[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Caution using XML Schema backward- or forward-compatibilit
Stephen, Actually yes. Its a mess, isn't it? If we have to do a non-zero amount of validation in application code, how much value do we get from a loose schema? Is doing validation in two places really good design? Schema validation gets turned off usually because it is costly in CPU cycles but all too often that exposes the application to a range of failure modes that are discovered empirically. For a significant system I'd quite frankly rather spend the money on something like a DataPower box or two to do Schema validation and Schematron with hardware assists than try to deal with an exciting range of outages (or worse, subtle data corruption) caused by hand-checked or unchecked data inputs to a system that we accept because we want to hold down the number of CPUs and application server licenses. The effect of the all-too-common approach of validating in multiple places that you describe is to make the pain caused by a change larger and more difficult to assess with any accuracy. In change management terms application software-based validation makes the problem worse. Far worse if you don't control both sides of the data exchange. Is there any such thing as a generally compatible schema change? Sure we can define extension points or whatever in the schema, make elements optional, but considered holistically how much benefit do we really get outside of avoiding changes to the schema itself? I'd like to see some discussion of the schema change/code change trade-off in both open and closed environments. Greg On 12/27/07, Stephen Green <stephengreenubl@g...> wrote: But you accept that making things mandatory in the schema will
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