Standalone SDO-based variables are similar to ordinary BPEL XML-DOM-based variables. The major difference is that the underlying data form is SDO-based, instead of DOM-based. Therefore, SDO-based variables can use some SDO features such as Java API access, an easier-to-use update API, and the change summary. However, SDO usage is also subject to some restrictions that do not exist with XML-DOM-based variables. The most noticeable restriction is that SDO only supports a small subset of XPath expressions.