[bind10-dev] meta data source vs data source container (summary)

JINMEI Tatuya / 神明達哉 jinmei at isc.org
Tue May 8 00:15:02 UTC 2012

In the f2f meeting we discussed two options for implementing the
concept of "set of data source(client)s": A "meta data source
(client)", which will be a derived class of DataSourceClient, and a
separate "container" class that holds the set of data source(client)s.

This is a higher level summary of major pros and cons of these
approaches, which I promised to send to the dev list at the meeting
(I'm trying to be objective, but I'll be quite likely biased because I
have a clear preference):

- pro for "meta": existing code that uses abstract data source client
  interface won't have to be changed
- pro for "meta": existing code that instantiates data source clients
  using the polymorphic factory won't have to be changed (although in
  practice there's less such code right now).
- pro for "meta": the amount of code to be added will be smaller.  In
  particular, we won't need to add a python wrapper.
- pro for "container": the application can have finer control about
  the underlying set of data sources (such as iterating over them by
  itself to find a specific data source that matches complicated
- pro for "container": we will be able to extend the base client class
  more freely, without worrying about breaking the existing
  deployment.  It will also be possible to migrate to the "meta"
  approach with keeping compatibility.

There are other small differences, but overall, it seems to me to be
the choice between the initial implementation cost vs extendability.
The "meta" approach will require less code to complete from where we
are now.  But it will introduce another constraint in the base class
and will (possibly) limit some types of future extensions to the base
class; the container approach doesn't have this problem, and we can
switch to the meta approach later if it turns out to make more sense.

To keep this message (which is expected to have more readers) shorter,
I'll stop here for now.  I'll send another message for more detailed

JINMEI, Tatuya

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