# Redux: Circular Imports (Tim Cook)

**Category:** [Implementers (archive)](https://discourse.openehr.org/c/implementers-archive/158)
**Created:** 2008-07-04 01:18 UTC
**Views:** 9
**Replies:** 0
**URL:** https://discourse.openehr.org/t/redux-circular-imports-tim-cook/12907

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## Post #1 by @Max_Young

There's nothing wrong with a class defining a reference to another \(or
the same\) instance of that class \- that's how most hierarchical OO
implementations would work\.
I don't know Python \- but other languages certainly won't worry about
this \- it's not a circular reference in as much as the reference is \(at
run time\) to an instance of a class of the same type which may be the
same object, but generally would not be\.

In the case of the thumbnail attribute it does mean a thumbnail can have
a thumbnail can have a thumbnail, for example \- not likely but possible
in the model\. Not circular but hierarchical\.

For storing/retrieving there then needs to be implemented some mechanism
for 'walking' the structure from object to object \- and if there is a
circular reference there, it needs to be dealt with \(usually by flagging
each object as it is dealt with\)

I'm not sure I read your email right, though \- as you said you defined
ontology in IArchetype? Maybe I'm missing some Pythonism but I would
have had IArchetypeOntology implementing IArchetype, and
ArchetypeOntology implementing IArchetypeOntology

Eg in C\#
    public interface IArchetype
  \{\}
  public class Archetype : IArchetype
  \{\}
  public interface IArchetypeOntology : IArchetype
  \{
    Archetype ParentArchetype \{ get; set;\}
  \}
  public class ArchetypeOntology : IArchetypeOntology
  \{
    private Archetype  parentArchetype;
    public Archetype ParentArchetype
    \{
      get
      \{
        return parentArchetype;
      \}
      set
      \{
        parentArchetype = value;
      \}
    \}
  \}

And I can have

      Archetype a = new Archetype\(\);
      ArchetypeOntology b = new ArchetypeOntology\(\);
      b\.ParentArchetype = a;

Sorry if I have missed the point entirely \- my first post;

Max

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**Canonical:** https://discourse.openehr.org/t/redux-circular-imports-tim-cook/12907
**Original content:** https://discourse.openehr.org/t/redux-circular-imports-tim-cook/12907