ikiwiki/doc/forum/an_alternative_approach_to_structured_data.mdwn

## First Pass

Looking at the discussion about [[todo/structured_page_data]], it looks a bit like folks are bogged down in figuring out what *markup* to use for structured page data, something I doubt that people will really agree on.  And thus, little progress is made.

I propose that, rather than worry about what the data looks like, that we take a similar approach
to the way Revision Control Systems are used in ikiwiki: a front-end + back-end approach.
The front-end would be a common interface, where queries are made about the structured data,
and there would be any number of back-ends, which could use whatever markup or format that they desired.

To that purpose, I've written the [[plugins/contrib/field]] plugin for a possible front-end.
I called it "field" because each page could be considered a "record" where one could request the values of "fields" of that record.
The idea is that back-end plugins would register functions which can be called when the value of a field is desired.

This is gone into in more depth on the plugin page itself, but I would appreciate feedback and improvements on the approach.
I think it could be really powerful and useful, especially if it becomes part of ikiwiki proper.

--[[KathrynAndersen]]

> It looks like an interesting idea.  I don't have time right now to look at it in depth, but it looks interesting. -- [[Will]]

> I agree such a separation makes some sense. But note that the discussion on [[todo/structured_page_data]]
> talks about associating data types with fields for a good reason: It's hard to later develop a good UI for
> querying or modifying a page's data if all the data has an implicit type "string". --[[Joey]] 

## Second Pass

I have written additional plugins which integrate with the [[plugins/contrib/field]] plugin to both set and get structured page data.

* [[plugins/contrib/getfield]] - query field values inside a page using {{$*fieldname*}} markup
* [[plugins/contrib/ftemplate]] - like [[plugins/template]] but uses "field" data as well as passed-in data
* [[plugins/contrib/ymlfront]] - looks for YAML-format data at the front of a page; this is just one possible back-end for the structured data

--[[KathrynAndersen]]

> I'm not an IkiWiki committer ([[Joey]] is the only one I think)
> but I really like the look of this scheme. In particular,
> having `getfield` interop with `field` without being *part of*
> `field` makes me happy, since I'm not very keen on `getfield`'s
> syntax (i.e. "ugh, yet another mini-markup-language without a
> proper escaping mechanism"), but this way people can experiment
> with different syntaxes while keeping `field` for the
> behind-the-scenes bits.
>
>> I've started using `field` on a private site and it's working
>> well for me; I'll try to do some code review on its
>> [[plugins/contrib/field/discussion]] page. --s
>
> My [[plugins/contrib/album]] plugin could benefit from
> integration with `field` for photos' captions and so on,
> probably... I'll try to work on that at some point.
>
> [[plugins/contrib/report]] may be doing too much, though:
> it seems to be an variation on `\[[inline archive="yes"]]`,
> with an enhanced version of sorting, a mini version of
> [[todo/wikitrails]], and some other misc. I suspect it could
> usefully be divided up into discrete features? One good way
> to do that might be to shuffle bits of its functionality into
> the IkiWiki distribution and/or separate plugins, until there's
> nothing left in `report` itself and it can just go away.
>
> --[[smcv]]