MEETING 3/12/97 CLASSIFICATION 
Attendees: Serge, Jason, Roy, Vasilis, Yue, Janet, Michael.

very lively discussion with a lot of misunderstanding.

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CLASS: set of objects with the same structure
	in Lorel: structure may be not exclusive
	e.g., name and address and perhaps more

Class/type: All objects with that structure
Class/extent: A set of objects with that structure

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SPECIFICATION OF A CLASS: alternatives

1.	all objects with a certain pattern (e.g., with a name and address)
2.	all objects satisfying a certain (complex) predicates
3.	all objects returned by a query
4.	by extend (Michael -> explict insert/delete + constraint checking)

All objects in a class have the same structure  
	
The "type" is either explicit (3. - the pattern), derived 
(2. and 3.), enforced by the system (4. - constraint)

Yue's question: what is the difference between a view and a class?

Answer is unclear: a class is a view by intent in 1./2. 
(by extent in 3.) that returns a set of objects? 
[4. is not a view but stored info]

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WHERE IS THE CLASSIFICATION:

1. in the database -- this is re-introducing types in OEM
Serge's heretic belief: one cannot live only with OEM but 
in an ODMG+OEM world. 
*** like workspace this is an extension to OEM/LOREL
	
2. only in a view -- do not change the OEM world.

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WHAT IS IT GOOD FOR:

1. view specification: I can decide to view all PERSON objects
differently in a view, e.g., hide their salary.
	
classification becomes mixed with other view specification 
features (Jason)

2. application programming: a programming language such as C++ expects 
some types.  The current API ignores types so is hard to use (Roy).

3. interface: it is easier to say that I want people who make more 
that 10K.   Difference with a view?

4. query processing: I define the class PERSON and I want an index on
all PERSON.  Or I store differently all objects in class PERSON.

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ORTHOGONAL ISSUES

1. Is the classification automatic (Svetlazar's work) or is it 
DBA specified?

2. validation (Vassilis): should we validate a class by verifying 
that it makes sense (in general or in a particular database)