Re: S.O.D.A. database Query API - call for comments

In article <9d99ik$reg$02$1_at_news.t-online.com>, Carl Rosenberger says...
>
>mikito Harakiri wrote:
>>
>> Object references in general are one-way only, right? Is it technically
>> impossible to directly navigate from detail to master, then. Find all
 purchase
>> orders with item #12 on the list.
>
>Object references are "one-way" on instantiated objects. The implementation
>of the abstract representation within the engine may vary. Indices can
>provide the same retrieval speed for "object constrained by parent" as for
>"object constrained by member".

Ok, let object Car contain Wheel (4 fields, actually:-). How exactly would I find a Car given a Wheel; what indexes would I use? (Note that sql folks are eager to provide exact sql statements -- I would like to see the code for objects either:-)

>How are keys modeled within a relational database? A foreign key is always
>one-way.

Foreign key is required to match unique key on master table -- in that sence it's assymmetric. From implementation perspective, however, indexes make it to look pretty much like bidirectional link.

>> Unless, oodb starts maintaining double-linked references, you can't claim
 that
>> it could easily match quering capability of relational. And adding
 double-linked
>> references to object model compromises the simplicity that object folks
 are
>> emphasising.
>
>An object-oriented link is alwas bidirectional:
>- An object has a member.
>- A member object has a parent.
>
>Although the programming languages provide no method to navigate the wrong
>way around, object database query optimizers have not problems in
>understanding this bidirectional reference.

Navigating the "wrong way" without maintaining "backward references" is something I always wanted when programmed in C++ and Java.

>I think you accidentally pointed to an advantage of object databases with
>your posting.
Received on Tue May 08 2001 - 20:28:41 CEST