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Navigating nodes

for n in N():

The result of N() is a generator that walks through all nodes in the canonical order (see below). Iterating over N() delivers you all words and structural elements of your corpus in a very natural order.

Walking nodes

Most processing boils down to walking through the nodes by visiting node sets in a suitable order. Occasionally, during the walk you might want to visit embedding or embedded nodes to glean some feature information from them.

More ways of walking

Later, under Features there is another convenient way to walk through nodes.

canonical order

The canonical order is a way to sort the nodes in your corpus in such a way that you can enumerate all nodes in the order you encounter them if you walk through your corpus.

Briefly this means:

  • embedder nodes come before the nodes that lie embedded in them;
  • earlier stuff comes before later stuff,
  • if a verse coincides with a sentence, the verse comes before the sentence, because verses generally contain sentences and not the other way round;
  • if two objects are intersecting, but none embeds the other, the one with the smallest slot that does not occur in the other, comes first.
first things first, big things first

That means, roughly, that you start with a book node (Genesis), then a chapter node (Genesis 1), then a verse node, Genesis 1:1, then a sentence node, then a clause node, a phrase node, and the first word node. Then follow all word nodes in the first phrase, then the phrase node of the second phrase, followed by the word nodes in that phrase. When ever you enter a higher structure, you will first get the node corresponding to that structure, and after that the nodes corresponding to the building blocks of that structure.

This concept follows the intuition that slot sets with smaller elements come before slot set with bigger elements, and embedding slot sets come before embedded slot sets. Hence, if you enumerate a set of nodes that happens to constitute a tree hierarchy based on slot set embedding, and you enumerate those nodes in the slot set order, you will walk the tree in pre-order.

This order is a modification of the one as described in (Doedens 1994, 3.6.3).


Doedens, Crist-Jan (1994), Text Databases. One Database Model and Several Retrieval Languages, number 14 in Language and Computers, Editions Rodopi, Amsterdam, Netherlands and Atlanta, USA. ISBN: 90-5183-729-1, The order as defined by Doedens corresponds to walking trees in post-order.

For a lot of processing, it is handy to have a the stack of embedding elements available when working with an element. That is the advantage of pre-order over post-order. It is very much like SAX parsing in the XML world.


delivers an iterable of nodes as a tuple sorted by the canonical ordering.


An iterable of nodes to be sorted.

nodeList = sorted(nodes, key=sortKey)

A function that provides for each node the key to be used to sort nodes in the canonical ordering. That means that the following two pieces of code do the same thing:

sortNodes(nodeSet) and sorted(nodeSet, key=sortKey).

tupleList = sorted(tuples, key=sortKeyTuple)

Same as sortKey, but this one works on tuples instead of nodes. It appies sortKey to each member of the tuple. Handy to sort e.g. search results. We could sort them in canonical order like this:

sorted(results, key=lambda tup: tuple(sortKey(n) for n in tup))

This is exactly what sortKeyTuple does, but then a bit more efficient.


The node types are ordered in, and if you reverse that list, you get the rank of a type by looking at the position in which that type occurs.

The slotType has otypeRank 0, and the more comprehensive a type is, the higher its rank.