On Saturday, Sep 20, 2003, at 23:30 Europe/Rome, Geoff Howard wrote:
Stefano Mazzocchi wrote:
On Saturday, Sep 20, 2003, at 04:34 Europe/Rome, Geoff Howard wrote:Stefano Mazzocchi wrote:pipelines and virtual pipeline components
On Thursday, Sep 18, 2003, at 04:51 Europe/Rome, Geoff Howard wrote:
Stefano Mazzocchi wrote:
I wasn't sure what "uses component" meant functionally.
the blocks declares what component is going to use from that block and will name it. This is the inverse of the cocoon.xroles file but does the same thing, providing a shorthand version of the role identifier in the context of that block.
So, what does a block use from another block if not a component?
Ok. pipelines if a sitemap is declared, and virtual pipeline components
if they are "provide"-ed or exposed.
Hmmm, you made me realize that it's not clear how block can provide virtual pipeline components if a sitemap is not declared.
what do you people think about this?
Also below though they expose files (xsl)...
I'veyep
been thinking that neither file resources or classes would be accessible
directly.
But from the example below there's obviously a shade of meaning in "accessible directly". They are accessible through the block protocol, no?
yes, but never *directly*. see below.
So all that's left is components (either sitemap components or no)? (ah, source resolving through block: protocol?)the blocks carry three things: 1) pipelines (called via the block: protocol) 2) avalon components (accessed via the component manager) 3) pipeline virtual components (declared in your sitemap)
and file resources as below?
as reading pipelines
In the exampleyep
what does the first block (@id="cob:mycompany.com/webmail/1.3.43") use
from cob:mycompany.com/skin aka "external-skin"? I'd guess all that's
left is resolving sources through the block: protocol?So this wouldno.
mean there's a block:external-skin which will probably be some xsl file?
block:external-skin identifies the root of the URI space addressed by that block. You could do things like
block:external-skin:/stylesheets/news2html.xslt
that would return a stylesheet. And so on.
So where is the fact that external-skin can be expected to provide /stylesheets/news2html.xslt recorded? Is it implicit because the resource is actually there in the block?
no, that would create a contract on the file system layout of the block, which might be undesirable (just like the protected/public method you imply below)
Is it only available if a pipeline matches it (eg <map:match pattern="stylesheets/news2html.xslt"><map:read src="stylesheets.news2html.xslt... ).
yep. look that it's entirely possible to do a
<map:match pattern="*">
<map:read src="{1}"/>
</map:match>and forget about it... but later, extending blocks don't necessarely have to follow the same file system approach (they might be already using that directories for something else!) but just have to overload the sitemap.
this gives more flexibility, file system decoupling and explicitness, as in the spirit of the sitemap.
Can it be assumed that any physical file resource in the block can be considered "provided"?
no and should not.
I think there may be a danger here, a parallel to the problem we face when public methods are arbitrarily overridden.
exactly.
The alternative would be some list of publicly available resources available through "block:". I'd guess we'll want to avoid anything other than public or private (declared or not declared) - i.e., no package private, no protected, etc.
that would be a duplication of what the sitemap can do by itself.
Oh, and while we're abusing the java analogy, how many <implements> and <extends> are allowed? I'd think 1 each but I haven't thought it out.
one <extends> and many <implements>, as we follow Java in disallowing multiple inheritance (which would be painful to maintain).
Yes, because the virtual component doesn't have a java classname that can be used to uniquely identify it.If it's a virtual component, would this need to be declared on both the provider and requirer as a component?
...
Sounds good. You snuck in type="hidden-string" by the way which raises the question: what are the allowable values of type? string, integer,KISS
hidden-string, (basic "primitive" values) or complex values like
"phone-number" or "ip address"?FS for now. Let's have String, Number and HiddenString. That should be enough, because the code should do checking at runtime anyway.No need to enumerate specifics now, but the general concept might be good to address. And is it extensible?
Sounds good.
...
Not necessarely. Since cob:mycompany.com/skin/1.2 and cob:mycompany.com/skin/2.3 have different major version numbers, they are declared to be back incompatible. It could be that cob:mycompany.com/skins/corporate/34.3.345, in order to be implement cob:mycompany.com/skin/2.3 had to overload a few URIs from cob:yetanothercompany.com/skins/fancy/1.2.2 whose behavior would not be compliant to implements -> cob:mycompany.com/skin/1.2.The implements uri and the requires uri match up based on versioning rules but are separate for wiring purposes from the @id. But in the scenario: cob:yetanothercompany.com/skins/fancy/1.2.2 implements -> cob:mycompany.com/skin/1.2
cob:mycompany.com/skins/corporate/34.3.345 implements -> cob:mycompany.com/skin/2.3 extends -> cob:yetanothercompany.com/skins/fancy/1.2.2
Does cob:mycompany.com/skins/corporate/34.3.345 also implicitly implement cob:mycompany.com/skin/1.2 because it extends cob:yetanothercompany.com/skins/fancy/1.2.2?
For example, say cob:mycompany.com/skin/1.2 includes /stylesheets/news2html.xslt and /stylesheet/doc2html.xslt.
The first, by default, strips all content that doesn't belong to the news markup language. cob:yetanothercompany.com/skins/fancy/1.2.2 implements this behavior.
Later, a new need is identified (for whatever reason) and the behavior of news2html.xslt is changed so that content in different namespaces is copied over. Clearly, this is a back-incompatible change and this required an increase of the major version number of the URI identifying that behavior (cob:mycompany.com/skin/2.3).
The developers of cob:mycompany.com/skins/corporate/34.3.345 decide to reuse doc2html.xslt (because they know that behavior is still the same) but need to overload news2html.xslt to provide the new behavior that conforms to cob:mycompany.com/skin/2.3.
As you see with this simple (yet very likely to happen) example, the "implements" property is not, generally, transitive.
Gotcha.
What do you mean?Also, does the fact that no component initially defining cob:anothercompany.com/MailRepository/2.0 exists here matter?
Well, we've said it implements this (really set of) block behavior(s) but in the example so far, no block exists with the original "interface" definition. I know there is not a very tight analogy with java interface implementation, but should there be some requirement to have a definition of what a block is implementing when it says it implements it?
no. the java analysis falls short because, for block behaviors, we do not have a way to "describe" this behavior. Eventually, it could be possible to look it up thru the URI (directly, if we move to http: URI or indirectly if we keep cob: URI as we need a lookup machanism), but this is not necessary at this point, it would be only to validate whether or not the block actually *does* implement that behavior, but checking this is simply too hard so we decided to go down the weak typing approach.
If not, whose responsibility is it to ensure that the implementation is complete? The block developer? If so, how do they know when they've done it?
Eh, you are touching a nerve here and, by far, the most critical thing of the whole design.
To draw a parallel, it's weak typing vs. strong typing. Over the years, I came to appreciate both approaches: weak typing for rapid scripting and strong typing for solid foundations.
Where do blocks reside? well, one could say that block reside in the 'solid foundations' realm (if looking from the block developer perspective) or in the rapid scripting (if looking from the block user perspective). Who is right? I don't know.
The only thing I know for sure is that writing a "block behavior descriptor" is such a complex task that it would be foolish to attempt to do so.
Consider the example before: a stylesheet that changes behavior in copying-over or dropping content in another namespace? how do you signal that? how do you test it? an image that is more than 123 pixels wide but less than 134 pixels otherwise the page layout is ruined? how many things would there be to checkout?
As for strong typing advocates: java is not that strongly typed as it seems at first. If you use collections without generics, well, you are on your own. CCE and NPE are avoided only with *your* care during development.
In short, I think block behavior validation will simply work on its own, by comparing to a reference implementation of that behavior. That behavior URI might point to a document that explains what services are provided and what not, but this is not to be machine digestable, but simply a for-humans descriptions of what the blocks do.
True, it's entirely possible to incrementally create an ontology of block operations and use DAML+OIL software to perform validation and truth analysis, but given the amount of people that volunteer their brain to do that truth analysis on their own, why should we substitute "real intelligence" with "artificial" one?
With this and the above questions I'm trying to get at where the hiddenGreat. This is useful to me as well, as it stress-tests the design. keep up the nice thinking.
contracts are.
...
Ok, I've wiki'd the latest with my proposal about @id and @block included.ok, sounds good to me. anybody else?
I suspect that either others are not really paying attention anymore because of the length of the thread, or the relative "unsexyness" of this first step.
I think a followup email pointing to the wiki results so far and asking for comment would be a good step here RSN. I suppose this doesn't need a vote (?) but that would be another way to ensure someone will peek their head in.
In the meantime I am happy to play the Meno to your Socrates,
:-)
I agree on the general unsexyness of these things, but only because we don't have anything working.
As soon as things start to work, I expect tons of comments, mostly of things that were already said before ;-) but, hey, that's life.
-- Stefano.
