Week 41 of 2009

I'm not often pleasantly surprised by Microsoft but I was when I discovered Microsoft Security Essentials. It provides totally free virus protection on XP and Vista. Now, I'm not a big fan of giant companies squishing little ones by dumping free software into the marketplace. However, the existing virus protection vendors have been pissing me off for years. They are almost impossible to uninstall and the last two I used were constantly reminding me to renew their subscription even though I had lots of time left on my existing subscription. The first time this happened a few years ago, I renewed by mistake thinking my time was up. It wasn't, I still had 6 months left on the old subscription. Anyway, I hope they all disappear into oblivion now!

With regards to OOA Tool, the week has progressed very slowing with my attention moving from one area to the next trying to tie off loose ends. I didn't manage to finish any bigger items so there isn't much to talk about here!

Perhaps I could talk about the confusing world of events and signals. Shlaer-Mellor users don't need to worry about signals at all. However, Shlaer-Mellor users may be confused by internal and external events which should really be called internal and external event generations (as opposed to invocations) since they relate to the generation of events rather than the specification of events. The OOA Dictionary retains the original names even though they are a little confusing since they appear frequently in the existing literature. However, internal and external process invocations (which are a similar concept) are not shortened to internal and external processes since the latter does not appear in the existing literature.

Executable UML users do have to worry about events and signals and to confuse matters further, xtUML [xtUML02] and xUML [xUML04] use the terms differently. Now, UML2 [UMLManual05] uses the term event only when discussing state models. The term signal is applied to classes carrying information for asynchronous communications. The more general term message is normally used when discussing communications in general. This contrasts with Shlaer-Mellor which uses the term event in all of these situations. Now xtUML uses the term event correctly according to UML2, although signal event might be more appropriate but unnecessary since call events and change events aren't supported. I'm skipping over time events here even though delayed events (a similar but different concept) is supported in Shlaer-Mellor and Executable UML. However, xtUML uses the term signal for generated events (i.e. internal and external events in Shlaer-Mellor) which isn't really correct. Executable UML doesn't allow classes containing event information to be defined. This is a tricky area but using the term signal here is probably less confusing than using event. On the other hand, xUML uses the term signal almost exclusively which also isn't correct. OOA Tool always uses xtUML conventions but Executable UML users should note that there are small differences between xtUML and xUML.

A final note for anyone here in the UK. I watched Micro Men the other day on iPlayer seeing how Clive Sinclair and Chris Curry kick started the micro computer industry here in the UK. Unfortunately, both of their companies failed. Very sad for the UK. I still have a Sinclair QL in good condition although I haven't had it out of the box in the last 10 years! I don't know what happened to my Sinclair Spectrum but that was my very first computer. I never did buy a BBC Micro but I remember using one briefly in college.