Inheritance/defaulting of attributes

[Sean Mc Grath]

A small amount of a modern OO language can go a long way towards
providing a mechanism for wielding inheritance with SGML element types
and spitting out 8879 DTDs.

Just for fun, I doodled this in Python. N.B. this idea can be taken
a *whole* lot further. Also, I'm sure Perl5, Java etc. can be wielded
similarly.

# Declare a class "Animal" derived from ElementType
class Animal(ElementType):
        def __init__(self,gi):
                ElementType.__init__(self,gi)
                # All Animals have legs
                self.attrs["LEGS"] = ("NUMBER","#REQUIRED")

# Declare a class "Dog" derived from "Animal"
class Dog(Animal):
        def __init__(self,gi):
                Animal.__init__(self,gi)
                #Some dogs have Rabies
                self.attrs["RABIES"] = ("(YES,NO)","#REQUIRED")

# Create Animal and Dog element types, printing out the attribute list
declaration
print Animal("MyAnimal")
print Dog ("MyDog")


This script prints :-

<!ATTLIST MyAnimal
        LEGS NUMBER #REQUIRED>
<!ATTLIST MyDog
        RABIES (YES,NO) #REQUIRED
        LEGS NUMBER #REQUIRED
>


The bass class "ElementType" is just this:-

class ElementType:
        def __init__(self,gi):
                self.attrs = {}
                self.gi = gi

        # Method to print self
        def __repr__(self):
                res = "<!ATTLIST " + self.gi
                for (Name,(DeclaredValue,DefaultValue)) in self.attrs.items():
                        res = res+"\t"+Name+" "+DeclaredValue+"
"+DefaultValue + "\n"
                res = res + ">"
                return res

Sean Mc Grath
sean at digitome.com
www.digitome.com



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