A few notes:

- EMF is used as an implementation  mechanism in some of SDO implementations, such as Tuscany. EclipseLink SDO for example doesn't use it at all.
- Probably you're using some old jars. You'll see SDO in Websphere too, but it's the old SDO classes, and latest Websphere doesn't support the SDO standard.
- don't look at EMF to find the answers. It's got nothing to do with your problem. Read more on SDO and DAS, how payloads are specifically defined with XSD and how datagrpahs and dataobjects sit on top of it.
- SDO and SCA are closer to architectural concepts than technologies. You just can't include an sdo jar in your app and have it fly! You've got to design your application  that way. So you've got a lot to do if you want to go this way!