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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: Historical Session
Date Mon, 21 May 2007 22:35:16 GMT
As I've had it explained to me, you would not choose the time in a  
user-generated or user-visible query. Instead, the user would set the  
time and associate it with an EntityManager. The time is invisible to  
normal entity operations, including queries. For each query for a  
temporal object (the terminology I've heard) the EntityManager would  
include the appropriate WHERE clauses into the SQL that would select  
the proper instances based on the time.

So a find by primary key, navigation, or query would have the  
appropriate WHERE clauses generated with no action on the part of the  
user.

In the example below, the A instance doesn't need to worry about  
which B it refers to, because the B instances corresponding to A's  
time are also selected automatically, in that both A and B have  
corresponding temporal WHERE clauses based on the same time.

Craig

On May 21, 2007, at 3:16 PM, Ricardo Andere de Mello wrote:

> yes.... this look something simple, but it is not...
> see, objects exists in time, so for example, they are not deleted,  
> they are
> "finalized".
> the worst part are the relationships, because they are historical  
> too...
> basically you have a start and end date for that object, and the  
> object with
> end date null is the actual object.
> everytime you modify an object you clone it, set the end date of  
> the old,
> and set the start date of the new.
> imagine now that "A" points to "B". both are historical objects. if  
> "B" is
> modified, a new historical object is created. "A" should point to  
> the new
> "B", not the old one. so you must have a "historical id" or a  
> "historical id
> object" to point at, that is common to all "B".
>
> []s, gandhi
>
> 2007/5/21, Marc Prud'hommeaux <mprudhom@apache.org>:
>>
>>
>> Something like: "select x from Employee x as x was on January 1,  
>> 2002"
>>
>>
>>
>> On May 21, 2007, at 11:01 AM, Kevin Sutter wrote:
>>
>> > Sorry to show my ignorance, but what are "historical objects"?
>> > Thanks!
>> >
>> > Kevin
>> >
>> > On 5/18/07, Ricardo Andere de Mello <wytwyg@gmail.com> wrote:
>> >>
>> >> ok, I'm sending this message to netmind list too, so they can
>> >> answer my
>> >> next
>> >> question too:
>> >>
>> >> * Maybe this is a silly question, but is it possible to place
>> >> netmind's
>> >> beankeeper historical structure between OpenJPA and the database
>> >> backstore?
>> >>
>> >> I dont think *any* serious commercial application can avoid
>> >> historical
>> >> objects.
>> >> I think netmind's beankeeper is a great thing, and JPA is a good
>> >> standard.
>> >> Mixing both projects would be very cool. ;-)
>> >>
>> >> []s, gandhi
>> >>
>> >>
>> >> 2007/5/18, Marc Prud'hommeaux <mprudhom@apache.org>:
>> >> >
>> >> >
>> >> > Sadly, no. We don't have any built-in support for historical
>> >> support
>> >> > at this time, although we have thought for a long time that this
>> >> > would be a great feature to have.
>> >> >
>> >> > You can, of course, do it yourself manually with a bunch of
>> >> > persistent Date fields, but I agree that this is pretty
>> >> cumbersome to
>> >> > have to manage yourself.
>> >> >
>> >> >
>> >> >
>> >> > On May 18, 2007, at 11:27 AM, Ricardo Andere de Mello wrote:
>> >> >
>> >> > > Does OpenJPA have something similar to TopLink's  
>> "AsOfClause" ?
>> >> > >
>> >> > > I've been working for some time with OJB and Hibernate, and  
>> I'm
>> >> > > work a lot
>> >> > > with historical objects.
>> >> > > It really sucks to manage lots of classes to build a  
>> historical
>> >> > > structure of
>> >> > > objects and object relations.
>> >> > >
>> >> > > Netminds beankeeper does a great job about this, but I'd  
>> like to
>> >> > > adhere to
>> >> > > JPA...
>> >> > >
>> >> > > Any idea of implementing historical objects AND RELATIONS,
>> >> inside JPA?
>> >> > >
>> >> > > --
>> >> > > Ricardo Andere de Mello
>> >> > > Presidente do Quilombo Digital
>> >> > > 55 (11) 3271-7928 / 55 (11) 9917-7722
>> >> >
>> >> >
>> >>
>> >>
>> >> --
>> >> Ricardo Andere de Mello
>> >> Presidente do Quilombo Digital
>> >> 55 (11) 3271-7928 / 55 (11) 9917-7722
>> >>
>>
>>
>
>
> -- 
> Ricardo Andere de Mello
> Presidente do Quilombo Digital
> 55 (11) 3271-7928 / 55 (11) 9917-7722

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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