Wednesday, October 22, 2008

Silver Bullet: Model the world, not the application

DISCLAIMER: Ok, I admit it...this is cut/pasted directly from my brain fart notebook, i.e. not ready for prime time...but dammit Jim, its just a blog!

In the arsenal needed to fight unsuccessful software development projects, it will take a whole clip full of silver bullets.  One of those silver bullets, I believe, is more accurately modeling the world using knowledge of Philosophy.

There is a great struggle between getting everything "right" up front,  versus, doing "just enough" specification and design.  When trying to balance "make it flexible" in order to support future re-use, versus XP mandates like "don't design what isn't needed today", it is hard to know (or justify) where to draw the line.  Due to "changing requirements", those "flexible reuse" features (that were merely contingent at design time) are often mandatory before the original development cycle is even complete.

WELL, lots of requirements don't change THAT much if you are modeling correctly in the first place.

Humans haven't changed appreciably in millennia, even if the roles they play do.  So, if "humans" are modeled separately from "employees", it is that much less work when you later need to integrate them with "customers". [Theme here is "promote roles programming", the justification of which is made more obvious when taking essentialism to heart.]

In general, the foundation of one's data/domain/business/object/entity-relationship model is solid and unchanging, if all "domain objects", "business objects", etc are modeled based on a clear understanding of the essential versus accidental aspects of the "real world", and NOT based on the requirements description of a particular computer system or application.  Modeling based on "just what is needed now according to this requirements document today" is too brittle, both for future changes, and especially for integrating with other systems and data models.

After all, adding properties and relationships to entities is fairly easy if the entities themselves are correctly identified.  It is much harder to change the basic palette of entities once a system design is built upon them.  Also, all the more reason to be sure and not confuse entities with roles they can take on.

Example: I don't have to wonder who I might have to share employee data with if I realize that an "employee" is actually just a role that a person takes on.  If I model the essentials of the person separately from the attributes of the employee role, it will be much easier to integrate that data with, say, a "customer" database later.  If the customer data model recognizes that "customer" is just a role that a person takes on, its Person table is much more likely to be compatible with my Person table than would be the case with my naive Customer and their Employee tables (and still other Patient tables, etc, etc.)

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