The Predictive Model Markup Language (PMML) is a mark up language for statistical and data mining models. Some sort of HTML language to handle statisical tasks such as regression, decision trees etc.
PMML is an XML-based language which provides a way for applications to define statistical and data mining models and to share models between PMML compliant applications.
PMML provides applications a vendor-independent method of defining models so that proprietary issues and incompatibilities are no longer a barrier to the exchange of models between applications. It allows users to develop models within one vendor's application, and use other vendors' applications to visualize, analyze, evaluate or otherwise use the models. Previously, this was very difficult, but with PMML, the exchange of models between compliant applications is now straightforward.
Since PMML is an XML based standard, the specification comes in the form of an XML Schema.