You can use a map to create a structure definition from any input. For example, suppose you have a positional structure that is described by a spreadsheet. The spreadsheet contains a list of element names, sizes, start columns, and further description. You can export this spreadsheet as a CSV file and create a map that maps the contents of the spreadsheet to the Importer structure.
The Importer structure is a predefined structure in the Builtin project (Builtin/Structures/Executable Structures/Importer). When it is executed in a map, the Importer structure can create one or more structures whose elements are defined by the mappings. To use it, create a standard map, and specify the Importer structure as the output structure. You can specify any input structure you like and map the elements to produce the desired elements in the structure. You can build and test your map in the studio as usual, producing the output of the map in XML for testing purposes. The Test Run menu will provide an additional option called Test Run to Importer Structure, which will actually create the structures. You can re-run the map as many times as you like, which creates the structures each time and replaces their contents.