Add components section to improve reusability through referencing within the spec

[frankkilcommins]

It's currently possible to compose a workflows document and reference other workflow documents, but referencing capabilities of steps and/or reusing step inputs across workflows or steps is limited.

The current scope and referencing of inputs and outputs for steps and workflows is described by the following picture:

Defining workflow inputs, steps and/or step inputs under a global components section (similar to OpenAPI) could bring better reusability through referencing.

Proposal for Components within the Workflows Specification

Components

Holds a set of reusable objects for different aspects of the Workflows Specification. All objects defined within the components object will have no effect on the workflow unless they are explicitly referenced from properties outside the components object.

Field Name	Type	Description
inputs	Map[string, Schema Object]	An object to hold reusable JSON Schema objects to be referenced from workflow inputs. Remark: possibly trimmed down version of OAS Schema Object
steps	Map[string, Step Object]	An object to hold a reusable Step Objects.
parameters	Map[string, Parameter Object]	An object to hold reusable Parameter Objects

[frankkilcommins]

Would recommend to leverage the concept of reference objects

[MikeRalphson]

possibly trimmed down version of OAS Schema Object

@frankkilcommins what would be the rationale for a cut-down schema object? We have got ourselves into a right state in OAS with subset-superset-sidesets before.

[shaisachs]

I added reference objects just now. Incorporating them into Steps and Parameters was no problem. However, because the workflowInputs is defined to be a JSON Schema object, it's a little more difficult - we need to embed reference objects inside that JSON Schema. Can we modify workflowInputs to something like an array of JSON Schema or reference object? Something like [JSON Schema | Reference Object].

[MikeRalphson]

@shaisachs doesnt the schema object allow $refs anyway?

[shaisachs]

I think so... But I guess we need to mention that in the spec and provide some examples.

[frankkilcommins]

possibly trimmed down version of OAS Schema Object

@frankkilcommins what would be the rationale for a cut-down schema object? We have got ourselves into a right state in OAS with subset-superset-sidesets before.

@MikeRalphson my intention was purely in relation to the explanation text. Optimally we'd just support full JSON Schema 2020-12 here.