Re: Are we losing out because of grammars?
From: Ken North <ken_north@c...> > Using application code to enforce rules, instead of declaring constraints > that are managed by the container (database), leads to versioning problems. > In the XML world, we can now exploit types and constraints, but one question > is whether developers will learn from the SQL experience, i.e., declarative, > container-managed logic solves some of the proliferation/fragmentation > problems that occur with ad hoc application logic. When you say "container (database)" I am not sure if you mean big documents with full markup or centralized DBMSs. If the latter, then I wonder whether, to some extent, people like XML because it holds the hope of escaping from centralized DBMSs; in other words, the important SQL experience has to be judged with different architectures in mind, in particular for data delivery not just data querying. For example, what is the schema for routable documents which get information added as they pass through different stages (i.e. orders, etc.): is it just the union of any data that is added at any time? Underlying Murata-san's RELAX seems to be that we should start from desirable properties that web documents need: lightweightedness, functioning even if the schema goes offline (hence no PSVI) and modularity. I think underneath James Clark's TREX is that we can support plurality if we have a powerful-enough low-level schema language into which others can be well translated. I think underlying W3C XML Schemas is that a certain level of features and monolithicity is appropriate (though perhaps regrettable) because of the need to support a comprehensive set of tasks and to make sure that there are no subset processors (validity should always mean validity); however the processors are monolithic but the schemas are fragmented by namespace. Underlying Schematron is that we need to model the strong (cohesive) directed relationships in a dataset and ignore the weak ones, that constraints vary through a document's life cycle, and that lists of natural language propositions can be clearer than grammars. So there should be a class of standard constraint languages which are not platform-API-dependent (e.g., not .NET code, not Java code, not Python) but lightweight-enough to get widely deployed and which cater to stakeholder group's particular requirements, as well as schemas for DBMSs. A trouble with the centralized view seems to me that it always will focus attention on issues of "efficient storage and query" which are somewhat (sometimes utterly?) extraneous to the needs of data on-the-wire. Cheers Rick Jelliffe
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