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RE: [xp] Metadata

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  • Steven Gordon
    I have used XML property, configuration, or preference files effectively in many OO projects. I consider this to be metadata, because it is not data that the
    Message 1 of 3 , Apr 30, 2004
      I have used XML property, configuration, or preference files effectively in many OO projects. I consider this to be metadata, because it is not data that the system processes, but rather data that tells the system how to behave.

      I develop this kind of metadata iteratively by:
      - starting out using constants (or their equivalents) instead of literals in my code.
      - turning those constants into getters on a shared object when it reduces code duplication (by allowing the same class to serve multiple masters by passing the shared object as a parameter to the class or its factory method).
      - persisting that shared object appropriately when required to (usually near the end of a release, when pragmatic operational issues become a higher priority than pure business functionalities). Persisting the shared objects as local XML files is usually the most expedient solution, but sometimes the information has to be accessible from multiple platforms, so a database is a pragmatic choice. Many customers have a strong preference to use their already existing relational database as compared to having another kind of database to maintain, so the technical advantages of object databases rarely overcome the pragmatic disadavantages.

      Steven Gordon

      -----Original Message-----
      From: Victor Goldberg, Ph.D. [mailto:vmgoldberg@...]
      Sent: Thu 4/29/2004 9:04 PM
      To: extremeprogramming@yahoogroups.com
      Cc:
      Subject: [xp] Metadata



      It is a few years I have been hearing about Metadata, but I never saw
      anything practical coming out of it, in terms of application development in
      a real OO project. I am glad I didn't see any discussion promoting the
      subject here. Nevertheless, I would like to start a little discussion in a
      brainstorming mode, just to see if we are in agreement with my ideas, or if
      not, maybe I can learn something.

      In my view, the term metadata refers to both the structure of data and the
      structure of data relationships to other data. By doing OO design we are
      implicitly dealing with metadata, and by practicing XP we are continuously
      improving the organization of the metadata structure. This is even more
      implicit if we are using Smalltalk or Python. OO in general and dynamic
      typing languages in particular take care of the metadata considerations,
      freeing the developers from having to deal with these issues.

      I have seen people (architects(?)) still stuck to metadata considerations.
      This is especially necessary when using XML.

      So, my thought is that unless you need to communicate between otherwise
      incompatible systems, don't use XML or a relational database. Use an OO
      database. Otherwise, you are building a system first, then you are
      deconstructing it, then rebuilding it again. It sounds like a waste of
      resources to me.

      Any comments?

      Victor



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