Prototype OO was Re: Inheritance/defaulting of attributes

[Meltsner, Kenneth J]

     [Apologies for jumping in from outside the document/XML community -- I
     was reading the archive and found this thread interesting.  An earlier
     attempt at sending this out failed, so this may be a duplicate as
     well.]

     The XML community may want to look at prototype-based object-oriented
     programming as an alternative to traditional class-instance objects.
     Prototypes allow the designer/user to create an object, change its
     properties, and then create new objects that inherit from the original
     prototype.  There's a lot more details, including a description of
     inheritance by delegation of methods/properties to parent prototypes,
     but it tends to be a more useful approach for objects that model real
     world objects -- my dissertation used a variant of prototypes to
     implement an object-oriented approach to simulation for chemical
     thermodynamics.

     Another useful approach might be to look into constraint-based OO.  In
     this approach, the relationships between objects can be described and
     manipulated, usually in both directions (i.e. if x.width + y.width =
     total.width, setting the total.width and x.width to new values will
     force a change in y.width as well).

     Finally, I was impressed with, but lost the references to, some work
     on "middle-out" modeling.  Basically, traditional classes are used to
     go from general classes (animals, mammals) to specific classes (dogs,
     beagles), and then the system permits class properties to be replaced
     to allow for Ralph, a beagle with three legs, etc.  A similar
     middle-out approach might be useful -- define a hierarchy of DTDs, I
     suppose, and then permit specific exceptions to override default
     properties.

     Here are the references for folks with extra time, if I'm not too
     off-topic.

     The classic prototype-based OO language developed at Sun:

     http://self.sunlabs.com/

     A prototype-based, C++, constraint-based user interface system:

     http://www.cs.cmu.edu/Groups/amulet/amulet-home.html

     A bunch of variants on constraint-based languages and systems,
     including Web layout:
     (The hierarchy of constraints is especially useful for systems with
     defaults and different constraint strengths)

     http://www.cs.washington.edu/research/constraints/

     Ken Meltsner



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