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Hi Jonathan: I am forwarding this to the Human Markup list. Sean is on that and understands the context of current discussions there. I am curious about various approaches that tie it all together and in this particular case, wondering if for some time period it may be wise to focus on the instances and therefore, XML Schemas as a simple means to get definitions for instances. In total there would be many modules, but to begin with, having chosen some categories of information, we sort out membership of various documents and record that sorting in the document type (schema). It takes a "feel" for the data domains followed by normalization, then iterate until it *feels right*. Is that too... Extreme? I understand that you are looking at a type system independent of the schema language. I need to understand that better. My dilemma is "too many moving parts", that is, having so many ways to design that it becomes difficult to choose. Schemas I know so I tend toward what I know and that isn't always the best metric. I like your approach in that it appeals to my need to start as much as possible from simple devices. If we have the instances nailed down, we have a pretty good idea how to then begin to look at different schemata techniques and thus, which one best models some particular kinds of constraints because we know what the outputs look like. If we got the categories right, we are in the right neighborhood. So I am following this with great interest. I realize how unscientific it all sounds, but after some years of doing this, I am convinced schema design is art supported by method. :-) Len http://www.mp3.com/LenBullard Ekam sat.h, Vipraah bahudhaa vadanti. Daamyata. Datta. Dayadhvam.h -----Original Message----- From: Jonathan Borden [mailto:jborden@m...] I am discussing a type system that is independent of schema languages. > Then in a data-centric design, I would concentrate on one > schema language, and more particularly, I would > concentrate on the instances I wish to produce. Sure, but the question is in the context of "how do I make sense of these different systems"? > > Yes? Or what does it mean to say "instances are equal"? An "Instance set" is the set of all possible documents which are valid with respect to a particular schema, for example a specific DTD. This says that two DTDs dtd-a and dtd-b are "equal" if the set of all possible documents that are valid with respect to dtd-a is equal to the set of all possible documents that are valid with respect to dtd-b. (note that i don't provide a mechanism for actually computing this set, i don't have too as this is a formal definition). > > In a relational system, it is as if one designed > the report data, then designed the tables, then designed > the queries that produce the reports. Then they > discover the business rules. Then they create the > GUI. Excellent analogy! In SQL, you don't tell the system _how_ to compute the data, rather you tell the system _what set_ of data you want, and the implementation (e.g. query engine) does the work. > > Naive yes, but I want an explanation I could give > to a naive person. If I have to resort to explaining > QNames, the explanation is DOA. > Well then don't try to explain XML Schema datatypes, as they are defined by QNames :-) Think of a schema as a box with a light on top and a door on the side. The Instance Set of a Schema is the collection of all the documents for which the light turns on when you stick the document inside the door of the box. Now suppose you have 4 of these boxes, all painted black. You are told that there are two types of Schema boxes, and you are assigned the task of sorting the schema boxes into two groups. As you stick each of your documents into the boxes you find that for two of the boxes, half the documents cause the box to light up and for the other two boxes the other half of the documents cause the box to light up. You now have your two groups of documents, and two groups of schemata. We say each of the schema in the group is "equal" because they each have the same set of instance documents. -Jonathan
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