Re: [Xotcl] representing graphs in xotcl...

From: Shishir Ramam <sramam_at_gmail.com>
Date: Wed, 7 Nov 2007 07:37:04 -0800

Thanks Gustaf and Artur!

Not sure if this should be considered expected behaviour - but does the type
have to be defined before declaration?
This simple script illustrates the issue - see the last couple of attempts.

Class Base -slots { Attribute connects_to -multivalued true -type Base }
Class DerivedA -superclass Base -slots { Attribute connects_to -multivalued
true -type DerivedB }
Class DerivedB -superclass Base -slots { Attribute connects_to -multivalued
true -type DerivedA }

Base b
DerivedA da
DerivedB db

b connects_to add da
b connects_to add db

db connects_to add b
>>> can't set "connects_to": b is not of type DerivedA << This should be
expected. all A-ok.

db connects_to add da
da connects_to add b
>>> can't set "connects_to": bad class "DerivedB": must be alnum, alpha,
ascii, control, boolean, digit, double, false, grap
h, integer, lower, print, punct, space, true, upper, wordchar, or xdigit

da connects_to add db
>>> can't set "connects_to": bad class "DerivedB": must be alnum, alpha,
ascii, control, boolean, digit, double, false, grap
h, integer, lower, print, punct, space, true, upper, wordchar, or xdigit


On Nov 7, 2007 12:06 AM, Gustaf Neumann <neumann_at_wu-wien.ac.at> wrote:

> Shishir Ramam schrieb:
> > Hi,
> > I have a need to represent a directed graph in XoTcl.
> Here are two small examples for representing graphs
>
> In version one, edges are lists of references to nodes stored
> as attributes of nodes. By specifying "-multivalued true", it
> is possible to "add" or "delete" elements from the list.
> By using "-type Node" the code ensures, that only instances
> of Node may be added to the list, otherwise an error is thrown.
>
> Class Node -slots {
> Attribute connects_to -multivalued true -type Node
> }
>
> Node n1
> Node n2
> Node n3
>
> n1 connects_to add n2
> n1 connects_to add n3
>
> puts [n1 connects_to]
>
> A "destroy" of a nodes automatically destroys the
> edges as well, by refining the destroy method, one
> could as well destroy the referenced edges (similar
> to aggregation (nesting objects), but one has to be
> care about cyclical edges.
>
> Another approach is to define Edges as objects
> which makes it possible to provide methods for
> Edges and to store attributes in it.
>
> Class Edge -slots {
> Attribute from -type Node
> Attribute to -type Node
> }
>
> Edge e1 -from n1 -to n2
> Edge e2 -from n1 -to n3
>
> Simarly as above, when a dynamic graph
> is to be maintained, the destroy method of Node
> should care about deleting references in Edges
> to ensure referencial integrity.
> The easiest way is to check in the destroy method
> of Node all Edges with [Edge info instances], if
> their "form" or "to" attributes contain the node.
> One could as well build an index to make this
> operation faster for large graph via a constructor
> of Edge, which maintains e.g. a list of referenced
> edges per node (e.g. via multivalued attribute
> "references", similar to approach 1)
>
>
> -gustaf neumann
>
>

-- 
Don't worry about people stealing an idea. If it's original, you will have
to ram it down their throats.
 - Howard Aiken