Re: [ELPA] Package proposal: EBDB

[Roland Winkler]

> The ability to make BBDB extensible in future without requiring
> core changes is definitely a positive thing.

I agree, using, e.g., country-specific libraries can be a great way
of extending EBDB.  But this can also cause problems:

- Writing country-specific libraries for EBDB can be a fair bit of
  work.  Someone may develop a library for country XYZ up to the
  point "it works for me".  With the complexity of EBDB the
  developer may not notice / not care that some "irrelevant"
  features do not work.  When other users want to use the library,
  they can be stuck.

- Yet worse: "plain" users may have some records from country XYZ in
  their database, using the EBDB library for XYZ.  At some point,
  the very core of the EBDB code base may get updated in a way that
  also requires an update of the country-specific EBDB libraries.
  But the maintainer of the XYZ library may have disappeared from
  the stage for whatever reason.  What can the users do?  The EBDB
  database of a user might become unusable if its XYZ part cannot be
  read anymore.

  The opposite is also possible: It may turn out that it would be
  nice to update the EBDB code base in a way that also requires an
  update of the EBDB country-specific "add-on libraries" (or any
  other add-on libraries handling certain new fields for EBDB).  If
  there are many such country-specific add-on libraries out in the
  wild, it may become difficult to update the EBDB code base without
  breaking EBDB for many users.

  (Having developed BBDB for some time, I find it hard to predict
  when the code base of BBDB may have reached a level of maturity
  that allowed me to exclude the possibility of any further
  upgrades, say, in the format of the BBDB database files.  Then I
  am glad that such updates of BBDB can include the code to migrate
  the BBDB database files of the users.)

  (BBDB allows the user to customize the handling of addresses in a
  country-specific way; but this does not affect what is being
  stored in the database file using a universal, country-independent
  format.)

- In the worst case, also legal problems may arise: it may not be
  possible that someone else updates the code for the XYZ library.
  (But I am not a lawyer who could predict the details of such
  scenarios.)

I guess that to some extent these are generic aspects of an
object-oriented programming model, which is something I am less
familiar with in such a context.  Maybe others can comment.

It is certainly a [EB]BDB-specific issue that any code development
needs to keep in mind that many users already bring along their
database files.