise with the combination of the two; interruptions involving machines and humans. One country had problems with its first ATMs because the legal framework to support them had not been put in place. Legal framework? I hear you ask. Well if I request a hundred dollars from the ATM and then don’t actually take it out of the machine but just leave it there, can I legally be said to have taken delivery of the cash? The early machines would offer the money and if the money wasn’t taken from the slot the machine would suck it back in again and register the transaction as null and void. Which was fine until someone discovered that you could slip one of the middle bills out without the ATM being aware of it!