Build Rich Complexity from a Small Set of Well-Defined MarkupCombinators

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

Hi Folks,

Consider the digits 0 - 9. They can be combined to create an infinite number of integral numbers, such as 256 or 14 or 190023156001200021345. Each digit has a well-defined meaning and the rules for combining the digits are well-defined.

Rich complexity flows from a small set of digit combinators.

Next, consider XML Schema. It is a markup language consisting of a small set of well-defined markup combinators:

    1.  Schema
    2.  Element
    3.  Attribute
    4.  Simple Type
    5.  Complex Type
    6.  Attribute Group
    7.  Element Group

The language has well-defined mechanisms for combining the markup combinators:

    1.  Schemas are combined using import, include, and redefine
    2.  Elements are combined using sequence, choice, or all
    3.  Complex types with simple content are extended or restricted
    4.  Complex types with complex content are extended or restricted

An infinite variety of schemas can be created using the 7 markup combinators and the 4 combining mechanisms.

Interestingly, XML Schemas is considered to be a complicated language. Perhaps 7 markup combinators are too many in a markup language?

When creating an XML markup language consider following this approach:

    1.  Create a small set of well-defined markup combinators. From experience with XML Schemas, 7 or less markup combinators might be adequate.
    2.  Create well-defined mechanisms for combining the markup combinators. Again, from experience with XML Schemas, 4 or less combining mechanisms might be adequate.

From that will flow complexity of great richness.

Comments?

/Roger