Terms

[Ray Plante]

Tony et al,

On Thu, 9 Dec 2004, Tony Linde wrote:
> One of the problems we have is that we're all using different terms for the
> same things (or vice versa). Can someone (Roy?) provide us with a reasonable
> glossary of entities that we need to look at and quickie definitions. 

Please recall that the RM document defines a number of terms that are 
relevant to this discussion.  

> I've left out 'resource' deliberately - it is a somewhat loaded term. And
> I've tried to keep to the higher level entities at this stage.

The definition provided by the RM is intended to clarify this and allow us 
to use the term without fear.  

   "A resource is a general term referring to a VO element that can be 
    described in terms of who curates or maintains it and which can be 
    given a name and a unique identifier.  Just about anything can be a 
    resource: it can be an abstract idea, such as sky coverage or an 
    instrumental setup, or it can be fairly concrete, like an organization 
    or a data collection.  This definition is consistent with its use in 
    the general Web community as anything that has an identityâ
    (Berners-Lee 1998, IETF RFC2396).  We expand on this definition by 
    saying that it is also describable."

The definition is deliberately broad ("Just about anything can be a 
resource") allowing us wide latitude for how we populate our registries 
(e.g. coarse-grained vs. fine-grained).  The RM document further refines 
the definition of a resource by identifying the core metadata that 
can/must be included to describe a resource.  

To further refine what is and isn't a resource is to impose one's own 
additional constraints on how one perceives the VO.  That is okay, but the 
RM standard implies that those constraints need not be universally 
accepted.  More to the point, you should not expect others be aware what 
additional meaning you have imposed unless you explicitly say so.

As for the other terms, consider:

>  data centre (or center)

RM does not define this term; instead it talks of organizations and 
providers:

   organization:  a "specific type of resource that brings people together 
     to pursue participation in VO applications."
   provider:  "an organization that makes data and/or services available 
     to users over the network."

Here's an other one that's important:

   Publisher:  "An entity responsible for making the resource available"

I think it is fair to say that "data center" unnecessarily implies more 
than these other terms from the RM.  

>  service

>From the RM:
   "any VO resource that can be invoked by the user to perform some action 
    on their behalf."

>  interface

The RM does not define this directly; however, but the implied definition 
based on the definition of "Inteface metadata" is that an interface is the 
mechanism for accessing a service--namely, "the inputs and the outputs".  
A tighter definition would be better.  

Definitions for some others are included in the VOResource metadata 
schemas (and thus are less definitive).

>  data collection

from VODataService-v0.5.xsd: 
     "A logical grouping of data which, in general, is composed of one 
      or more accessible datasets."

>  dataset (which I think is just my term for data collection)

from VODataService-v0.5.xsd, in an annotation to the definition of 
DataCollection:
     "A dataset is a collection of digitally-encoded data ... that 
      is normally accessible as a single unit, e.g. a file."

cheers,
Ray