Re: Warning of major NHS IT overspend

[Dave Howe <[EMAIL PROTECTED]>]

Roger Hird wrote:
> Phase simply two proved too difficult, none of it ever happened, and for
> years afterwards the central databases continued in use, accessed through
> windows on the PCs emulating dumb ICL terminals.  Ex colleagues I've
> spoken to still think that trying to merge data kept on a range of local
> systems, even if theoretically possible, is extremely difficult and
> unreliable.
Actually, it can be quite simple and reliable - how simple and reliable 
depends on how often the distributed data needs to be updated, how 
conflicting updates are resolved, and how often the schema which 
indicates what is stored where is changed.
DNS (as used by the internet) is a good example of a distributed system 
- the schema sometimes changes, you can have multiple copies and cached 
results stored all over the internet - but because only a single copy is 
permitted to be changed (and the official copies and cached copies take 
their cue from that) the changes ripple cleanly across the internet only 
rarely causing conflicts.