Re: Organization hierarchy

You're right, the children property is not necessary at all in the protocol. 
It is an implementation mechanism I use it as a cache, in order to reduce the number of queries in the DB.

I agree with the proposed implementation, as shown in the ticket (the child_id refers to the current document).
I would add a current_parent_id property, though, just to keep compatibility with code using the standard parent_id representation for trees.

Guglielmo

Il giorno 06/set/2013, alle ore 20:43, James McKinney <james@opennorth.ca> ha scritto:

> Thanks, Guglielmo.
> 
> Is a "children" property necessary? It's possible to traverse a tree using only a "parents" property. It's a little more error-prone to have to maintain the organizational hierarchy in two fields instead of one.
> 
> I've created an issue in the tracker: https://github.com/opennorth/popolo-spec/issues/41
> 
> James
> 
> On 2013-09-04, at 5:53 AM, Guglielmo Celata wrote:
> 
>> I understand the *preoccupations* (forgive my limited english vocabulary) regarding the standard parent_id case, which indeed would cover 9 out of 10 use cases.
>> What we came up with in some of the projects is de-normalizing the database, and it's pretty much the solution you're proposing.
>> 
>> So, for example, the Organization model would still have a parent (or parent_id) attribute, that I would call current_parent, for clarity.
>> The JSON serialization explicitly would contain both an array of parents and children, with start and end dates, extracted from the external Relation model.
>> The current_parent would usually be the last element of the parents list, and it must have a Null end_date.
>> 
>> This would allow to represent time-dependend father-child compositions.
>> 
>> 
>> An example (pseudo-python) for an organization with parentships changing dynamically over time:
>> 
>> Organization
>>  { id: ID,
>>    current_parent_id: PID3,
>>    parents: 
>>    [
>>      { id: PID1, start_date: '2006/07', end_date: '2008/09/01' },
>>      { id: PID2, start_date: '2008/09/02', end_date: '2012/04' },
>>      { id: PID3, start_date: '2012/04', end_date: NULL },
>>    ],
>>    childresn: []
>>  }
>>     
>> 
>> 
>> 
>> As for N-N aggregations, it's a very rare use-case, in the institutional context we're focusing on, I can only think of 
>> a rather stretched example.
>> 
>> Since in Italy there is a minimum number of MPs required to form a group (in both chambers of the parliament), 
>> we have a so called mixed group, with members from various small (usually regional) electoral parties.
>> Now, from time to time, an MP exits from a big group and enters into the mixed group, usually a few months before
>> passing into another different big group alltogether, just in order to disguise the actual flip.
>> 
>> If I want to know the composition of the mixed group at any given time, in terms of electoral parties, a single party could easily be into two groups.
>> The electoral party as an organization exists independently of the parliament groups.
>> 
>> Of course I could just count the memberships and obtain the same result, but I was just trying to make an example.
>> In other contexts these situation could arise more frequently.
>> 
>> I would agree in considering aggregation issue a minor one.
>> Given the focus and context of the popolo project, it could be left out of the specs.
>> 
>> 
>> Guglielmo
>> 
>> 
>> 
>> Il giorno 04/set/2013, alle ore 00:46, James McKinney <james@opennorth.ca> ha scritto:
>> 
>>> Hi Guglielmo,
>>> 
>>> For your second question about aggregations (N-N relations between organizations), can you give an example from your work where this is the case?
>>> 
>>> For the first question: indeed, there is an issue in the tracker: https://github.com/opennorth/popolo-spec/issues/27 Very few existing standards handle changes over time, so we will likely have to come up with our own solution like the one you suggest.
>>> 
>>> The relation you propose would work. It's actually very similar to a Membership in Popolo. (Perhaps an eventual solution would have a Relation superclass with your new class and Membership as subclasses.)
>>> 
>>> The challenge when dealing with historical use cases is to make sure that the common use cases are still easy to implement. Here, a common use case is to represent the *current* organizational hierarchy/tree/graph. There already exist many treelibraries in various languages for storing tree structures in databases. Most of these have no method of tracking changes over time, and use a single field like "parent_id" to track the tree structure. An ideal solution to the challenge would allow people to continue to use such libraries.
>>> 
>>> Perhaps a solution would be to maintain "parent_id" and "parent" as-is, and to add a new "parents" property, whose value is an array of Relation objects? Implementations can then choose whether to implement either "parent_id" or "parents" or both.
>>> 
>>> Depending on how the aggregations issue is resolved, it may make sense to encourage the use of "parents" only.
>>> 
>>> Would anyone be against eliminating parent_id, if that were part of a solution?
>>> 
>>> James
>>> 
>>> On 2013-09-03, at 9:38 AM, Guglielmo Celata wrote:
>>> 
>>>> James,
>>>> the Popolo protocol currently allows hierarchical relations between organizations to be mapped through the parent_id attribute.
>>>> 
>>>> One possible shortcoming is that this is a permanent relation (it has no start nor end dates), and sometimes, especially in political groups, relations do depend on time.
>>>> 
>>>> Another lesser shortcoming is it maps compositions (a group, or a big company and its departments), but leaves out aggregations (members can join more than one group).
>>>> 
>>>> In a relational world, I would map it with an external entity:
>>>> 
>>>>     ------------
>>>>   1|            |N
>>>>  -----        -----
>>>> | Org |------| Rel |
>>>>  ----- 1    N -----
>>>> 
>>>> Where Rel is the relation and it would have these fields:
>>>> id
>>>> from_id
>>>> to_id
>>>> start_date
>>>> end_date
>>>> 
>>>> from_id and to_id are references to the Org, organizaiton entities.
>>>> 
>>>> Don't know how it would translate into the protocol and if the complexity it introduces are worth the issues it tries to solve. 
>>>> 
>>>> 
>>>> Any ideas?
>>>> 
>>>> Guglielmo Celata
>>>> Developer
>>>> Associazione Openpolis
>>>> 
>>> 
>> 
>