4.2. Descriptors

Descriptors allow users to define a controlled vocabulary with which to describe the physical context of an AI task. Each descriptor defines a term in that vocabulary, which is comprised of a name, a datatype, and bounds on that data type. If you are familiar with the GEMD data model, descriptors are roughly equivalent to AttributeTemplates.

The AI Engine currently supports 5 kinds of descriptors:

Real Descriptors
Integer Descriptor
Categorical Descriptor
Chemical Formula Descriptor
Molecular Structure Descriptor
Formulation Descriptor

4.2.1. Real Descriptor

RealDescriptor is used to represent continuous variables. Each Real Descriptor must provide a lower and upper bound, which is used to both validate input data and as a prior when making predictions. If you are not sure what bounds to use, you may want to look at the attribute templates to see if another user has defined bounds for you. It is better to err on the side of broader bounds than narrower ones.

Additionally, each Real Descriptor defines the units of every variable associated with that descriptor. Any GEMD-compatible unit string may be used. If a variable is dimensionless, you can use an empty string.

4.2.2. Integer Descriptor

IntegerDescriptor is used to represent discrete, dimensionless variables. Each Integer Descriptor must provide a lower and upper bound, which is used to both validate input data and as a prior when making predictions. If you are not sure what bounds to use, you may want to look at the attribute templates to see if another user has defined bounds for you. It is better to err on the side of broader bounds than narrower ones.

Integer Descriptors are dimensionless and units cannot be specified.

4.2.3. Categorical Descriptor

CategoricalDescriptor is used to represent variables that can take one of a set of values, i.e., categories. All of the possible categories must be known ahead of time and specified in the Categorical Descriptor.

4.2.4. Chemical Formula Descriptor

ChemicalFormulaDescriptor is used to represent variables that should be interpreted as chemical formulas. The Chemical Formula Descriptor has no parameters other than a name.

4.2.5. Molecular Structure Descriptor

MolecularStructureDescriptor is used to represent variables that should be interpreted as molecular structures. Both SMILES and InChI are supported. The Molecular Structure Descriptor has no parameters other than a name.

4.2.6. Formulation Descriptor

FormulationDescriptor is used to represent variables that contain information about mixtures of other materials. The Formulation Descriptor has no parameters other than a name, of which the two allowed values are ‘Formulation’ and ‘Flat Formulation’. The key ‘Formulation’ should be used when referring to mixtures found directly in the training data, for which the ingredients may be other mixtures themselves. The key ‘Flat Formulation’ should be reserved for mixtures comprised of only raw ingredients produced by a SimpleMixturePredictor.

The two allowed formulation descriptors can be obtained by the helper methods FormulationDescriptor.hierarchical() and FormulationDescriptor.flat() that produce descriptors with the keys ‘Formulation’ and ‘Flat Formulation’, respectively.