Use a Standard or Roll Your Own?

There are always benefits to not reinventing the wheel, and this rule holds true when considering schemas for common business documents. However, though a sad prospect to consider, the wheel you're looking for may not have been invented yet. This is one area where I will offer some somewhat unqualified guidance. If you can find a schema that fits your purposes and has acceptance in your community as a standard, then by all means use it. If you can't find one that fits or if you find more than one and there is no consensus in your trading community or user base about which one is “standard,” then you have at least a few different ways you can go. If one or more schemas might work but aren't universally accepted, there are a few criteria you could use to select among them. One criterion might be the number and quality of other programs, stylesheets, sample documents, and documentation available for the schemas. Another might be whether or not you can use the schemas on a royalty-free basis. If you do find an existing schema that is attractive from a number of these perspectives yet doesn't fully accommodate your data, it may still be a good fit for you if you can easily customize or extend it. However, if all else fails, don't have any hesitancy about developing your own schema.

Choosing or creating an XML format is an important decision, but your particular choice is probably not going to be extremely critical. If people don't like the formats you have selected, they can always perform transformations (particularly if you make it easy for them, as we'll discuss later in the chapter). Go back and review the first part of Chapter 10 on XSLT if you like; transformations are something we are going to live with for several years to come, if not forever. The rest of this section deals with general issues regarding designing your formats.