[Versa] Issue 3

[Michael Olson]

On Aug 12, 2005, at 10:41 PM, Chimezie Ogbuji wrote:

> Along the lines of promoting subjects to first class Versa datatypes
> (and the problem of such a major change), I had the idea that perhaps
> you could maintain the current infrastructure but have a way to
> extract / project statements as a set of 3 item lists
> (subject,predicate,object) and have 3 functions for extracting the
> parts of the lists:
>
> subjects(x)  =>  map(x,'.[1]')
> predicate(x)  =>  map(x,'.[2]')
> objects(x)  =>  map(x,'.[3]')
>


My concern with this is that it lacks extensibility.  ie, 4Suite  
probably wants to make scope information availability in statements.   
Does this mean that 4Suite returns a triple of length 4?

Mike

> Consider a 'Statement Pattern' expression (different from a traversal
> operator) that allows you to extract statements (as a set of 3 item
> lists):
>
> {SPF SPF SPF} => set(list(s1,p1,o1),list(s2,p2,o2),list(s3,p3,o3),...)
>
> where SPF (statement pattern filter) is either an expression which is
> converted to a list which serves as a filter against the corresponding
> components (subject/predicate/object) of candidate statements.
> Statements are included only if the corresponding part is a member of
> the list.  SPF can also be '*' in which case it is a wildcard and no
> filtering is done for those components.
>
> So:
> A - B -> *     becomes  objects({A B *})
> all() |- B -> eq('foo')  becomes  objects({* B 'foo'})
>
> Such patterns can do everything traversal operators do now in addition
> to address the original *issue* of returning predicates.  My use of {
> .. } clashes with my earlier suggestion to use them as existential
> placeholders, but I'm quickly running out of grouping characters that
> are not used :)
>
> This is just an idea to allow statements to be visible to the Versa
> data core w/out breaking it's current infrastructure but perhaps
> Uche's example use o filter to retrieve the properties on a resource
> with a particular value solves the original problem and this isn't so
> neccessary.
>
> Just some food for thought
>
>
> On 8/12/05, Michael Olson <Mike.Olson at fourthought.com> wrote:
>>>> I guess I should have finished my thought.  Because of the above,  
>>>> then
>>>> it makes sense to have some syntactic sweetness (as long as it is  
>>>> not
>>>> molasses) for the first to cases (like we have).
>>>>
>>>> Maybe the answer is
>>>>
>>>> "statement(traversal expression)" and let the engine work this  
>>>> out....
>>>>
>>>> That would certainly let us stay at 1.0
>>>
>>> So it would then be
>>>
>>> object(statement(traversal expression)) etc.  ?
>>>
>>
>>
>> I misspoke here a little  I think traverse and filter would remain the
>> same.  statement() would become a magic function as you pointed out
>> below that can reconstruct the statement.  More likely the
>> optimizer/query engine would flag the traverse/filter to return the
>> entire statement.
>>
>> Maybe the simpliest solution for 1.0 compliance is to modify the
>> traverse and filter function calls.  An optional parameter that
>> specifies result types.
>>
>>
>> Mike
>>
>>> We could sneak around on this if we were desperate to keep it at 1.0,
>>> but I think it would be improper because it does change the semantics
>>> of
>>> a traversal expression.  Right now A -> B -> C returns a list of
>>> objects, and if statement() has usual function call semantics, I  
>>> don't
>>> know how it can reconstruct full statements from just each object.   
>>> If
>>> statement is more magic than a function, then we have changed the
>>> semantics of the <identifier> '(' <expr> ... ')' production.
>>>
>>> I think that technically either case still calls for a 2.0.  Or at
>>> least
>>> a 1.5 ;-)
>>>
>>>
>>> --
>>> Uche Ogbuji                               Fourthought, Inc.
>>> http://uche.ogbuji.net                    http://fourthought.com
>>> http://copia.ogbuji.net                   http://4Suite.org
>>> Use CSS to display XML, part 2 -
>>> http://www-128.ibm.com/developerworks/edu/x-dw-x-xmlcss2-i.html
>>> XML Output with 4Suite & Amara -
>>> http://www.xml.com/pub/a/2005/04/20/py-xml.html
>>> Use XSLT to prepare XML for import into OpenOffice Calc -
>>> http://www.ibm.com/developerworks/xml/library/x-oocalc/
>>> Schema standardization for top-down semantic transparency -
>>> http://www-128.ibm.com/developerworks/xml/library/x-think31.html
>>>
>> ---------------------------------------------------------------------- 
>> --
>> -----------------
>> Mike Olson                                                Principal
>> Consultant
>> mike.olson at fourthought.com                +1 720 253 4662
>> Fourthought, Inc.
>> http://Fourthought.com
>> PO Box 270590,                                       http://4Suite.org
>> Louisville, CO 80027-5009, USA
>> XML strategy, XML tools, knowledge management
>>
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>>
>>
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------------------------------------------------------------------------ 
-----------------
Mike Olson                                                Principal  
Consultant
mike.olson at fourthought.com                +1 720 253 4662
Fourthought, Inc.                                       
http://Fourthought.com
PO Box 270590,                                       http://4Suite.org
Louisville, CO 80027-5009, USA
XML strategy, XML tools, knowledge management