PortfolioLoaderTool?

Hi,

When I load porfolio data using the PortfolioLoaderTool, it has a parameter -t,–structure A /-separated sequence of position attributes used to structure the portfolio(s) (e.g.trade-group/strategy), I don’t understand that meaning, Would you please give me a specific example to use this parameter? The following is reference,
https://opengamma-docs.atlassian.net/wiki/display/DOC210/Loader+tool

In addition, Is position attributes be stored in pos_attribute table? what values is ATTR_KEY and ATTR_VALUE field in pos_attribute table? Would you please give me an example?

Thanks!