Hierarchical Data Storage

[Bart Pietercil]

I think you responded to that in the next mail.

Data normalization leads to a "trees" table, the hierarchical table  
stores an extra pointer to the tree table and this enables you to  
store as many trees in the hierarchical table as necessary.

See ya

Bart

On 13-feb-07, at 10:30, Ruslan Zasukhin wrote:

> On 13/2/07 12:24 AM, "Bart Pietercil" <bart.pietercil at gmail.com>  
> wrote:
>
> Bart,
>
> Actually Trevor points that IF exists several ROOTs than this  
> algorithm
> simply may not work.
>
> Because you already cannot use
>     UPDATE WHERE  left > 1 and RIGHT < 32
>
> Because this UPDATE also will touch nodes of OTHER trees.
>
> Right Trevor?
>
> Hmm.
>
>
>> Yes, you are right
>>
>> The only moment where you can update the tree is when you can obtain
>> an exclusive read-write lock on the cursor "WHERE right >
>> my_current_right".
>> So this  code would need to be placed in a Try Catch  block.
>>
>> Maybe hard (depending on how you implement reading the tree), but
>> certainly feasable (I think).
>>
>> My solution requires a lot less updating of tree values, so I admit
>> that you need to be worried a lot more (lucky me)
>>
>> Bart
>>
>> On 12-feb-07, at 22:41, Trevor DeVore wrote:
>>
>>> On Feb 12, 2007, at 12:54 PM, Bart Pietercil wrote:
>>>
>>>> Hi Trevor,
>>>>
>>>> why wouldn't you organise it as Tree "lessons" ---> Node 1 Lesson
>>>> 1, Node 2 Lesson 1.1 Node 3 Lesson 2  and so one ?
>>>>
>>>> The Tree traversal method allows an unlimited number of Levels?
>>>>
>>>> Maybe I'm missing something (wouldn't be the first time)
>>>
>>> Hi Bart,
>>>
>>> In this particular db design lessons cannot have a parent lesson.
>>> Lessons are grouped into curriculums (which has a table of it's own
>>> as well).  So a lesson tree is just a single lesson and it's steps
>>> which is the combination of the lessons and steps table.
>>>
>>> I think in either case you are left with the same problem though.
>>> As I understand it, if you are going to have multiple people
>>> working on the database than how do you keep updates in on portion
>>> of the tree from affecting everything to the "right" of the current
>>> node?  It seems if you do change the left/right values for every
>>> record to the right of a node that any records other db editors
>>> might have open would be invalidated and have to be reloaded.
>>>
>
> -- 
> Best regards,
>
> Ruslan Zasukhin
> VP Engineering and New Technology
> Paradigma Software, Inc
>
> Valentina - Joining Worlds of Information
> http://www.paradigmasoft.com
>
> [I feel the need: the need for speed]
>
>
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