Does the url field in the TES output require a scheme?

[claymcleod]

All of the examples in the specification require a scheme to be present (gs://, s3://, file://), but the specification does not explicitly state that a scheme is required. I had an example today of a TES server that wanted a path with no scheme to upload to object storage. So my questions are,

• Are schemes required to be present in the url field, and
• Is there a defined list of supported schemes or is that implementation specific?

Learning from WDL, it might be beneficial to require that at least a handful of schemes are supported for cross-platform compatibility.