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I'm modeling an app which will let users look for real estate properties. So it's going to be a website where users will be able to look for rentals and sales on houses, flats, castles, grounds, shops, parkings, offices. According to that, I'm hesitating in the class diagram. Should I generalize all the type of real estate properties, written above, from the class RealEstateProperty or should I just associate to it a class TypeOfRealEstate, knowing that the type "Ground" for example can be as well a real estate property as the ground of a property like a House or a Castle. Also a parking can be a real estate property as well as a parking of a House.

Anyone has an idea of what's the best way to do that ? Thanks in advance.

Hubert Solecki
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  • Draw both designs (e.g. on [GenMyModel](http://www.genmymodel.com/)) and publish it here for us to give some ideas which one is better (:) – xmojmr May 26 '14 at 10:36

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It depends of what features of different RealEstates your system has to implement. A class's features include attributes, methods and associations.

  1. If all your potential RealEstates have same features, for example ID, type, price, date and responible agent, and you don't need to firther differenciate among them, than the associated type will do the work. Model RealEstateType as an Enum (or even class, if you expect to add new types) and associate it to a single RealEstate class.

  2. If different RealEstates, on the another extreme, need to have different features, you will need to inherit those from the base abstract class. For example, Ground have an attribute "area", while building has "number of floors". Even methods can be different, or associations.

Following your example, you would like to link Ground to House. This is much cleaner in the second version - just an association between Ground and House class. In one-class version, you would have to link the RealEstate with itself and add spacial restrictopns (very "ugly" design).

In summary, try to think about the features of different RealEstates and make your RealEstate hierarchy based on their differences.

You can end up with a single class or several dozens of them. :) Try to keep this hierarchy as simple as possible (less classes), but enough to mark their different features clarly.

Aleks
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