# MDDL: The Math Data Description Language and MathHub data hosting.

The MDDL allows mathematical data set creators to describe the meaning of mathematical objects in a data set and their database encoding declaratively and then generate data tables, user interfaces, and update facilities from them. MDDL uses

**object theories**that specify the mathematical types of objects**data base theories**that specify database types,**codecs**(encoders/decode pairs) that mediate between them, and finally**schema theories**that bind all of them together, and provide metadata-based hints for infrastruture generation.

All of these are regular flexiformal theories, that can make use of the existing MathHub libraries. Consequently, a mathematical data colletions are regular MathHub Library with MDDL schema theories.

**MDDL archives**for the schema theories. The main one is usually just called`mddl`

.**VT archives**for the virtual theories generated from the`mddl`

archive, the main one is usually called`vt`

An example of a MDDL-based schema collection can be seen in MathHub (MDDL, VT, and the generated data collection *Symmetric Objects*)