OO Principles

Hi! Today I am reading the book Head First Object-Oriented Analysis and Design, I specially liked the OO Principles, I have already read about them in c2, but I really like the way they are summarized in this book:

• OCP: Classes should be open for extension, but closed for modification. (to avoid new requirements breaking old tested code)
  
• DRY: Don't repeat yourself, avoid duplicate code by abstracting out things that are common and placing them in a single location. (to avoid having to fix the same thing in different places, or solving the same problema again, and again and again... I believe this is releated to YAGNI balances OAOO.... i guess I could say that YAGNI balances DRY, and therefore DRY equals OAOO)
  
• SRP: Single responsability principle, every object in your system should hava a single responsibility, and all the object's services shoul be focused on carry in out that single responsability. (to avoid Big Ball of Mud, a huge object that does everything, that is hard to extend, hart to understand, and lots of stupid little object that do nothing, mmmm, this reminds me of a pricinciple I read about a long time ago about balancing the intelligence between your objects)
  
• LSP: Subclasses should be suitable for their base clases (to avoid confusing code, on which you believe you can use a member of class hierarchy, and after trying you realize thet the result is not the expected one)
  

Objecthood!

According to the wikipedia, objecthood is: "is the state of being an object." I particularly liked that article, specially the part that says that:

"Theories of objecthood address two problems: the change problem and the problem of substance."

The answer to change problem is the answer to the following question, if object manifest themselves as cluster of properties... if you remove all the properties... what remains? According to substance theory, the answer is a substance (that which stands under the change)... if we apply this to Object Relational mapping... then.. the objectId (primary key) is the substance? Could this be used as a philosophical justification for the immutability of the primary key?

Then the text in the wikipedia continues: "Because substances are only experienced through their properties, a substance itself is never directly experienced." Is that a justification for never using the id (keeping it private)? Of course, there is another theory, the theory that since substance can not be experimented... then it doesn't exist, that is the "bundle theory".

In bundle theory all objects are merely a cluster of their properties and therefore... everything changes always... and no such thing as object ids/ primary keys really exist in the real world. This has an impact in relationships too, because we usually define a relationship as something that binds together 2 or more objects (at their substance level?)... but since object's substance doesn't actually exist then there isn't such thing as a "relationship" between two objects..

According to this relationships can only exist as something defined at the "property cluster level".. two (or more) objects aren't really related at the substance level... they simply "share a property" (is that why in SQL there isn't a way to make queries taking advantage of the integrity relationships? is "shared property" a better name for integrity relationships?)

And the thing gets worse: "Whether objects are just collections of properties or separate from those properties appears to be a strict dichotomy. That is, it seems that objects must be either collections of properties or something else." Is that the philosophical foundation for the "object/relational impedance mismatch"?

It seems that the conflict between a relational (bundle theory) and object (substance) worldview is there since way before a relational database or an object oriented language was invented...

I wonder what else could I learn from reading about this philosophical theories... (could there be a third one? is there a software programming paradigm for it?)

OMG: Object Orientation and Stored Procedures

OMG! how many times have I read the argument "using stored procedures is object oriented programming" just think of the database as an object, and think that each stored procedure is an method of the database....
Now... I am not going to say that using stored procedures is wrong... and I am not going to say that the only correct way of solving software problems is using object orientation... ( I do prefer to use object orientation, I a do prefer to use an object relational mapper instead of a stored procedures, specially for OLTP applications, I think application built that way are more maintainable, more portable between database, can be built faster, scale better, etc,etc)

But for batch processing, stored procedures have a clear advantage, and in my experience many business problems are solved by using an OLTP application, and a short but very important list of batch process... (of course the problem here is that if you built you application using an ORM, probably you have a lot of you business logic already implemented in a presentation-independent form, and, depending on the size of you database, you could program you batch process using your business objects... that has its disadvantages (slower performance that stored procedures) and its advantages (reutilization)... I believe reutilization and maintenance are more important that performance... specially because it is possible to worry about performance in the wrong way: for example Premature Optimization )

But the main point of this post, is that, first, I didn't think that using stored procedures was object oriented programming... it was "procedural programming"... or perhaps even "relational programming" but certainly not object oriented programming (where is the inheritance? where is the polymorphism?) but... after giving it some more thought... I realized that while it could not be "object oriented" it could be "object based"... stored procedures can encapsulate your tables (one of the major advantages of stored procedures) and you can see them as methods to a your "database" object...

So... now... your (OLTP?) system is a thin presentation layer on top of the "database object"... now... is there something in favor... or against that in object oriented design theory?.... mmm.... it achieves Presentation/Business Logic separation... and that is good... but I still feel there is something that doesn't feel right...

OMG! Well, it turns out there is! : Now the database is a God Object.
From Wikipedia: A God object is an object that knows too much or does too much. The God object is an example of an anti-pattern, it goes against divide & conquer ... using a God object is analogue of failing to use subroutines in procedural programming languages, because so much code references it, it makes maintenance difficult...

So... the next time someone tells you that using stored procedures is good object oriented programming... you could answer him or her: Oh My God (Object)! (You could think of it as object based, but, form an object oriented point if view.. it is a recommended solution? couldn't it be seen as an anti-pattern? I am not saying it is wrong, I am just saying that from an object oriented point of view, it might not be the best way to solve the problem... of course, using object orientation might not be the right way to solve this particular problem, after all, object orientation is not a Silver Bullet)