Data Model:

[Peter Otten]

Anthony wrote:

> On Apr 12, 7:46 pm, Aaron Watters <aaron.watt... at gmail.com> wrote:
>> On Apr 12, 10:14 pm, Anthony <alantho... at gmail.com> wrote:
>>
>>
>>
>> > I'm struggling on whether or not to implement GroupItem (below) with
>> > two separate models, or with one model that has a distinguishing key:
>>
>> > Given:
>> > class ParentGroup:
>> > a group of values represented by class GroupItem
>>
>> > class ChildGroup:
>> > a group of values represented by class GroupItem
>> > foreign-key to ParentGroup (many Children sum to one Parent)
>>
>> > Option A:
>> > class GroupItem:
>> > foreign-key to ParentGroup
>> > foreign-key to ChildGroup
>> > GroupItemType in (ParentItem, ChildItem)
>> > value
>> > value-type
>>
>> > Option B:
>> > class ParentGroupItem
>> > foreign-key to ParentGroup
>> > value
>> > value-type
>>
>> > class ChildGroupItem
>> > foreign-key to ChildGroup
>> > value
>> > value-type
>>
>> > What are my considerations when making this decision?
>>
>> > Thanks!
>>
>> It looks to me that the two designs
>> might be useful for different
>> purposes.  What are you trying to do?
>>
>> -- Aaron Watters
>>
>> ====
>>
whiff.sourceforge.nethttp://aaron.oirt.rutgers.edu/myapp/root/misc/erdTest
> 
> The group values represent statistics that I'm tracking, based on
> activity groups.  Some samples:
> 
> Group: Johnson, Total Units Produced = 10, Total Units Consumed = 5
> Chris Johnson, Units Produced = 6, Units Consumed = 3
> Jim Johnson, Units Produced = 4, Units Consumed = 2
> 
> Group: Smith, Total Units Produced = 15, Total Units Consumed = 8
> Mark Smith, Units Produced = 7, Units Consumed = 5
> Bob Smith, Units Produced = 8, Units Consumed = 3
> 
> The groups will be responsible for entering their own statistics, so I
> will have to do some validation at data entry.  The ability to create
> new statistic types (e.g. Units Broken) for new groups in the future
> is important.
> 
> What would be the advantages of using option A versus option B?

I may be missing something, but your example looks more like option C:

class Group:
    name

class Member:
    group # foreign key to Group
    name

class Item:
    member # foreign key to Member
    type
    value

You can calculate the totals for members or groups on the fly; the classical
tool would be a relational database.

Peter