model meta data

[abramvandergeest]

@mellistibco and I have discussed what we should have in the model metadata flag of the specification. I have suggested that the model flag should contain a json object that can have whatever flags the user wants to describe how the preperation structure is going to be used. Matt has suggested that we create a rigid complex structure that can be used by code outside the implementation to set up the pipeline of features/model.

[abramvandergeest]

We have decided that generally a rigid specification for the model metadata would be very useful in deploying any implementation of the specification, but that it isn't an immediate priority. So for now we will leave the simple structure (very TensorFlow based) that currently exists, but with the intent of soidifying the model metadata structure in the future. Until that time this issue will be left open.