This schema describes a REFERENCE element intended for use in family tree documents. It was developed as an example for Chapter 25 of the XML Bible, 3rd Edition, by Elliotte Rusty Harold (elharo@metalab.unc.edu) Published by Wiley 2004. ISBN 0-7645-4986-3. This schema is placed in the public domain. Please feel free to use it or adapt it in any way you like. The SourceType is used exclusively for REFERENCE elements. Each such element has a unique ID attribute by which it can be referred to, and PCDATA content identifying the source of the information; e.g., a document, an interview, personal recollection, etc.