OpenMath

OpenMath is a standard for exchange of mathematical objects, currently (2014) at version 2.

In the future, OpenMath3 is expected to be equivalent to strict Content-MathML3; both of these standards are under construction. It is mostly MathML that has been changed to match OpenMath.

Basic OpenMath tags (node types):

OMI

Integer

OMF

Floating-point number (64-bit IEEE, i.e., a double)

OMV

Variable

OMS

Symbol defined in some external Content Dictionary (CD).

OMA

Application (like function application)

Composite OpenMath expressions are usually constructed as an OMA whose first child is the symbol denoting the operation or function, e.g.

<OMA>
    <OMS cd="arith1" name="plus"/>
    <OMI> 2 </OMI>
    <OMF dec="3.4e5"/>
    <OMV name="y"/>
</OMA>

which is analogous to expr {2+3.4e5+$y}. If parsed by a little XML parser (or tdom), this (modulo whitespace) comes out as

OMA {} {{OMS {cd arith1 name plus} {}} {OMI {} {{#text 2}}} {OMF {dec 3.4e5} {}} {OMV {name y} {}}}

which is not too onerous to process in Tcl.

There are also some more advanced tags:

OMSTR, OMB

Strings and bytearrays

OMBIND, OMBVAR

Used when binding variables (like x is bound by the integral in ∫₁³ x² dx).

OMATTR, OMATP

Used for putting attributions on subexpressions.

OME

Errors

OMFOREIGN

Foreign format data

OMR

References (for sharing subexpressions, much like Tcl_Objs can be shared)