- John has a garden behind his house. Three quarters of the garden is plain green, presumably grass.
- There is an object in the garden visible from the satellite picture. It looks as if it might be a rusty lawnmower. It has been there all winter.
- It is nearly Spring. John might need a new lawnmower soon.
Note that many of the observations are uncertain. The grass might be artificial, and the rusty object might be an exercise bike. The garden supply company might wish to purchase higher-definition images, or invest in better image recognition software to improve the interpretation of the raw images, but this investment would be wasted unless there was a good chance of increasing the number of lawnmowers sold.
In any case, there are lots of other things that might influence John's purchasing decision. John might have another lawnmower in the shed. He might be too busy to mow his garden, so he pays Harry (who brings his own mower). Meanwhile, John might want to buy a new lawnmower as a house-warming present for his daughter.
From both a business perspective and an engineering perspective, we can construct effective and profitable systems without bothering our heads whether the rusty lawnmower really exists, or whether it is just an unreliable interpretation of pixels on a satellite image. And what about John's desire for a new lawnmower? Does this really exist, or is this just a bit of hopeful speculation by the marketing department?
So I want to build models that include things like probability, intentionality and the future. Do these things "exist" in the real world, or are they some kind of construction? Rick Murphy explores the question of Representation and Realism in the context of the Semantic Web. In a later post on Signs of the Singularity, he argues that because the semantic web follows Tarski, model theory implies realism. "The relation between a model and the world may be only one of approximation, but without realism, technological utopianism quickly precedes to simulacra and simulation."
I don't think it's as simple as all that. And if it was, would it matter?
See follow-up post on Analyzing the Rusty Lawnmower.