Data layer should handle that. But, where that data comes from should be of no relevance to anything outside of the datalayer. Read up on Domain Driven Design. http://www.infoq.com/minibooks/domain-driven-design-quickly

>Ok, this sound nice (and familiar to me) but who/where does what 'he should not care about' ?
>(because that is almost all I care about! )
>
>According to terminology I would suspect that this is happening somewhere in datalayer
>or this is as well done at entity level ? (in som foundation classes of NET framework)
>
>What are the possibilities there in terms of programming / modelling / datamunging.
>For instance I want to control contingency scenarios. (Multiple users accesing the same records etc)
>
>Pls don't tell me that this is blackboxed somewhere and customisable as easy as BIOS... {g}