extend_DAG

TODO: See also DAG_extension - should it be merged here?

Intro

This doc shows examples how default state DAG can be extended.

It uses:

• Lowercase letters (e.g.) a are used for state names.

• Uppercase letters (e.g.) A are used for class implementing the state.

Normally, they are closely related (e.g. a ~ A) because states have their meaning and that implies specific dependencies. In other words:

• implementation A of state a assumes it implements nothing else but a and depends on states b, c, ...

• implementation Z of state z assumes it implements nothing else but z and depends on states x, y, ...

But it is not always the case. For example, see below (replace by new and use old)

Case: trivial extend only

Let's say state c implemented by class C is the default target:

        graph TD
    a["a(A)"]
    b["b(B)"]
    c["c(C) / default target"]

    a --> c;
    b --> c;
    

Extend it by state d implemented by class D and make d the default target:

        graph TD
    a["a(A)"]
    b["b(B)"]
    c["c(C)"]
    d["d(D) / default target"]

    a --> c;
    b --> c;
    c --> d;
    

Case: replace only

Let's say state c implemented by class C has to be replaced:

        graph TD
    a["a(A)"]
    b["b(B)"]
    c["c(C)"]
    d["d(D)"]

    a --> c;
    b --> c;
    c --> d;
    

Instead, c has to be implemented by class X:

        graph TD
    a["a(A)"]
    b["b(B)"]
    c["c(X)"]
    d["d(D)"]

    a --> c;
    b --> c;
    c --> d;
    

Other cases

• replace_by_new_and_use_old