In the attached library you can find 6 different layouting algorithms for connected directed graph without cycles (≙ tree). All these algorithms are implemented on the principle of tree traversing. 

A) Radial Layout Algorithms
The traversion of the graph starts at the first level which is the source node. We follow the pointer to the next node table, and iterate through the nodes at that level. This is repeated for all levels until the end of the last node table is reached.
These algorithms are implemented and documented in 'Radial Tree Graph Drawing Algorithm for Representing Large Hierarchies' by Greg Book & Neeta Keshary (Link).

1) Radial Tree Layout - Simple

2) Radial Tree Layout - Complex

3) Radial Tree Layout - Complex incl. Wedges


B ) Tree Layout Algorithms
4) Directed Tree Layout - Horizontal


5) Directed Tree Layout - Vertical

6) Create tree from model information
Here, the algorithm reads the attribute 'Comment' and if there is a name of another object defined, then it creates an 'Edge'.

Attachments:

Directed Graph Layout Algorithms Library.abl (108.9k), ExampleModel 1.0.adl (31.8k)