SoaIsNightSky is a conceptual analogy for ServiceOrientedArchitecture.  Obtaining data from a service is likened to harnessing light from distant stars of varying distance.  Just as light from distant stars may take many years to arrive, and therefore reflects a time in the distant past, the data from a service may not reflect the current conditions at the source.  Furthermore, the "light" (data) gathered for a local service is used to produce more "light" (data) for consumption at a distant requester.  This may raise concurrency issues, especially as services are supposedly autonomous.  

For example, a service may issue a status of "Approved" for a given customer.  The "Approved" status may pass through the bowels of several other services before being exposed to a consumer.  By the time the consumer receives that information, the given customer's status may no longer be "Approved," causing subsequent actions to fail or resulting in erroneous conditions.  Obviously, such problems may be encountered in virtually any architecture (traditional ClientServer architecture may be subject to this as well) but may be exacerbated in SOA due to the particularly asynchronous nature of services.  This leads some to say SoaIsNightSky.

This notion originated in PatHelland's blog at http://blogs.msdn.com/pathelland/archive/2004/03/18/91825.aspx

The author of the "night sky" metaphor for ServiceOrientedArchitecture got involved in an extended discussion on the nature of services at http://blogs.msdn.com/pathelland/archive/2004/03/22/94000.aspx
* "[the other person believes we] need concurrency control (optimistic or pessimistic) to connect the services.  I argue that this is how services are different than components.  This is an in-depth discussion about the lack of shared transactions across service boundaries in SOA."
* At the end of that post, another contributor stated that "When designing a service interface you should always be prepared to handle concurrency issues."

The author closed the debate with these statements:
* ''In summary, computing in SOA is like the night sky.  We act on our local information and the information we know about what the other services used to look like.  While this is a different computing model, it is the only possible computing model in a loosely-coupled and distributed world.''
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A related article entitled "Data on the Outside vs Data on the Inside" can be found at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/dataoutsideinside.asp
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See WhatIsSoa SoaAndLooseCoupling
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CategorySoa