penman.layout

Interpreting trees to graphs and configuring graphs to trees.

In order to serialize graphs into the PENMAN format, a tree-like layout of the graph must be decided. Deciding a layout includes choosing the order of the edges from a node and the paths to get to a node definition (the position in the tree where a node’s concept and edges are specified). For instance, the following graphs for “The dog barked loudly” have different edge orders on the b node:

(b / bark-01           (b / bark-01
   :ARG0 (d / dog)        :mod (l / loud)
   :mod (l / loud))       :ARG0 (d / dog))

With re-entrancies, there are choices about which location of a re-entrant node gets the full definition with its concept (node label), etc. For instance, the following graphs for “The dog tried to bark” have different locations for the definition of the d node:

(t / try-01              (t / try-01
   :ARG0 (d / dog)          :ARG0 d
   :ARG1 (b / bark-01       :ARG1 (b / bark-01
      :ARG0 d))                :ARG0 (d / dog))

With inverted edges, there are even more possibilities, such as:

(t / try-01                (t / try-01
   :ARG0 (d / dog             :ARG1 (b / bark-01
      :ARG0-of b)                :ARG0 (d / dog
   :ARG1 (b / bark-01))             :ARG0-of t)))

This module introduces two epigraphical markers so that a pure graph parsed from PENMAN can retain information about its tree layout without altering its graph properties. The first marker type is Push, which is put on a triple to indicate that the triple introduces a new node context, while the sentinel POP indicates that a triple is at the end of one or more node contexts. These markers only work if the triples in the graph’s data are ordered. For instance, one of the graphs above (repeated here) has the following data:

PENMAN                 Graph                            Epigraph
(t / try-01            [('t', ':instance', 'try-01'),   :
   :ARG0 (d / dog)      ('t', ':ARG0', 'd'),            : Push('d')
   :ARG1 (b / bark-01   ('d', ':instance', 'dog'),      : POP
      :ARG0 d))         ('t', ':ARG1', 'b'),            : Push('b')
                        ('b', ':instance', 'bark-01'),  :
                        ('b', ':ARG0', 'd')]            : POP

Epigraphical Markers

class penman.layout.LayoutMarker

Bases: penman.epigraph.Epidatum

Epigraph marker for layout choices.

class penman.layout.Push(variable)

Bases: penman.layout.LayoutMarker

Epigraph marker to indicate a new node context.

penman.layout.POP = POP

Epigraphical marker to indicate the end of a node context.

Module Functions

penman.layout.interpret(t, model=None)

Interpret tree t as a graph using model.

penman.layout.configure(g, top=None, model=None, strict=False)

Create a tree from a graph by making as few decisions as possible.

penman.layout.reconfigure(g, top=None, model=None, strict=False)

Create a tree from a graph after any discarding layout markers.

penman.layout.has_valid_layout(g, top=None, model=None, strict=False)

Return True if g contains the information for a valid layout.

Having a valid layout means that the graph data allows a depth-first traversal that reconstructs a spanning tree used for serialization.