Don’t create elements with simple content and attributes

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

Hi Folks,

I hold this to be the fundamental axiom of XML:

          Make the structure of data explicit.

We accomplish that by adding a label (markup) to the data.

There are various terms for this notion of making the structure of data explicit: upconversion and uptranslation.

Elements with simple content and attributes are antithetical to the fundamental axiom of XML.

Here is an element with simple content and an attribute:

<Cost currency="USD">8.95</Cost>

 

The data USD is explicitly labeled. The label indicates that USD is a currency.

What about the data 8.95, is it labeled? No! It is anonymous/unlabeled. Note: Cost is not the label for 8.95; Cost is the label for the whole package.

In my most recent post, I asked, “What is that number (8.95)?” I received excellent responses: 8.95 is a price, 8.95 is an amount, etc. External knowledge was needed to label the data. The need for external knowledge completely contradicts the fundamental axiom of XML.

Therefore, don’t create XML like this:

<Cost currency="USD">8.95</Cost>

instead, create XML like this:

<Cost>
    <Currency>USD</Currency>
    <Amount>8.95</Amount>
</Cost>

 

Do you agree?

 

/Roger