accepted-limitations-of-microformats

Introduction

This document attempts to outline certain accepted limitations of Microformats. These limitations are partly why Microformats are so simple and easy to implement. Simplicity, however, comes with trade-offs and thus you should be aware of the types of problems that Microformats are not intended to solve.

Microformat Scoping Issue

A good real-world example of the Microformats Scoping issue is outlined in the following section. Let's take the following text and try to mark it up using the hCard Microformat:

Janet Seymour and Robert Tripton are available via phone.
Rob is available at his home number: 555-555-5555.
Janet can be reached at her work number: 777-777-7777.

A publisher would want to mark-up Janet and Robert's telephone contact information. Not knowing that Microformats are scope-less, they might take the following approach:

<div class="vcard">
  <span class="fn">Janet Seymour</span> and
  <div class="vcard">
    <span class="fn">Robert Tripton</span> are available via phone.
    Rob is available at his home number: <span class="tel">555-555-5555</span>.
  </div>
  Janet can be reached at her work number: <span class="tel">777-777-7777</span>.
</div>

Unfortunately, the Microformat parser would generate the following two Microformat outputs:

hCard
  fn  -> Janet Seymour
  tel -> 555-555-5555
  tel -> 777-777-7777

hCard
  fn  -> Robert Tripton
  tel -> 555-555-5555

The reason this would happen is because both hCards overlap. Microformats do not have an established mechanism for identifying which properties go with which VCARD. When it parses Janet Seymour, the first telephone number it finds is Robert Tripton's, not Janet Seymour's. Since the parser doesn't know which person 555-555-5555 belongs to, it mistakenly adds it to Janet Seymour's list of phone numbers. This problem happens whenever you have more than one Microformat of the same type that overlap one another.

Keep in mind that the Microformat authors are aware of this limitation, and that the limitation is fine for what the Microformats community is attempting to accomplish - provide a simple mechanism for semantic data markup. Simplicity has its benefits and its drawbacks. RDFa allows you to specify which property goes with which VCARD and solves this issue, at the added cost of a small amount of extra syntax.

Microformat Namespacing Issue

(This should be changed to a REAL issue NOT a theortical one. By simply changing hAudio's TITLE to FN, solves all issues in this example. PLEASE replace, it is miss-leading and un-true in this case, this is why we select good property names from the begining to avoid these issues. If there is a real issue please document it, otherwise there is no need to continue to spread FUD)

The following is a theoretical example, based on work performed for hAudio, that shows how not having namespaces can be detrimental to scalability. There was a discussion on the New Microformats mailing list regarding the re-use of the 'title' property from hCard. Re-use of property names in Microformats is heavily encouraged, but it creates several problems:

1. If somebody narrowly defines the meaning of a property, re-using that property is difficult if not impossible.
2. The more you re-use a property, the more risk there is of property name clashes when Microformats overlap on a web page.

The question of whether or not we should be using title when referring to the title of a song, or the title of an album, was raised several times while discussing hAudio. The definition for the word 'title' in this sense is:

5 a) the distinguishing name of a written, printed, or filmed production 
  b) a similar distinguishing name of a musical composition or a work of art.

Unfortunately, the hCard authors narrowly defined title. They re-used the VCARD definition. The VCARD specification defines title as:

To specify the job title, functional position or function of the object the vCard represents".

This means that any Microformat that desires to use title must use the definition used by VCARD, since that specification was created first and changing it might confuse people who have adopted VCARD. Having a namespace would fix this problem as "hCard:title" could mean something subtly different from "hAudio:title" - however, since there are no namespaces in Microformats, this distinction cannot be made.

Let us assume for a moment that "title" was defined in such a way that would have allowed hAudio to re-use the property. There is another problem that goes back to the example given in Appendix A. How do you differentiate between two Microformats that overlap with the same property name? Take this sentence for example:

Freddie Mercury, known for a song called Bohemian Rhapsody, was the lead singer for Queen.

The HTML markup would look like this:

<div class="vcard">
  <span class="fn">Freddie Mercury</span>, 
  known for a song called
  <div class="haudio">
    <span class="title">Bohemian Rhapsody</span>,
  </div>
  was the <span class="title">lead singer</span>
  for <span class="org">Queen</span>.
</div>

The Microformat parser above would generate the following two outputs:

hCard
  fn    -> Freddie Mercury
  title -> Bohemian Rhapsody
  org   -> Queen

hAudio
  title -> Bohemian Rhapsody

Even though title is the desired word to use, due to the scoping issue explained in the previous section, and because Microformats do not have namespaces, we were forced to use a different property name. hAudio currently uses the property name audio-title and album-title in an effort to avoid namespace and scoping issues. Ironically, the use of the dash character in "audio-title" and "album-title" is a very simple form of namespacing... something that Microformats were attempting to avoid.

This limitation is also well known to the Microformats authors and is currently viewed as an acceptable price to pay for an easy-to-implement markup mechanism for publishers. RDFa has namespacing and thus solves this issue, at the added cost of a small amount of extra syntax.