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Differential Revision: https://phabricator.memgraph.io/D783
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florijan 2017-09-13 13:38:53 +02:00
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46
docs/user_technical/open-cypher.md
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@ -395,6 +395,52 @@ index `label` and `property`. Do not create indices concurrently.
The following sections describe some of the other supported features.
#### Breadth First Search
A typical graph use-case is searching for the shortest path between nodes.
The openCypher standard does not define this feature. Neo4j offers the
`shortestPath` function-like invocation for this purpose.
Memgraph decided to offer the same functionality using the edge expansion syntax.
Finding the shortest path between nodes can be done using breadth-first
expansion:
MATCH (a {id: 723})-bfs[r:Type](e, n | true, 10)-(b {id : 882}) RETURN *
The above query will find all paths of length up to 10 between nodes `a` and `b`.
Just like in variable-length expansion, a single edge element in the query
pattern denotes a possibly longer path.
To find only the shortest path, simply append LIMIT 1 to the RETURN clause.
MATCH (a {id: 723})-bfs[r:Type](e, n | true, 10)-(b {id : 882}) RETURN * LIMIT 1
Breadth-fist expansion allows an arbitrary expression filter that determines
if an expansion is allowed. In the above query that expression is `true`, meaning
that all expansions are allowed. Following is an example in which expansion is
allowed only over edges whose `x` property is greater then `12` and nodes `y`
whose property is lesser then `3`:
MATCH (a {id: 723})-bfs[](e, n | e.x > 12 and n.y < 3, 10)-() RETURN *
Notice how the filtering expression uses `e` and `n` symbols. These symbols
don't have a fixed name, which is exactly why they have to be declared as the first
two arguments of the breadth-first expansion.
The edge symbol and edge types in the square brackets can be omitted, just like
in ordinary expansion. All other arguments (in the round brackets) are obligatory.
There are a few benefits of the breadth-first expansion approach, as compared to
the `shortestPath` function of Neo4j. For one, it is possible to inject
expressions that filter on nodes and edges along the path itself, not just the final
destination node. Furthermore, it's possible to find multiple paths to multiple destination
nodes regardless of their length. Also, it is possible to simply go through a node's
neighbourhood in breadth-first manner.
It is fair to say there are a few drawbacks too. Currently, it isn't possible to get
all shortest paths to a single node using Memgraph's breadth-first expansion. Also,
the syntax is a bit unwieldy.
#### UNWIND
The `UNWIND` clause is used to unwind a list of values as individual rows.

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docs/user_technical/upcoming-features.md
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@ -11,6 +11,7 @@ will be continually working on improving the performance. This includes:
* query compilation;
* query execution;
* core engine performance;
* algorithmic improvements (i.e. bidirectional breadth-first search);
* memory usage and
* other improvements.