On Fri, Dec 6, 2013 at 10:56 PM, Russ Nelson <nel...@crynwr.com> wrote:
> Andy Street writes: > > Was the building first opened on that date? or was it when the pub began > > trading? > > My main use of start_date and end_date would be for railroads, and > even that isn't sufficient, because some railroads were built, used, > ripped up, and laid down again, and then ripped up again. How would > that be tagged? start_date, end_date, start_date_1, end_date_1? Head > asplode! > The first obvious solution to that would be to create two entities in the database which "just happen" to coincide, and which should probably be linked somehow. One entity would be for the land, the physical ground underlying the railway, and would represent the land easement for the railroad, the physical location. The other entity would be for the actual tracks in the ground, the rails and ties and switches and the like, setting on top of and supported by the physical land easement. It would make sense for the entity representing the tracks in the ground to link back to the entity representing the physical ground, the land easement. (The tracks cannot be there, or at least not usefully there, without the land easement for them to rest on.) It might or might not make sense to link the other way; in the example you suggest, should the land easement continue to link to tracks which have been ripped up and are not physically present any more? (Does or should an entity in such a status remain in the database?) I'm certainly not going to say this is and must be the correct way to handle this situation; it's first quick thoughts concerning the issue and how to resolve it and as such might be horribly incorrect given more knowledge of the database and all. But, at least to this naive and ignorant person, it's not obviously and completely and immediately apparent to be wrong, at least at a first surface look. Joseph
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