Need for a Tonal Centre or Tonic object

[SteveALee]

I'm wondering if a missing piece of semantics is the tonic (or more broadly tonal center)?

I've been thinking about relative pitch - eg Solfege and Nashville numbering and how they fit in with notation and tools. I started wondering if MNX needs to support them explicitly but after exploring with a small app I decided relative pitch can be derived from absolute semantics, with possibly a single missing part.

Relative doh Solfege and Nasville numbering are important and useful schemes, especially for ear training or ear based music learning and sharing. However, it seems not often supported by apps etc, perhaps due to a general fixation on absolute notation (score), at least for Western music.

The following is my understanding and rough analysis - but I'm relatively new to music and harmonic concepts so I may well be way off.

In tonal music given a Key an absolute pitched note can be easily converted to relative Solfege Do or Nasville 1 based on a notes distance in the key scale from the Tonic. This works for harmony or chords (when considering the root).
 
Given a major scale there are actually 7 possible tonal centres (modes) but the Tonic identifies which is in use. eg for C major scale A minor is the relative minor with a tonic of A. Relatively A is La, 6 or Aeolian . For melody there seem to be two common approaches: either change the tonic Do(1) to A or else use La(6) based notation. For harmony the Tonic chord always seems to be changed to A-

But in musical scores and current MNX the is no concept of a Tonic - just the key signature. These leaves undefined which of the 7 possible tonal centres is intended. It's up to the reader to infer the missing semantics. And thus software also needs to infer Do or 1 for relative pitch systems (and the tonal centre if it is not Do - eg La based minor)

So would MNX benefit from an optional "tonal centre" object with a value from 1 to 7? I don't think the use of Do or La based minor needs to be in the semantics though as it's an interpretation. What matters is the tonal centre is the 6th degree of the major scale defined by the key signature,

Given the aspirations for MNX given in https://w3c.github.io/mnx/docs/ it seem to me that this might be worth considering.

[SteveALee]

As a practical example of how tools and interchange do not support relative I recently exported a chord chart from IReal Pro in musicXML to MuseScore. I wanted to change the Chords to relative Roman Numerals. But as MuseScore has no sematics for Chord names they are just text labels and I had to edit them all rather than just select "Roman Chords" say.

In the case of a Chord Chart requiring the MNX document to specify Key Signature and Tonal Centre might seem extra effort but it would make the semantics explicit and avoid requiring tools or user to infer.