All file operations, including reading a file based datasource (XML, JSON, OData, etc.) use a Windward access provider. Access providers exist for all the common protocols (file servers, basic, digest, OAuth2, etc.). And if you need something different, you can write your own access provider - once. And it then handles any access of files using that protocol. (ref: Ohana)
If set, when a report is generated, all data placed in the generated report is also written to a data.xml file. That file is then included in the generated DOCX, PPTX, or XLSX report.
When generating a report, lists of values or select criteria can be passed to the engine to have it apply that ad-hoc query in the select for the identified tag.
When Windward is merging the data into a template, it process the template handling each tag in order, and the tags can pull from different datasources. This allows the select in a tag to use data from other datasources in the select.