Include data that may be objectively generated some day?

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

Is it good or bad to include, in an XML document, data that is currently not objectively generated but may be in the future?

Please allow me to explain.

Example: Below is information about a book. Suppose that today's applications effectively process its markup and data:

<Book>
      <Title>_________</Title>
      <Author>_________</Author>
      <Date>_________</Date>
      <ISBN>_________</ISBN>
      <Publisher>_________</Publisher>
</Book>

Now, consider the problem of determining how "enlightening" a book is. Assume that there are no objective rules for determining the enlightenment-capability of a book. Manual determination of the enlightenment-capability of a book is subjective and yields mixed results. Thus, automating the determination of the enlightenment-capability of a book is problematic.

Nonetheless, the developers of the Book XML vocabulary decide that someday it may be possible to objectively measure the enlightenment-capability of a book and applications will make decisions based on enlightenment-capability data. So they decide (today) to require that each book contain an <Enlightenment-Capability> element:

<Book>
      <Enlightenment-Capability>__________</Enlightenment-Capability>
      <Title>_________</Title>
      <Author>_________</Author>
      <Date>_________</Date>
      <ISBN>_________</ISBN>
      <Publisher>_________</Publisher>
</Book>

Since the XML documents contain enlightenment-capability data application developers figure "Hey, let's use it."  So, suppose applications (today) start making decisions based on the data in the  <Enlightenment-Capability> element. What will be the consequence?

More generally, what will be the consequence of adding this element to the Book XML vocabulary?

/Roger