[NeXus-tech] quick thought on application definitions

[Pete R. Jemian]

[one connecting thought missing from previous ... insert after the URL]

Reading this page further, it describes how an interface is used.  A 
class that implements this interface must provide the methods defined in 
the interface.  "Interfaces form a contract between the class and the 
outside world, and this contract is enforced at build time by the 
compiler. If your class claims to implement an interface, all methods 
defined by that interface must appear in its source code before the 
class will successfully compile."

[then, after Mark's quote]

It's the contract that makes these two notions similar.



On 11/2/2010 2:06 PM, Pete R. Jemian wrote:
>
> Recent workshop at DESY has me thinking and that is dangerous ...
>
> This might be content for the "manual" so excuse me while I think out loud.
>
> Conceptually, application definitions are similar to the Java notion of
> the interface. In Java, "an interface is a group of related methods with
> empty bodies."
> (http://download.oracle.com/javase/tutorial/java/concepts/interface.html)
>
> As Mark K says, an application definition forms a contract between the
> provider and the consumer that certain named data items are guaranteed
> to be available.
>
> To me then, a scientific technique might store all data items within an
> application definition. However, we expect that a beamline will store
> its information in a component tree based on the base classes and then
> provide one or more subentry application definitions with links from the
> expected names of that application definition to the actual data in the
> component tree. Different instruments will likely use different links to
> meet the same application definition. In some cases, it may still be
> necessary to define reductions of data from the component tree in the
> application definition but that seems more of a detail than a rule.
>
> Pete
>
>
>

-- 
----------------------------------------------------------
  Pete R. Jemian, Ph.D.                <jemian at anl.gov>
  Beam line Controls and Data Acquisition, Group Leader
  Advanced Photon Source,   Argonne National Laboratory
  Argonne, IL  60439                   630 - 252 - 3189
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     Education is the one thing for which people
        are willing to pay yet not receive.
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