Github user njayaram2 commented on a diff in the pull request:
https://github.com/apache/incubator-madlib/pull/141#discussion_r125086122
--- Diff: src/ports/postgres/modules/graph/bfs.sql_in ---
@@ -0,0 +1,435 @@
+/* -----------------------------------------------------------------------
*//**
+ *
+ * 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.
+ *
+ *
+ * @file bfs.sql_in
+ *
+ * @brief SQL functions for graph analytics
+ * @date Nov 2016
+ *
+ * @sa Provides Breadth First Search graph algorithm.
+ *
+ *//*
----------------------------------------------------------------------- */
+m4_include(`SQLCommon.m4')
+/**
+@addtogroup grp_bfs
+
+<div class="toc"><b>Contents</b>
+<ul>
+<li><a href="#bfs">Breadth-first Search</a></li>
+<li><a href="#notes">Notes</a></li>
+<li><a href="#examples">Examples</a></li>
+<li><a href="#literature">Literature</a></li>
+</ul>
+</div>
+
+@brief Finds the nodes reachable from a given source vertex using a
breadth-first approach.
+
+Given a graph and a source vertex, the Breadth-first Search (BFS) algorithm
+finds all nodes reachable from the source vertex by searching / traversing
the graph
+in a breadth-first manner.
+
+@anchor bfs
+@par BFS
+<pre class="syntax">
+graph_bfs( vertex_table,
+ vertex_id,
+ edge_table,
+ edge_args,
+ source_vertex,
+ out_table,
+ max_distance,
+ directed,
+ grouping_cols
+ )
+</pre>
+
+\b Arguments
+<dl class="arglist">
+<dt>vertex_table</dt>
+<dd>TEXT. Name of the table containing the vertex data for the graph. Must
contain the
+column specified in the 'vertex_id' parameter below.</dd>
+
+<dt>vertex_id</dt>
+<dd>TEXT, default = 'id'. Name of the column in 'vertex_table' containing
+vertex ids. The vertex ids are of type INTEGER with no duplicates.
+They do not need to be contiguous.</dd>
+
+<dt>edge_table</dt>
+<dd>TEXT. Name of the table containing the edge data. The edge table must
+contain columns for source vertex, destination vertex and edge weight.
+Column naming convention is described below in the 'edge_args'
parameter.</dd>
+
+<dt>edge_args</dt>
+<dd>TEXT. A comma-delimited string containing multiple named arguments of
+the form "name=value". The following parameters are supported for
+this string argument:
+ - src (INTEGER): Name of the column containing the source vertex ids in
the edge table.
+ Default column name is 'src'.
+ (Not to be confused with the source_vertex argument passed to the BFS
function)
+ - dest (INTEGER): Name of the column containing the destination vertex
ids in
+ the edge table. Default column name is 'dest'.
+
+<dt>source_vertex</dt>
+<dd>INTEGER. The source vertex id for the algorithm to start. This vertex
id must
+exist in the 'vertex_id' column of 'vertex_table'.</dd>
+
+<dt>out_table</dt>
+<dd>TEXT. Name of the table to store the result of BFS.
+It contains a row for every vertex that is reachable from the
source_vertex.
+In the presence of grouping columns, only those edges are used for which
there are no NULL values
+in any grouping column.
+The output table will have the following columns (in addition to the
grouping columns):
+ - vertex_id : The id for any node reachable from source_vertex.
+ Will use the input parameter 'vertex_id' for column naming.
+ - dist : The number of edges (or hops) from the source_vertex to
where this vertex is located.
+ - parent : The parent of this vertex in BFS traversal of the graph
from source_vertex.
+ Will use 'parent' for column naming. For the
+ case where vertex_id = source_vertex, the value for parent
is NULL.
+
+A summary table named <out_table>_summary is also created. This is an
internal table that keeps a record of the input parameters.
+</dd>
+
+<dt>max_distance</dt>
+<dd>INT, default = NULL. Maximum distance (number of edges) from
source_vertex to search through in the graph.</dd>
+
+<dt>directed</dt>
+<dd>BOOLEAN, default = FALSE. If TRUE the graph will be treated as
directed, else it will be treated as an undirected graph.</dd>
+
+<dt>grouping_cols</dt>
+<dd>TEXT, default = NULL. List of columns used to group the input into
discrete subgraphs. These columns must exist in the edge table. When this value
is NULL, no grouping is used and a single BFS result is generated. </dd>
+</dl>
--- End diff --
Does this implementation support expressions for grouping_cols? If not, we
should make a note here stating we don't support expressions for grouping
columns (please check pagerank/sssp docs for reference).
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