2008-12-30

Domain driven design, Test driven design

I was just reading through the VBUG events list when I came across an event entitled "Domain driven design approach, using unit testing".

"Sounds interesting!" I thought to myself, I hope I can make it! As I started to read it I thought it looked familiar. At that point I realised it was me doing the talk! So hopefully I will be able to make it :-)

The posting is here. If you come along make sure you say "Hello".

2008-12-16

Computer music

You may already know that I used to own a Commodore 64, and (as is nearly everyone else who ever owned one) I am still very passionate about the music people used to produce on it.

The question "Which was your favourite Commodore 64 tune" is a very hard one to answer as there are so many good ones out there, and people tend to go for the same short list "Delta", "Sanxion", etc.

However, recently I was creating some ambient background music for a presentation video. It started off a bit like a Jarre tune, but as I started to add in the percussion (for which I used samples of car doors slamming) it started to remind me of a tune from an old C64 game; "Tetris".

After downloading it and listening to it endlessly over and over as I write code I have come to a conclusion; TETRIS is my favourite C64 tune! It is just so unique, and unlike many other C64 tunes it hasn't aged, and doesn't actually sound that much like a C64 tune at all! Whenever I listen to it I feel like I am in the former USSR, building something out of strangely shaped bricks :-)

There's a (large) Mp3 of the tune here if you are interested.

Well done Wally Beben, you have in my opinion created a classic, and I will undoubtedly continue to enjoy it for many years to come. Actually, I am going to do a remix of it too, I hope he wont mind :-)

2008-12-15

FireBird - Did it burn me?

This morning I spent an hour on the phone to Microsoft support. I tried to log into my machine only to see the error message

The user profile service failed the logon.
User profile cannot be loaded.

The guy on the phone got me to put my Vista install DVD into the drive, boot from that, go to system-recovery, and revert to a restore point. Worked nicely.

The thing is, why did this happen? The only thing I can think of is Firebird server. I installed it on Sunday to get an old app to run (installed as app, not service). I didn't install the control panel plugin due to a warning on the site telling me not to install it on Vista or it will trash my Control Panel.

I suppose the warning about the control panel should have been enough to put me off. Still, it works now. I just wont be installing it again, at least for some time.

2008-12-05

The importance of clarity

I wrote and now maintain a Pocket PC app for Imperial Tobacco (yes, despite supporting the ban on smoking in public places). It is important that the date/time on the PPC is accurate so part of the business flow is to get the user to check the date/time immediately after they log in.

Despite this step we were getting invalid dates back from their collected data, in all cases it was always one day ahead of the correct time. We have recently introduced various additional common sense checks such as "You have missed a working day, are you sure?" etc, but the change that will have the biggest affect is the one that was the smallest to change.

When the user enters the current date/time if it is less than the last known date/time on the server (sent in their database of work to do) I showed a message saying it was incorrect. The message read

"The date you have entered is invalid"

At this point the user looks at the date they have entered, thinks "but the date is right!", they click it forward a day and the PPC accepts it, so they continue with their work. Because I used the word "date" the user was blinkered to the value in the date, and didn't even bother looking at the time they had entered. The message now reads

"The date/time you have entered is invalid"

Hopefully this will be a bigger clue :-)

Northern lights

For my 35th birthday my wife bought us two tickets to take a flight up north to see the aurora borealis with Aurora Flights. Here is a photo of the view from our window. As you can see we didn't manage to see much at all. In fact, despite sitting at the window directly over the wing we couldn't actually see the wing (except for the flashing light on its tip).

There was a small clear area at the top, but due to the thickness of the window frame we couldn't get our heads high enough to look down at the lights, only up at the stars (which were great). As a consequence our entire view of the northern lights was merely a dull band of murky green fog. At one point I got excited because I thought I could see some vertical structure in the lights, unfortunately I soon realised it was merely the dirty window as it moved whenever I moved my head.

I strongly suspect that the only good way to see the lights is to stand on the floor and look up. Most definitely one of the most disappointing experiences of my entire life.

2008-12-01

The ubiquitous language

One of the most important things to do when designing a system for a customer is to to try create a common business language between you and the people who understand the problem domain. A lack of what is known as "the ubiquitous language" can result in misunderstandings and a failed project.

I had a real life experience of a ubiquitious language failure yesterday. My brother went to the shop to buy some credit for his phone and offered to take my children with him to buy sweets. When they got back my son asked me

"How come uncle Stephen was able to buy credit for his phone?"

When I asked what he was talking about he described the sign on the wall in the shop, it read

"Please do not ask for credit as refusal often offends"