The name is derived from the Norse concept that the world is built on a giant tree, whose branches are so long they extend to the tree's roots. It is the brainchild of [Sean Deely Woods], and is presently implemented in [incr tcl]. Any other object system could be use, or none.

The actual implementation is closer to organic chemistry than cosmology. By devising a standard set of methods and expected behaviors, one can create a way to improve how programs snap together.

Yggdrasil splits the world into 2 types of objects: Containers and Nodes.

Containers implement 2 methods:
 * locate {address} - Convert a name like foo.bar.baz to a node id number
 * spawn object {node_id} - Return an object handle for a node id number

Nodes are assumed to contain an internal "array" of sorts. The Get and Set functions retrieve and overwrite values from that "array".
 * Get {fieldlist} - Works like array get. Return the entire internal state if fieldlist is blank
 * Set {field value ...} - Works like array set.
 * Links {type} - Return a list of nodes this object is linked to. If type is given, restrict the search to a certain type of link.
 * References {type} - Return a list of nodes that link to this object. Note, this only covers links within the same container.

Addressing
Nodes may be refered to in 4 different notations:

 * container foo.bar.baz - A list of 2 elements. Element 1 is the name of a container, element 2 is a string.
 * container int - A list of 2 elements. Element 1 is the name of the container. Element 2 is an integer node_id number.
 * foo.bar.baz - A single string. The container is assumed to be the same as the node.
 * int - An integer object number. The container is assumed to be the same as the node.

As a habit, all public facing methods should use the 2 element notation.

Link and references return data in the form of {{node_id link_name link_type} ...}

Special rules for Get and Set
Get returns a {field value} list. There is a special exception for when Get is asked for a single value. In that case it returns a single value. If any value is returned as an empty list is us assumed to be NULL or does not exist.

If the value of any field in a Set command is an empty list, the object converts the value to NULL or deletes the value from a hash table.

Yggdrasil is part of the [ODIE] package. More information is available at http://www.etoyoc.com/odie

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