Package it.unimi.dsi.webgraph.labelling
Main classes implementing labelling for immutable graphs. A labelled immutable graph is a graph endowed with labels, on its arcs and/or on its nodes; currently, only arc labelling is implemented (since node labelling can be easily dealt with outside of the WebGraph framework, anyway).
Warning: this package is experimental.
Labels
A label is just an instance of a class implementing the Label
interface: essentially,
for maximum versatility, is a set of key/value pairs, where keys are strings and values can be essentially anything; in most simple cases,
though, labels will be made by a single key/value pair (and the key will be, of course, irrelevant).
All arcs of the same graph will have labels of the same class, and for this reason labels offer a Label.copy()
method that allows the prototype design pattern to be used.
The only requirement for the serialisation of labels is that every label can be written as a selfdelimiting bit sequence (via the
Label.toBitStream(it.unimi.dsi.io.OutputBitStream,int)
method); essentially,
two kinds of label exists: fixedwidth labels (that write themselves using always the same, fixed number of bits) or
variablewidth labels; you can know whether a label has fixed width or not by calling Label.fixedWidth()
(this method will return 1 if the width is variable).
As an example, singleattribute integer label classes are implemented, one using fixed width and another using γcoding.
Labelled graphs
An arclabelled immutable graphs is an
immutable graphs with labels on its arcs; it rewrites the immutable graphs methods
covariantly so that, for example, when one iterates on the successors of a node using ArcLabelledImmutableGraph.successors(int)
not a simple IntIterator
is returned (iterating over the nodes that are successors of the given node), but rather
a ArcLabelledNodeIterator.LabelledArcIterator
(that returns every time a node/label pair).
Even though different implementations of arclabelled immutable graphs
may exist, we provide one (BitStreamArcLabelledImmutableGraph
) that assumes that an immutable graph has been
provided and that labels have been written onto a label file in the same order as the arcs of the immutable graph would be returned by the
ArcLabelledImmutableGraph.nodeIterator()
method. An additional offset file must be provided that
allows one to know the offset (in bit) within the label file where the labels of the arcs going out of a given node start.
These data are generated using the store()
methods whose implementation is suggested in
the class documentation of ArcLabelledImmutableGraph.

Interface Summary Interface Description ArcLabelledNodeIterator.LabelledArcIterator An iterator returning successor and the labels of the arcs toward them.ArcRelabelledImmutableGraph.LabelConversionStrategy A way to convert a label into another label.Label A set of attributes that can be used to decorate a node or an arc of a graph.LabelMergeStrategy A way to merge two labels into one; the actual merge is performed by theLabelMergeStrategy.merge(Label, Label)
method.LabelSemiring A semiring used to compose labels. 
Class Summary Class Description AbstractIntLabel An abstract (singleattribute) integer label.AbstractIntListLabel An abstract (singleattribute) listofintegers label.AbstractLabel An abstract implementation throwing anIllegalArgumentException
on all primitivetype methods.ArcLabelledImmutableGraph An abstract implementation of a graph labelled on its arcs.ArcLabelledImmutableSequentialGraph An abstract arclabelled immutable graph that throws anUnsupportedOperationException
on all randomaccess methods.ArcLabelledNodeIterator An iterator returning nodes, their successors and labels on the arcs.ArcRelabelledImmutableGraph Exhibits an arclabelled immutable graph as another arclabelled immutable graph changing only the kind of labels.BitStreamArcLabelledImmutableGraph A labelled graph storing its labels as a bit stream.BitStreamArcLabelledImmutableGraph.BitStreamLabelledArcIterator FixedWidthIntLabel An integer represented in fixed width.FixedWidthIntListLabel A list of integers represented in fixed width.GammaCodedIntLabel A natural number represented in γ coding.IntegerLabelFilter A filter for labelled graphs preserving those arcs whose integer labels are in a specified set.Labels UnionArcLabelledImmutableGraph An arclabelled immutable graph representing the union of two given such graphs.