Advanced SID: Logical and Physical Resources

The SID, like many other ways of modelling a Telecoms enterprise or any form of ICT distinguishes between a Logical and a Physical Resource. Anyone in IT thinks that they know what that means… We all know about ‘virtual devices’, virtual memory, virtual machines, and virtual private networks…

So if a Physical Resource is a handset or a switch, then a logical resource is, well, something like a VPN!

Well, “Yes and No” – certainly the concept of Logical Resource could cover the idea of VPN. But there are other things, more useful things to the Telecoms industry that Virtual Resource can cover.

We know that a physical resource has a physical location, has dimensions like weight, height, colour, and even things like smell, and taste (though mobile phones don’t smell or taste of much). These resources, or assets, have a value, are sold and supported by a party and have to be managed in an inventory.

I know some of you are ready with the next answer…

A Logical Resource is something conceptual that has no physical representation, but still is a resource that has to be tracked. Things like MSISDN, IMSI, IMEI and PUKs are all Logical Resources and the SID certainly means those to be included within the definition of Logical Resources.

Yes, that is very true and these things are very important forms of Logical Resources, but still there are others, and to appreciate the full beauty and extensibility of the SID we must look further.

I want to digress for a moment before I expand on the meaning of Logical Resource and what it covers.

Many years ago, I came across the “Duck Test”. It is a simple rule that states something along the lines of

“If it looks like a duck,
walks like a duck and
quacks like a duck….
Then it is a duck”

One problem we’ve got as data modellers is that if we come from a physical data modelling background as opposed to an logical data modelling (oh, there’s that word again) then we are always looking for things that make one thing different from another. With the SID, and Enterprise Modelling in general we should always be looking for things that make them similar – or identical to other things – the broad rather than the narrow view, and I find the “Duck Test” very useful in this area.

So what else is like a logical resource? – That looks like a logical resource, walks like a logical resource and quacks like a logical resource?

Come on, I gave a big clue just now when talking about physical and LOGICAL database designs…

What about software? It can’t be measured, weighed, it has no colour, smell or taste, but it still exits. It fulfils the criteria of being a logical resource. We certainly keep inventories of our software, it has a value and has to be purchased and maintained. It can be installed into other Resources (Logical and Physical) and can even have a physical location – my copy of Microsoft Word is installed on my p.c. that is at the moment on a train in France (but that is another story).

Software is a Logical Resource.

So what?

Well there are two really useful things we can do with this idea.

Firstly it starts to help us understand RFSs. After all what does software do, but provide services?

And secondly how is software made? How is it written and designed, and how is that represented in the SID? Something for you to think about!