Opacity calumny

[Frank McCabe <frank.mccabe@us.fujitsu.com>]

I read the revised section on services. And an issue that made me  
uneasy before has resurfaced -- about opacity.

I think that the opacity/transparency dimension is not a good basis  
for distinguishing services. I am aware of the intuition: that  
somehow when you use a service you should not have to worry about the  
implementation. But what does it mean to say: "the implementation is  
hidden from the service consumer"? If the service is to add lists of  
numbers then its implementation is hidden provided numbers are added  
up correctly. (I.e., we should not care about whether its in C++ or  
C#; multi-threaded or federated).

But, some services are explicitly about implementation issues:  
security services, workload distribution services, java remote  
execution engine services etc. etc. I.e., it is of the essence that  
to use a Java remote execution service, you have to send it a java  
class to execute. In that sense, the implementation is critical.

A clearer distinction is public/private. A service is characterized  
by a public description of its functionality. The public description  
should be sufficient to be able to successfully interact with the  
service; and no additional information should be required.

Frank