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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Designing XML to Support Information Evolution
 > On May 19, 2004, at 10:37 AM, Dare Obasanjo wrote: > > > Hierarchical databases failed for a reason. > > Just to be pedantic, the hierarchical model failed, hierarchical > databases are still chugging along. IMS (a hierarchical DBMS that is > the meanest, nastiest, ugliest mainframe dinosaur) still quietly > manages an awfully big chunk of the world's data: "More than > ninety-percent of the Fortune 1000 companies use IMS. IMS serves 200 > million end users, managing over 15 billion Gigabytes of production > data and processing over 50 billion transactions every day." > http://www-306.ibm.com/software/data/ims/highlights/experform.html > . . . if it ain't broke, don't fix it . . . I used hierarchical databases in the 80's and even into the 90's, but had nowhere the capabilites I do with XML. I think this was primarily due to the fact that a schema had to be defined apriori, and once a schema was set and data loaded, to make changes you had to unload the data (all of it, not just few affected tables), alter the schema and reload. For large systems (like the telecom billing systems I was building with 20-100M new records added everyday), making a schema change became a 2-3 day downtime event to unload/reload data (we now live in a real time world). All the relational model did was break up this single monolithic chunk of data into separately managed tables, so now part of the databse could be down instead of the whole thing... but the structures are still pre-defined, making them less than ideal for eXtreme Programming developments. XML is a true Information Domain. Both the schema (e.g. meta data, tags, elements attributes) and the data are dynamic (I am NOT talking about XSD schemas). One to one relationships are extended to one to many realtionships by simply inserting another instance of the tag into an XML document vs. a hierachical or relational model which requires redesign, with a new part-of or intersection table, with nothing but foreign key relationships. Business requirements change, and with that change come changes to the Information Model. XML is the only representation I have used that is flexible enough to extend itself without a need for a database redesign, which in turn generally means database downtime to make the changes and convert existing data structures. Of course, that is only if you are using a native XML database, and not building XML-Relational mapping layers into an RDBMS, which removes all the flexibility just stated. ------------------------------------------------------------ Owen Walcher xpriori@o... http://www.xpriori.com/ - XML Persistence for eXtreme Programmers 
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