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From Jeremy Quinn <jer...@media.demon.co.uk>
Subject Re: [RT] Link Rewriting
Date Tue, 29 Apr 2003 20:58:35 GMT

On Tuesday, April 29, 2003, at 07:50 AM, Jeff Turner wrote:

> On Mon, Apr 28, 2003 at 03:16:34PM +0100, Jeremy Quinn wrote:
>> Hi All
>>
>> Welcome to my first RT!
>>
>> Sorry to start on a negative note, but IMHO, the current scheme for
>> LinkRewriting just does not make sense for dynamic sites.
>>
>> What the current scheme allows is for authors to use a simple set of
>> declarators for defining links, which are then translated into actual
>> URLs, (and in the samples) mapped directly to filespace (etc.).
>
> Yes.  <link href="site:foo">, where 'foo' is your declarator, and the
> link is translated into the actual URL <a href="foo.html">.
>
> So LinkRewriterTransformer does the mapping:
>
> declarator -> *.html, *.pdf etc (URL)
>
> However, that was only half of the original Linkmap vision :)  I think
> you're asking for the other half, which is declarator -> SystemID
> (*.xml).

Ah Ha!

> See the original linkmap RT:
>
> http://marc.theaimsgroup.com/?l=forrest-dev&m=103444028129281&w=2

OK, this is interesting!

> The declarator -> SystemID mapping in that RT was declared in a 
> site.xml
> file:
>
> <site dir="./content/xdocs">
>   <index file="index.xml"/>
>   <dreams file="dreams.xml"/>
>   <faq file="faq.xml">
>     <how_can_I_help xpath="/faqs/faq/question[@id='how_can_I_help']">
>     <building_own_website 
> xpath="/faqs/faq/question[@id='own_website']"/>
>     ....
> </site>
>
> That is functionally equivalent to the XML in your post quoted below.

Yes, I think so.

> In the linkmap RT, I envisioned a Source that accepts a 'declarator' 
> as a
> @src, and emits XML from that declarator's SystemID.  Your idea of 
> using
> input modules with dynamic inputs, {site:{1}}, is a nicer 
> implementation
> than what I had in mind.
>
>> What I believe a LinkRewriting infrastructure should offer is rather
>> different.
>>
>> A URL is a CONTRACT.
>>
>> Cocoon's sitemap is excellent at disconnecting any direct relationship
>> between URL and resource ID/Path (SystemID). Allowing the
>> re-implementation of storage schema independently of URL contract.
>>
>> What I feel makes more sense is this:
>>
>> 	URL == permanent contract == authoring link != SystemID
>>
>> What this means is, authors should write links using a static absolute
>> URL, the same one as the public contract for that particular piece of
>> information.
>>
>> When that URL is accessed, it should be mapped to a SystemID, allowing
>> independent re-implementation of the storage layer.
>
> So we have URLs everywhere, and in the sitemap we do a lookup on a
> linkmap to determine the actual source?  This kind of thing:
>
> <map:match pattern="*.html">
>   <map:generate src="content/xdocs/{linkmap:{1}}"/>
>   ...
> </map:match>

Yes, using nested input modules to modify the XPath expression to 
handle the different LinkMap formats people would want. For instance, I 
prefer to use some thing close to XLink.

>
>> If this is to be handled by an input module accessing a linkmap 
>> (before
>> Generation, rather than during Transformation), but requires that
>> dynamic sitemap URL fragments can be passed to input modules (as they
>> cannot currently).
>>
>>  see: 
>> <http://marc.theaimsgroup.com/?l=xml-cocoon-dev&m=104895916400307>
>>
>> The transformation stage is then merely one of relativising author's
>> URLs.
>
> But that isn't the only use of link rewriting :)  The original idea was
> that <link href="site:index"> could be translated into:
>
>  - <a href="index.html"> if linked to from a *.html file
>  - <a href="index.pdf"> if linked to from a *.pdf file
>  - <a href="#index"> if linked to from an aggregate HTML
>  - <fo:basic-link internal-destination="index"> if linked to from an
>    aggregate PDF
>  - ....
>
> This is the value of the descriptor -> URL mapping.

Yes, this is not something I had dealt with yet.
Very nice!

>
> Actually, Forrest doesn't yet support this neat stuff yet, but that was
> the original idea and it will be implemented as soon as enough users
> complain about broken 'site:' links in their PDFs :o)
>
> Anyway, point is, there's two sites to 'linkmapping', and both are
> valuable.
>
>> Most of what I have described here, is how most people use Cocoon.
>> What is new here is the use of a LinkMap at the Generation stage to
>> de-couple URL from SystemID in a totally arbitrary way. A version of
>> the LinkMap idea that makes sense for Dynamic sites. This is what
>> requires changes to the way we are able to use input modules, as input
>> modules would provide a much cleaner path to handle this rather than
>> Transforming a generated LinkMap into CInclude tags to get the 
>> content.
>>
>>
>> Does this make any sense to anybody?
>
> Perfectly :)
>
> Now let me play devils advocate..
>
> If we assume the user knows how to edit the sitemap, is there any real
> benefit in this extra level of declarator -> *.xml indirection?  What's
> the difference between editing a sitemap.xmap, and editing a 
> linkmap.xml
> file?  Both just map declarators to SystemIds.

I think Nicola Ken said it better than I could in his previous reply 
....


Many thanks for the feedback

regards Jeremy


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