Schema Design

Schema design is a very broad and complex topic. As much as I would like to offer you my knowledge and opinions about it, I'm afraid it would qualify for another complete chapter, if not another book. I have to set an appropriate scope somewhere for a book that has already turned out longer than planned, so I'm going to point you elsewhere for details about schema design. There are several good resources listed at the end of the chapter. Beyond that I'll offer only a few general observations.

Despite what some authorities may tell you, no single technique is right for all circumstances. If you're going to design only one or a few schemas, probably any approach that provides the required validation will be adequate. This includes letting an IDE like XMLSPY or TurboXML generate a schema from a representative instance document as I discussed in Chapter 6. On the other end of the spectrum, if you are designing several documents for a fairly large system, you would be well served to take a more disciplined approach. I favor creating type library schemas containing simple and complex types that are reused in other schemas, similar to the approach discussed in Chapter 4 that was considered by X12 and OASIS. However, there are certainly other techniques.