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From vasia <...@git.apache.org>
Subject [GitHub] flink pull request #2984: [FLINK-5311] Add user documentation for bipartite ...
Date Mon, 12 Dec 2016 09:28:26 GMT
Github user vasia commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2984#discussion_r91908511
  
    --- Diff: docs/dev/libs/gelly/bipartite_graph.md ---
    @@ -0,0 +1,148 @@
    +---
    +title: Graph Generators
    +nav-parent_id: graphs
    +nav-pos: 6
    +---
    +<!--
    +Licensed to the Apache Software Foundation (ASF) under one
    +or more contributor license agreements.  See the NOTICE file
    +distributed with this work for additional information
    +regarding copyright ownership.  The ASF licenses this file
    +to you under the Apache License, Version 2.0 (the
    +"License"); you may not use this file except in compliance
    +with the License.  You may obtain a copy of the License at
    +
    +  http://www.apache.org/licenses/LICENSE-2.0
    +
    +Unless required by applicable law or agreed to in writing,
    +software distributed under the License is distributed on an
    +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    +KIND, either express or implied.  See the License for the
    +specific language governing permissions and limitations
    +under the License.
    +-->
    +
    +* This will be replaced by the TOC
    +{:toc}
    +
    +Bipartite Graph
    +---------------
    +
    +A bipartite graph (also called a two-mode graph) is a type of graph where vertices are
separated into two disjoint sets. These sets are usually called top and bottom vertices. A
single edge in this graph can only connect vertices from opposite sets (i.e. bottom vertex
to top vertex) and cannot connect to vertices in the same set.
    +
    +Theses graphs have wide application in practice and can be a more natural choice for
particular domains. For example to represent authorship of scientific papers top vertices
can represent scientific papers while bottom nodes will represent authors. Naturally a node
between a top and a bottom nodes would represent an authorship of a particular scientific
paper. Another common example for applications of bipartite graphs is a relationships between
actors and movies. In this case an edge represents that a particular actor played in a movie.
    +
    +Bipartite graph are used instead of regular graphs (one-mode) for the following practical
[reasons](http://www.complexnetworks.fr/wp-content/uploads/2011/01/socnet07.pdf):
    + * They preserve more information about a connection between vertices. For example instead
of a single link between two researchers in a graph that represents that they authored a paper
together a bipartite graph preserve the information about what papers they authored
    + * Bipartite graph can encode the same information more compactly than one-mode graphs
    + 
    +
    +
    +Graph Representation
    +--------------------
    +
    +A `BipartiteGraph` is represented by:
    + * `DataSet` of top nodes
    + * `DataSet` of bottom nodes
    + * `DataSet` of edges between top and bottom nodes
    +
    +As in the `Graph` class nodes are represented by the `Vertex` type and the same rules
applies to its types and values.
    +
    +The graph edges are represented by the `BipartiteEdge` type. An `BipartiteEdge` is defined
by a top ID (the ID of the top `Vertex`), a bottom ID (the ID of the bottom `Vertex`) and
an optional value. The main difference between the `Edge` and `BipartiteEdge` is that IDs
of nodes it links can be of different types. Edges with no value have a `NullValue` value
type.
    +
    +<div class="codetabs" markdown="1">
    +<div data-lang="java" markdown="1">
    +{% highlight java %}
    +BipartiteEdge<Long, String, Double> e = new BipartiteEdge<Long, String, Double>(1L,
"id1", 0.5);
    +
    +Double weight = e.getValue(); // weight = 0.5
    +{% endhighlight %}
    +</div>
    +
    +<div data-lang="scala" markdown="1">
    +{% highlight scala %}
    +// TODO: Should be added when Scala interface is implemented
    --- End diff --
    
    Don't leave a TODO in the docs. Either state explicitly that BipartiteGraph currently
only exists in the Java API or we should make sure to implement the Scala methods before merging
this.


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