microformats2-parsing-brainstorming

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Revision as of 12:43, 4 October 2011 by Tantek (talk | contribs) (→‎Parsing Microformats 2.0 Syntax: Extraction vs. Interpretation: clarifications on some implicit assumptions, gathering material for a microformats-2-parsing-faq)
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Author: Ben Ward

Microformats 2 proposes a new, all encompassing syntax modification of prefixes that will allow microformats to be parsed from pages by processors without prior knowledge of a vocabulary. The core components of this model are quite simple, are quite simple to implement, but there are a number of conflicts that emerge with the functionality of existing microformats parsers that need to be handled. This page documents a proposed model to separate these concerns clearly in a way that can be applied to the documentation of generic microformats parsing rules, and the documentation of individual vocabularies.

Parsing Microformats 2.0 Syntax: Extraction vs. Interpretation

A microformats ‘1.0’ parser performs the following function:

  • Given a piece of HTML content, discover a known microformat, extract it, apply various extraction patterns based upon the HTML mark-up used (e.g. include pattern, abbr patterns, date-time patterns, value-title pattern), apply various content optimisations where applicable, and return the result in an object native to the programming language.

This is performing two types of function: Extraction of data from an HTML document or fragment, and interpretation and optimisation of that content to match the rules set out by a vocabulary specification.

It is only possible to write a generic parser that covers the first half of this task: Extraction, and application of global rules based on HTML elements and patterns common to all formats.

The purpose of a generic parser (as supported by use cases such as search engines, and other crawlers) is:

To provide a way for tools to extract rich data from a page for native storage, such that the data may be interpreted later by applications. This allows microformats to be crawled, and indexed, and removes the need to include complex HTML parsing within every implementation of microformat data.

Microformats will continue to define various vocabulary-specific optimisations. as part of the design to be optimised for authors. For example: The fn pattern in hCard 1.0, or the lat;long pattern in Geo, as well as default values for properties, such as the maximum rating in an hReview 0.4 (in progress).

  • Actually, no, as it is defined currently, microformats 2 drops vocabulary-specific optimizations. Such optimizations have often been too inapplicable, error prone or i18n-unsafe (e.g. fn to given-name + family-name fails for both numerous cases where middlenames/initials are used, and in general in numerous Asian languages where given/family name order is the reverse of Western English conventions, or languages with multiple family-names, e.g. Spanish - see hCard resolved issues for more). This is a deliberate cutting of a "feature" from microformats 1, it is a deliberate model simplification design decision. Tantek 12:43, 4 October 2011 (UTC)

Microformats 2.0 should refer only to extraction of microformats. Vocabularies should in turn document their appropriate optimisations, which will need to be applied by implementations, or a companion to an extractor, which I'll refer to here as an ‘interpreter’.

  • Vocabularies will no longer have optimizations, this is again deliberately, as they've been shown to be more error prone than helpful. Thus there should be no need for any vocabulary-specific 'interpreters'. However, due to design quirks in various legacy/interchange formats, export conversions algorithms to those legacy/interchange formats will require some additional legacy-format-specific rules (e.g. odd "required" rules in rfc-4287 or vCard specifications will require specific synthesis rules, limitations in said formats will require filtering of some values, e.g. vCard RFC 2426 BDAY disallows vague birthdays like year-month and --month-day - subsequently allowed in vCard 4 RFC 6350). Tantek 12:43, 4 October 2011 (UTC)

A microformats 2.0 ‘extractor’, in combination with the functionality of a domain and format-aware ‘interpreter’ (either another shared component, or part of the implementation itself) would be equivalent to a microformats 1.0 ‘parser.’

  • A microformats 2.0 parser is both generic (no knowledge of specific vocabularies), and lacks any/all such vocabulary-specific rules as compared to a microformats 1.0 parser with the exception of a 1) a limited list of well-established/interoperable backward compat root class names (of current microformats that are or can be soon shown to be specifications/standards per the The microformats process), 2) flat sets of backward compat property names (some with prefix/name specific conversion) for each of those backward compat root class names. This is a deliberate design decision that makes microformats 2 more "micro", and yes this means that even with such backward compat support, this simple form of backward compat may mean that some existing microformats 1 content breaks. We'll assess those and iterate on a documented case-by-case basis rather than attempt to maintain theoretical 100% backward compatibility (since many current microformats format-specific-features are either unused, or may have caused more problems than solutions). Tantek 12:43, 4 October 2011 (UTC)

N.B. I'll rewrite some of these as microformats-2-parsing-faq to help better clarify. The reasoning that led to most of these design decisions is documented in the microformats 2: About This Brainstorm section and following sections. I'll recheck those sections to see if/where reasoning for some of the above noted design decisions may have been missed, and back-fill accordingly. This is necessary because microformats2 is a evolutionary result of simultaneously addressing both numerous generic Microformat Issues as well as various common format-specific problems in microformats 1 syntax and vocabularies. The very number of changes may make it more challenging (from a microformats 1 perspective) to see why any particular design change has been made. Tantek 12:43, 4 October 2011 (UTC)

Parsing Literal Values

It is proposed for microformats 2.0 that all microformats be parseable from just their root element, e.g. <p class="h-card">Ben Ward</p> would create an hCard with the following properties after extraction and interpretation:

   { 
       type: [hcard]
     , properties: {
         'fn': ['Ben Ward']
       , 'given-name': ['Ben']
       , 'family-name': ['Ward']
     }
   }

It is required of the extractor to understand that when a microformats object specifies no explicit child properties, that it must treat h-card as p-fn. But, the parser is generic, so it would also treat h-review, h-entry, h-recipe, h-geo as ‘p-fn’. As a parser, this is somewhat acceptable, but is unacceptable to the vocabularies, many of which do not define fn and that even if all various of fn, summary and entry-title be consolidated to fn (which it is also proposed be renamed to name), it cannot with certainly be claimed that every one of these formats provide anything semantically valid in that case. What, for example, is the ‘name’ of a geo? It has none. Likewise, a review described with just a single field would more likely map to the review's content, not its name, and an Atom entry its content, not its title.

To avoid overloading or undermining the semantics of a vocabulary, I propose that we handle this at the extractor level in a simpler fashion: Define a new property for literal data, that an extractor will provide if no other information was available. All interpreters may then be instructed that in the event that an object has no properties, it can attempt to interpret the literal value from the page instead.

This enables a parser to operate generically without incorrectly applying semantics, and allows applications an interpreters to work with parsed data is a simple and defined way.

In existing microformats, the closest existing example we have for this is the label property in hCard, which is used to represent the literal address label for a place. It is a corresponding piece of fn, org and adr in combination, but has no structure in and of itself.

Possibly, every microformat could have a label form where structured data is unavailable.

Alternatively, value is used throughout microformats to target a generic value (e.g. in combination with price in hListing.) It has been proposed that when parsing properties that are also themselves microformats, we create native objects of the form:

   {
       'value': '1900 12th Street, San Francisco, CA 94'
     , 'type': ['adr']
     , 'properties': {
           'street-address': '1900 12th Street'
         , 'etc': 'etc'
       }
   }

We could apply this same pattern to the root level:

   { 
       type: [hcard]
     , properties: {}
     , value: 'Ben Ward'
   }

In this case, an interpreter or implementation is responsible for using value in place of fn, or restructuring the object. It would be the responsibility of each vocabulary to define its root property. The parsing layer of microformats 2.0 would not impose semantics or naming onto that.

For another example, geo would end up like this:

   {
       type: [geo]
     , properties: {}
     , value: '1.3232;-0.543'
   }

Other Interpretation/Parsing Notes

Collection of other unresolved parsing issues in a generic model:

  • The include pattern references other elements from elsewhere in a document. A generic parser needs to track IDs and fill them in after walking the DOM. (also, itemref if adopted.)
  • Will itemref always map to an item property name?
  • hAtom 0.1 implies author from an hcard in a page that uses an address element. This requires format knowledge, but a generic parser does not currently track the element type of a property node. Should it?
  • hAtom 0.1 defines that the highest level heading within an entry implies entry-title. This particular optimisation might be better off dead.
  • hAtom 0.1 defines that permalinks be parsed from rel attributes, not class
  • XFN - The XHTML Friends Network is entirely built on rel (although, has various other differents from structural microformats, as do vote-links, so perhaps are excluded from this discussion and will always be handled by dedicated parsers/queries regardless?)