pgr_binaryBreadthFirstSearch - Experimental¶

pgr_binaryBreadthFirstSearch — Returns the shortest path(s) in a binary graph. Any graph whose edge-weights belongs to the set {0,X}, where ‘X’ is any non-negative real integer, is termed as a ‘binary graph’.

Boost Graph Inside

Warning

Possible server crash

These functions might create a server crash

Warning

Experimental functions

They are not officially of the current release.
They likely will not be officially be part of the next release:
- The functions might not make use of ANY-INTEGER and ANY-NUMERICAL
- Name might change.
- Signature might change.
- Functionality might change.
- pgTap tests might be missing.
- Might need c/c++ coding.
- May lack documentation.
- Documentation if any might need to be rewritten.
- Documentation examples might need to be automatically generated.
- Might need a lot of feedback from the comunity.
- Might depend on a proposed function of pgRouting
- Might depend on a deprecated function of pgRouting

Availability

To-be experimental on v3.0.0

Description¶

It is well-known that the shortest paths between a single source and all other vertices can be found using Breadth First Search in \(O(|E|)\) in an unweighted graph, i.e. the distance is the minimal number of edges that you need to traverse from the source to another vertex. We can interpret such a graph also as a weighted graph, where every edge has the weight 1. If not all edges in graph have the same weight, that we need a more general algorithm, like Dijkstra’s Algorithm which runs in \(O(|E|log|V|)\) time.

However if the weights are more constrained, we can use a faster algorithm. This algorithm, termed as ‘Binary Breadth First Search’ as well as ‘0-1 BFS’, is a variation of the standard Breadth First Search problem to solve the SSSP (single-source shortest path) problem in \(O(|E|)\), if the weights of each edge belongs to the set {0,X}, where ‘X’ is any non-negative real integer.

The main Characteristics are:

Process is done only on ‘binary graphs’. (‘Binary Graph’: Any graph whose edge-weights belongs to the set {0,X}, where ‘X’ is any non-negative real integer.)

For optimization purposes, any duplicated value in the start_vids or end_vids are ignored.

The returned values are ordered:

start_vid ascending

end_vid ascending

Running time: \(O(| start\_vids | * |E|)\)

Signatures¶

pgr_binaryBreadthFirstSearch(edges_sql, start_vid,  end_vid  [, directed])
pgr_binaryBreadthFirstSearch(edges_sql, start_vid,  end_vids [, directed])
pgr_binaryBreadthFirstSearch(edges_sql, start_vids, end_vid  [, directed])
pgr_binaryBreadthFirstSearch(edges_sql, start_vids, end_vids [, directed])
RETURNS SET OF (seq, path_seq [, start_vid] [, end_vid], node, edge, cost, agg_cost)
OR EMPTY SET

pgr_binaryBreadthFirstSearch(TEXT edges_sql, BIGINT start_vid, BIGINT end_vid)
RETURNS SET OF (seq, path_seq, node, edge, cost, agg_cost) or EMPTY SET

Example:	From vertex \(2\) to vertex \(3\) on a directed binary graph

SELECT * FROM pgr_binaryBreadthFirstSearch(
    'SELECT id, source, target, road_work as cost, reverse_road_work as reverse_cost FROM roadworks',
    2, 3
);
 seq | path_seq | node | edge | cost | agg_cost
-----+----------+------+------+------+----------
   1 |        1 |    2 |    4 |    0 |        0
   2 |        2 |    5 |    8 |    1 |        0
   3 |        3 |    6 |    9 |    1 |        1
   4 |        4 |    9 |   16 |    0 |        2
   5 |        5 |    4 |    3 |    0 |        2
   6 |        6 |    3 |   -1 |    0 |        2
(6 rows)

One to One¶

pgr_binaryBreadthFirstSearch(TEXT edges_sql, BIGINT start_vid, BIGINT end_vid,
BOOLEAN directed:=true);
RETURNS SET OF (seq, path_seq, node, edge, cost, agg_cost)
OR EMPTY SET

Example:	From vertex \(2\) to vertex \(3\) on an undirected binary graph

SELECT * FROM pgr_binaryBreadthFirstSearch(
    'SELECT id, source, target, road_work as cost, reverse_road_work as reverse_cost FROM roadworks',
    2, 3,
    FALSE
);
 seq | path_seq | node | edge | cost | agg_cost
-----+----------+------+------+------+----------
   1 |        1 |    2 |    2 |    1 |        0
   2 |        2 |    3 |   -1 |    0 |        1
(2 rows)

One to many¶

pgr_binaryBreadthFirstSearch(TEXT edges_sql, BIGINT start_vid, ARRAY[ANY_INTEGER] end_vids,
BOOLEAN directed:=true);
RETURNS SET OF (seq, path_seq, end_vid, node, edge, cost, agg_cost)
OR EMPTY SET

Example:	From vertex \(2\) to vertices \(\{3, 5\}\) on an undirected binary graph

SELECT * FROM pgr_binaryBreadthFirstSearch(
    'SELECT id, source, target, road_work as cost FROM roadworks',
    2, ARRAY[3,5],
    FALSE
);
 seq | path_seq | end_vid | node | edge | cost | agg_cost
-----+----------+---------+------+------+------+----------
   1 |        1 |       3 |    2 |    4 |    0 |        0
   2 |        2 |       3 |    5 |    8 |    1 |        0
   3 |        3 |       3 |    6 |    5 |    1 |        1
   4 |        4 |       3 |    3 |   -1 |    0 |        2
   5 |        1 |       5 |    2 |    4 |    0 |        0
   6 |        2 |       5 |    5 |   -1 |    0 |        0
(6 rows)

Many to One¶

pgr_binaryBreadthFirstSearch(TEXT edges_sql, ARRAY[ANY_INTEGER] start_vids, BIGINT end_vid,
    BOOLEAN directed:=true);
RETURNS SET OF (seq, path_seq, start_vid, node, edge, cost, agg_cost)
OR EMPTY SET

Example:	From vertices \(\{2, 11\}\) to vertex \(5\) on a directed binary graph

SELECT * FROM pgr_binaryBreadthFirstSearch(
    'SELECT id, source, target, road_work as cost, reverse_road_work as reverse_cost FROM roadworks',
    ARRAY[2,11], 5
);
 seq | path_seq | start_vid | node | edge | cost | agg_cost
-----+----------+-----------+------+------+------+----------
   1 |        1 |         2 |    2 |    4 |    0 |        0
   2 |        2 |         2 |    5 |   -1 |    0 |        0
   3 |        1 |        11 |   11 |   13 |    1 |        0
   4 |        2 |        11 |   12 |   15 |    0 |        1
   5 |        3 |        11 |    9 |   16 |    0 |        1
   6 |        4 |        11 |    4 |    3 |    0 |        1
   7 |        5 |        11 |    3 |    2 |    1 |        1
   8 |        6 |        11 |    2 |    4 |    0 |        2
   9 |        7 |        11 |    5 |   -1 |    0 |        2
(9 rows)

Many to Many¶

pgr_binaryBreadthFirstSearch(TEXT edges_sql, ARRAY[ANY_INTEGER] start_vids, ARRAY[ANY_INTEGER] end_vids,
    BOOLEAN directed:=true);
RETURNS SET OF (seq, path_seq, start_vid, end_vid, node, edge, cost, agg_cost)
OR EMPTY SET

Example:	From vertices \(\{2, 11\}\) to vertices \(\{3, 5\}\) on an undirected binary graph

SELECT * FROM pgr_binaryBreadthFirstSearch(
    'SELECT id, source, target, road_work as cost, reverse_road_work as reverse_cost FROM roadworks',
    ARRAY[2,11], ARRAY[3,5],
    FALSE
);
 seq | path_seq | start_vid | end_vid | node | edge | cost | agg_cost
-----+----------+-----------+---------+------+------+------+----------
   1 |        1 |         2 |       3 |    2 |    2 |    1 |        0
   2 |        2 |         2 |       3 |    3 |   -1 |    0 |        1
   3 |        1 |         2 |       5 |    2 |    4 |    0 |        0
   4 |        2 |         2 |       5 |    5 |   -1 |    0 |        0
   5 |        1 |        11 |       3 |   11 |   13 |    1 |        0
   6 |        2 |        11 |       3 |   12 |   15 |    0 |        1
   7 |        3 |        11 |       3 |    9 |   16 |    0 |        1
   8 |        4 |        11 |       3 |    4 |    3 |    0 |        1
   9 |        5 |        11 |       3 |    3 |   -1 |    0 |        1
  10 |        1 |        11 |       5 |   11 |   12 |    0 |        0
  11 |        2 |        11 |       5 |   10 |   10 |    1 |        0
  12 |        3 |        11 |       5 |    5 |   -1 |    0 |        1
(12 rows)

Parameters¶

Parameter	Type	Default	Description
edges_sql	`TEXT`		Inner SQL query as described below.
start_vid	`BIGINT`		Identifier of the starting vertex of the path.
start_vids	`ARRAY[BIGINT]`		Array of identifiers of starting vertices.
end_vid	`BIGINT`		Identifier of the ending vertex of the path.
end_vids	`ARRAY[BIGINT]`		Array of identifiers of ending vertices.
directed	`BOOLEAN`	`true`	When `true` Graph is considered Directed When `false` the graph is considered as Undirected.

Inner query¶

Column	Type	Default	Description
id	`ANY-INTEGER`		Identifier of the edge.
source	`ANY-INTEGER`		Identifier of the first end point vertex of the edge.
target	`ANY-INTEGER`		Identifier of the second end point vertex of the edge.
cost	`ANY-NUMERICAL`		Weight of the edge (source, target) When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost	`ANY-NUMERICAL`	-1	Weight of the edge (target, source), When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER:	SMALLINT, INTEGER, BIGINT
ANY-NUMERICAL:	SMALLINT, INTEGER, BIGINT, REAL, FLOAT

Return Columns¶

Returns set of (seq, path_id, path_seq [, start_vid] [, end_vid], node, edge, cost, agg_cost)

Column	Type	Description
seq	`INT`	Sequential value starting from 1.
path_id	`INT`	Path identifier. Has value 1 for the first of a path. Used when there are multiple paths for the same `start_vid` to `end_vid` combination.
path_seq	`INT`	Relative position in the path. Has value 1 for the beginning of a path.
start_vid	`BIGINT`	Identifier of the starting vertex. Returned when multiple starting vetrices are in the query. Many to One Many to Many
end_vid	`BIGINT`	Identifier of the ending vertex. Returned when multiple ending vertices are in the query. One to Many Many to Many
node	`BIGINT`	Identifier of the node in the path from `start_vid` to `end_vid`.
edge	`BIGINT`	Identifier of the edge used to go from `node` to the next node in the path sequence. `-1` for the last node of the path.
cost	`FLOAT`	Cost to traverse from `node` using `edge` to the next node in the path sequence.
agg_cost	`FLOAT`	Aggregate cost from `start_v` to `node`.

Example Data¶

This type of data is used on the examples of this page.

Edwards-Moore Algorithm is best applied when trying to answer queries such as the following: “Find the path with the minimum number from Source to Destination” Here: * Source = Source Vertex, Destination = Any arbitrary destination vertex * X is an event/property * Each edge in the graph is either “X” or “Not X” .

Example: “Find the path with the minimum number of road works from Source to Destination”

Here, a road under work(aka road works) means that part of the road is occupied for construction work/maintenance.

Here: * Edge ( u , v ) has weight = 0 if no road work is ongoing on the road from u to v. * Edge ( u, v) has weight = 1 if road work is ongoing on the road from u to v.

Then, upon running the algorithm, we obtain the path with the minimum number of road works from the given source and destination.

Thus, the queries used in the previous section can be interpreted in this manner.

Table Data¶

The queries in the previous sections use the table ‘roadworks’. The data of the table:

DROP TABLE IF EXISTS roadworks CASCADE;
NOTICE:  table "roadworks" does not exist, skipping
DROP TABLE
CREATE table roadworks (
    id BIGINT not null primary key,
    source BIGINT,
    target BIGINT,
    road_work FLOAT,
    reverse_road_work FLOAT
);
CREATE TABLE
INSERT INTO roadworks(
  id, source, target, road_work, reverse_road_work) VALUES
  (1,  1,  2,  0,  0),
  (2,  2,  3,  -1,  1),
  (3,  3,  4,  -1,  0),
  (4,  2,  5,  0,  0),
  (5,  3,  6,  1,  -1),
  (6,  7,  8,  1,  1),
  (7,  8,  5,  0,  0),
  (8,  5,  6,  1,  1),
  (9,  6,  9,  1,  1),
  (10,  5,  10,  1,  1),
  (11,  6,  11,  1,  -1),
  (12,  10,  11,  0,  -1),
  (13,  11,  12,  1,  -1),
  (14,  10,  13,  1,  1),
  (15,  9,  12,  0,  0),
  (16,  4,  9,  0,  0),
  (17,  14,  15,  0,  0),
  (18,  16,  17,  0,  0);
INSERT 0 18

pgr_binaryBreadthFirstSearch - Experimental¶

Description¶

Signatures¶

One to One¶

One to many¶

Many to One¶

Many to Many¶

Parameters¶

Inner query¶

Return Columns¶

Example Data¶

Table Data¶

See Also¶