Re: What does this NULL mean?

Alfredo Novoa schrieb:

>>>Database design maintenance has nothing in special.

>>Well then neither does the original database design.
>>One is just as critical as the other.

Catalog and (user defined) database belong to different layers. They have so big differences that cannot be viewed as one data model. Just for example:
- what is row in catalog can be a dimension (column) or a table in user level model.

For example, delete a row from a table in your database catalog. What happens then? Probably, a column or a table will be deleted. But it is not described anywhere in your model because there is no such a model that could handle such dependencies. This behaviour is hard-coded into every database system rather than is part of its data model.

Currently there are no appropriate tools for modeling catalogs and other types of meta information.

> You are trying to mud a very simple issue for unknown purposes.

That is not a simple issue. It is one of the most complex open problems. For example, what if I need to create a catalog of catalogs?

>>In that case, out with the trivialised summary of
>>schema evolution.  You have the floor.  Please outline
>>what Date has said about this issue.

That would be the same as applying, say OOP, to the problem of manipulating data in general and schema in particular.

> A very elegant and powerful way. Isn't it?

Using your approach we can apply even more powerful way: manipulating directly molecules and atom of the CPU where our data is being processed. Indeed, why not? And then, according to you, we do not need more complex and sophisticated technologies. All atoms are equal, no hierarchies, no complex dependencies, no constraints. Just move atoms back and forth and produce right order that corresponds to the new state of data.

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