Eric Inman (7/4/2009)
Mike C (7/4/2009)
If you're interested in guaranteeing data stored in the database is valid you have to use the database engine to check it, just like any other database-side constraints. You can always check data in client apps or in the middle tier before it gets stored in the database, but there's no guarantee that these methods of enforcing constraints on data can't be circumvented (by a DBA with direct table access, for instance).Understand, but I just dont think that passing around a string with over 95% waste in every packet gets that done. I enforce the data requirements in my domain, not the data interface. Over the last few years I have noticed that people are moving more to enforcing the domain data in the data interface layer and not in the domain iteslef. I dont know how this can hold up when said data becomes more than a trivial xml hierarchy.
Ahhh, the old "wasted packets" argument. Fortunately for all of us there are many methods of optimizing network traffic through various compression algorithms, in any of several network protocol layers. The 95% waste you're referring to is highly compressible, as XML itself tends to be highly compressible. The trade-off for the waste is proprietary technologies that are difficult to work with, require a lot of binary data manipulation and custom programming and don't play well with firewalls. After all, DCOM is relatively efficient over the wire, but the tradeoff for that savings in network bandwidth is proprietary technology + higher admin and maintenance costs.
XML Schema, which the author writes about in this article, makes it fairly easy to enforce domain level constraints on individual elements and attributes of your XML data. Of course you can always shred your XML in the business logic layer and store it as purely relational data (which is what I normally recommend, except in the case of exceptional circumstances or hard requirements to the contrary).
XML Schema supports fairly complex data constraints, including regular expressions for strings, ranges and sets for numeric values, etc. Jacob Sebastian has written a free e-book ("The Art of XSD") that describes it in detail. I don't have a link handy, but it's distributed by Red Gate -- definitely worth Googling if you want to see what types of constraints you can define with it.