226 lines
5.9 KiB
Plaintext
226 lines
5.9 KiB
Plaintext
/*
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----
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This file is part of SECONDO.
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Copyright (C) 2012, University in Hagen
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Faculty of Mathematic and Computer Science,
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Database Systems for New Applications.
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SECONDO is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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SECONDO is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with SECONDO; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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----
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\tableofcontents
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\newpage
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1 Overview
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The following is a slightly modified example taken from [RWE15].
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\begin{figure}[h]
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\centerline{
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\includegraphics[width=0.7\textwidth]{graph.eps}}
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\end{figure}
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2 Prepare data
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2.1 Create database
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Create a SECONDO database named "pgraph1" and enter it.
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*/
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SECONDO> create database pgraph1;
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SECONDO> open database pgraph1;
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/*
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2.2 Create relations and insert data
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The script ~createrels~ will create all node and edge relations and insert
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the data to reflect the graph shown above.
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*/
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SECONDO> @../Algebras/PropertyGraph2/sample-pregel/sample-shakespeare/createrels
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/*
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This script uses operators from ~RelationAlgebra~ and ~UpdateRelation~.
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Edge relations names are in uppercase, node relations are using only
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the first character in uppercase. (This convention is used by the PropertyGraphAlgebra)
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2.2 Create Ordered-Relations
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With the Ordered Relations it is possbile
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to query a persistent and non-distributed graph. The Ordered-Realtions can
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be created by the following script:
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*/
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SECONDO> @../Algebras/PropertyGraph2/sample-pregel/sample-shakespeare/create_orel
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/*
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3 Creating a property graph
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A property graph has to be defined before matching operators can be
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used to query the graph. This is done be registering the node and edge
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relations. (This defines the schema of the graph)
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*/
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SECONDO> @../Algebras/PropertyGraph2/sample-pregel/sample-shakespeare/create
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/*
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At first a PropertyGraph object is created. The argument "p1" is
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used to prefix objects in the memory catalog to keep the data
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of multiple graphs separated.
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*/
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let p1=createpgraph("p1");
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/*
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To define the schema of the graph, the script ~create~ uses the
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following operators to register the property graph:
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* ~createpgraph(name)~ to create a property graph object
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* ~addnodesrel[relname,fromclause,toclause]~ to register node relations
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* ~addedgesrel[relanme,propertyname, indexname]~ to register edge relations
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* ~addnodeindex[relanme]~ to register node property indexes
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This configuration will be saved in the database and will
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be available between sessions.
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To get information about the configuration of a property graph
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objects, use the ~info~ operator.
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*/
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SECONDO> query p1 info;
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/*
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4 Loading the graph
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To be able to query the property graph, it needs to be loaded with the operator
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loadgraphorel.
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This will create the statistics of the graph (at the first excecution) and
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additional structures to support the match operators.
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*/
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SECONDO> query p1 loadgraphorel;
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/*
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After loading the graph, the structure of the graph is set to "orel".
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5 Querying the property graph
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Now the prerequisites have been created to query the graph with persistent
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ordered relations.
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There are different matching operators available.
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All operators are returning a stream of tuples defined by the
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particular output field list.
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5.1 Querying by giving a full querytree (match1)
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The operator will find all subgraphs that are described
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by the querytree by having the same typed node and edge structure
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and passing all filter criteria. Nodes and edges having
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an alias (like theater) can be referenced to define the
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output field list and in the filter criteria list.
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The seach for subgraph matches is done along the query
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tree - so the query tree can be seen as query plan.
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This operator has the following arguments:
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1 The property graph object
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2 A stream of nodes that will be the starting positions for a subgraph match
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3 A query tree in list form. This tree describes a subtree that
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should be matched.
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4 Additional filter criteria
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5 Output field list
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This query is available in file ~match1~:
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*/
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SECONDO> @../Algebras/PropertyGraph/sample-shakespeare/match1
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/*
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5.2 Querying by giving a querytree (match2)
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This operator is not using a query tree anymore. It is given
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the subgraph pattern as a graph. The starting point - and so
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the query plan - will be choosen automatically by taking
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statistical data into account. The operator will open the
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corresponding edge list automatically - no node stream is necessary
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anymore.
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This operator has the following arguments:
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1 The property graph object
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2 The query graph in list form
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3 Additional filter criteria
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4 Output field list
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This query is available in file ~match2~:
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*/
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SECONDO> @../Algebras/PropertyGraph/sample-shakespeare/match2
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/*
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5.3 Using Cypher language for querying (match3)
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The readability of the previous expression as list is limited for
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complex queries. The graph query language cypher tries to improve that by
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having a syntax that is very intuitive and "whiteboard friendly".
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(See [CYP20] for more details)
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Nodes and edges are drawn like (x)--$>$(y) with some annotations.
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This operator has the following arguments:
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1 The property graph object
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2 The query coded as cypher expression
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This query is available in file ~match3~:
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*/
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SECONDO> @../Algebras/PropertyGraph/sample-shakespeare/match3
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/*
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6 References
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[RWE15] Ian Robinson, Jim Webber, and Emil Eifrem: \emph{Graph Databases}, O'Reilly Media, Inc., 2015.
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[CYP20] https://neo4j.com/docs/cypher-manual/current/
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*/
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