more typesafe

[kvlahromei]

Swagger offers ways to formalize the input/output:

• https://github.com/swagger-api/swagger-spec/blob/master/versions/2.0.md#dataTypeFormat
• https://github.com/swagger-api/swagger-spec/blob/master/versions/2.0.md#schemaObject

This includes esp. following sections

• service.type
• attribute.datatype
• request.requested_datetime
• ...