Open Stack

On 11/27/2013 02:03 PM, Adrian Otto wrote:
> Jay,
>
> On Nov 27, 2013, at 10:36 AM, Jay Pipes <jaypipes at gmail.com> wrote:
>
>> On 11/27/2013 06:23 AM, Tom Deckers (tdeckers) wrote:
>>> I understand the an Assembly can be a larger group of
>>> components. However, those together exist to provide a capability
>>> which we want to capture in some catalog so the capability
>>> becomes discoverable. I'm not sure how the 'listing' mechanism
>>> works out in practice.  If this can be used in an enterprise
>>> ecosystem to discover services then that's fine.  We should
>>> capture a work item flesh out discoverability of both
>>> Applications and Assemblies.  I make that distinction because
>>> both scenarios should be provided. As a service consumer, I
>>> should be able to look at the 'Applications' listed in the
>>> Openstack environment and provision them.  In that case, we
>>> should also support flavors of the service.  Depending on the
>>> consumer-provider relationship, we might want to provide
>>> different configuratons of the same Application. (e.g.
>>> gold-silver-bronze tiering).  I believe this is covered by the
>>> 'listing' you mentioned. Once deployed, there should also be a
>>> mechanism to discover the deployed assemblies.  One example of
>>> such deployed Assembly is a persistence service that can in its
>>> turn be used as a Service in another Assembly.  The specific
>>> details of the capability provided by the Assembly needs to be
>>> discoverable in order to allow successful auto-wiring (I've seen
>>> a comment about this elsewhere in the project - I believe in
>>> last meeting).
>>
>> Another thought around the naming of "Assembly"... there's no
>> reason why the API cannot just ditch the entire notion of an
>> assembly, and just use "Component" in a self-referential way.
>>
>> In other words, an Application (or whatever is agree on for that
>> resource name) contains one or more Components. Components may
>> further be composed of one or more (sub)Components, which
>> themselves may be composed of further (sub)Components.
>>
>> That way you keep the notion of a Component as generic and
>> encompassing as possible and allow for an unlimited generic
>> hierarchy of Component resources to comprise an Application.
>
> As currently proposed, an Assembly (a top level grouping of
> Components) requires only one Component, but may contain many. The
> question is whether we should even have an Assembly. I admit that
> Assembly is a new term, and therefore requires definition,
> explanation, and examples. However, I think eliminating it and just
> using Components is getting a bit too abstract, and requires a bit
> too much explanation.
>
> I consider this subject analogous to the fundamentals concepts of
> Chemistry. Imagine trying to describe a molecule by only using the
> concept of an atom. Each atom can be different, and have more or less
> electrons etc. But if we did not have the concept of a molecule (a
> top level grouping of atoms), and tried to explain them as atoms
> contained within other atoms, Chemistry would get harder to teach.
>
> We want this API to be understandable to Application Developers. I am
> afraid of simplifying matters too much, and making things a bit too
> abstract.

Understood, but I actually think that the Component inside Component 
approach would work quite well with a simple "component type" attribute 
of the Component resource.

In your particle physics example, it would be the equivalent of saying 
that an Atom is composed of subatomic particles, with those subatomic 
particles having different types (hadrons, baryons, mesons, etc) and 
those subatomic particles being composed of zero or more subatomic 
particles of various types (neutrons, protons, fermions, bosons, etc).

In fact, particle physics has the concept of elementary particles -- 
those particles whose composition is unknown -- and composite particles 
-- those particles that are composed of other particles. The congruence 
between the taxonomy of particles and what I'm proposing is actually 
remarkable :)

Elementary particle is like a Component with no sub Components
Composite particle is like a Component with sub Components.
Each particle has a type, and each Component would also have a type.

Other possibility:

Call an Assembly exactly what it is: ComponentGroup

Best,
-jay