Re: [xml-dev] What is Data?

[Frank Manola <fmanola@acm.org>]

On Sep 2, 2009, at 5:34 PM, Peter Hunsberger wrote:

> On Wed, Sep 2, 2009 at 11:31 AM, Frank Manola<fmanola@acm.org> wrote:
>>
>>>
>>> The big difference is that RDF should be mostly all inclusive;
>>> metadata (well at least partial), relationships and data all laid  
>>> out
>>> in one (or two if you count the schema) place.  You won't see that  
>>> big
>>> picture with a DBMS.
>>
>> You say RDF *should* be mostly all inclusive.  Should I infer that  
>> you think
>> it isn't?  If so, in what way?  What are some examples?
>
> The difficulty in putting mixed content into it is perhaps the most
> glaring. However consider things like complex datatypes, sets or
> arrays.  You might be able to express them in RDF but instance data
> would be very painful.

I think I understand (and the situation is similar in a relational  
DBMS).  Much of the pain is caused by the requirement to make all the  
relationships (e.g., between the cells of the array) explicit in  
"pure" RDF.  If you can just store arrays as arrays (e.g., as the  
value of an "array" datatype), it's simpler, with the tradeoff that  
you need mutual understanding of what an "array" is to get at the  
elements someone else has created. You can do datatypes like that RDF  
too.  It's a matter of choosing how much mechanism you want to build  
into datatypes and how much you want to expose as "RDF".

>
>> I also don't understand what you're saying about the "big picture"  
>> you don't
>> see with a DBMS.  LIke what?  Is it that there's stuff you *can't*  
>> put in
>> the database, or stuff that people typically *don't* but in the  
>> database?
>
> Getting at the metadata of an RDBMs requires a separate operation from
> extracting the data.
>
> If I hand you a file representing some database (to the extent that is
> possible) then, at best, it's an opaque blob until you query it's
> schema (assuming you have the right tools).  From there you might be
> able to make some rational queries against the actual data.
>
> If I hand you a file that is RDF you can examine it directly (albeit,
> painfully) in any text editor you might choose (assuming it can handle
> the encoding).
>

Got it.

> -- 
> Peter Hunsberger