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Strabon

Introduction

Strabon is a fully implemented semantic geospatial database system that can be used to store linked geospatial data expressed in RDF and query them using an extension of SPARQL. Strabon supports spatial selections, spatial joins, a rich set of spatial functions similar to those offered by geospatial relational database systems, support for multiple Coordinate Reference Systems and widely used serializations for geometric objects such as WKT and GML. Strabon is built on top of the well-known RDF store Sesame and extends Sesame’s components to be able to manage thematic and spatial data that are stored in PostGIS.

The development of Strabon started in the context of European FP7 project SemsorGrid4Env (Semantic Sensor Grids for Rapid Application Development for Environmental Management) [http://www.semsorgrid4env.eu/]. Starting September 2011, Strabon is being utilized and extended with new functionalities in the FP7 project TELEIOS (Virtual Observatory Infrastructure for Earth Observation Data) [http://www.earthobservatory.eu/] which our group leads.

The query language of Strabon is called stSPARQL. stSPARQL can be used to query data represented in an extension of RDF called stRDF. stRDF and stSPARQL have been designed for representing and querying geospatial data that changes over time (e.g., the growth of a city over the years due to new developments).

Currently, only the geospatial features of stSPARQL have been implemented fully. The temporal features are the subject of current work.

Given the very close relationship between stSPARQL and GeoSPARQL which is a recent OGC standard for an extension of SPARQL for querying geospatial metadata, we recently provided support for the Core, Geometry and Geometry Topology extension of GeoSPARQL.

Conformance to GeoSPARQL

Strabon implements the Core', the Topology Vocabulary Extension', the Geometry Extension', the Geometry Topology Extension', and the `RDFS Entailment Extension' except for Req. 25 (http://www.opengis.net/spec/geosparql/1.0/req/rdfs-entailment-extension/bgp-rdfs-ent).

With respect to GML, Strabon supports the GML Profile corresponding to Simple Features, that is, GML Simple Features Profile 2.0.

Strabon Homepage

The homepage of Strabon is at http://www.strabon.di.uoa.gr/.

Demo

You can find a demo of the system Strabon at http://test.strabon.di.uoa.gr/NOA/.

How to build and run Strabon from command line

Assuming you have already downloaded Strabon and you are in the top-level directory of Strabon, issue the following command to build it from command line:

$ mvn clean package

In order to run automatically the JUnit tests, pass the option `-DskipTests=false' to the above command. The complete command is the following:

$ mvn -DskipTests=false clean package

Alternatively, it is possible to run a specific test. Supposing that the name of the corresponding class is `TestName', then you can run only this test using the following command:

$ mvn test -DfailIfNoTests=false -DskipTests=false -Dtest=TestName

In case of an error during building of Strabon and assuming that the error does not come from the JUnit tests, please have a look at the Known Issues' section below. If none of the known issues of that section applies, please contact the developers through the Strabon mailing-list or submit a corresponding bug (see Bugs' section below).

After you have successfully built Strabon, you have access to the following components:

  • Strabon Endpoint

    This is a SPARQL endpoint for Strabon. It is distributed as a war file so you may deploy it in a Tomcat container. You may find the war file under directory `endpoint/target'.

  • Strabon Endpoint (standalone)

    This is a SPARQL endpoint for Strabon like the above one, but it differs only in that it does not require the user to have already set up a Tomcat container. The standalone Strabon Endpoint may be run by issuing the following command:

    $ java -jar endpoint-exec/target/strabon-endpoint-executable-${version}.jar

    After issuing the above command, you may access the Strabon Endpoint at the following URL: http://localhost:8080/.

    Please see the page at http://hg.strabon.di.uoa.gr/Strabon/rev/674f8f91162b to find out other options that you may pass to the Tomcat container that will run by the above command.

    SPECIAL NOTE: if you need to configure the connection details to the underlying database, you may do so in two ways:

    1. By modifying file `endpoint/WebContent/WEB-INF/connection.properties' before building Strabon and executing the above command.
    2. After executing the above command, by visiting the following page by a browser: http://localhost:8080/ChangeConnection

  • Strabon Endpoint Client

    This is a Java client for interacting with Strabon Endpoint or any other SPARQL endpoint. It is packaged as a jar file and may be found under directory endpoint-client/target/' with name strabon-endpoint-client-${version}.jar'. This jar contains any dependencies to other code, so may copy and paste it to your project and start playing with the code immediately.

  • Strabon script

    The strabon' script is located under the scripts/' directory and it is the main command-line tool for interacting with Strabon. You may use it to store RDF data with geospatial information or query/update it using one of stSPARQL or GeoSPARQL query languages.

  • Endpoint script

    The endpoint' script is located under the scripts' directory and it is the main command-line tool for interacting with a Strabon Endpoint'. You may use it to do any operation you would like to do with the strabon' script above, but in contrast to the strabon' script you need to have access to a Strabon endpoint. Of course, the Strabon Endpoint Client' component above can be used as well as a command-line tool. At the time of writing, the `Strabon Endpoint Client' component supports only querying of RDF data with geospatial information.

Getting Started

To get started with Strabon please have a look at the tutorial for the stRDF data model and stSPARQL query language, the User Guide, and the Developer Guide.

stRDF and stSPARQL tutorial http://www.strabon.di.uoa.gr/files/stSPARQL_tutorial.pdf

stSPARQL Reference

The reference for the spatial and temporal extension functions defined in stSPARQL can be found at http://www.strabon.di.uoa.gr/stSPARQL#spatial and http://www.strabon.di.uoa.gr/stSPARQL#temporals respectively.

User Guide

Assuming that you are familiar with Maven, the following steps need to be followed in order to use Strabon using Eclipse:

  1. Install PostgreSQL from http://www.postgresql.org/download/. At the time of this writing the latest PostgreSQL version is 9.1.
  2. Install PostGIS from http://postgis.refractions.net/download/. At the time of this writing we have tested Strabon with PostGIS 1.5.3.
  3. Install Maven from http://maven.apache.org/download.html. At the time of this writing the latest Maven version is 3.0.4.
  4. Install Eclipse from http://www.eclipse.org/downloads/. At the time of this writing the latest Eclipse version is 3.7.2.
  5. Install the m2e plugin for Eclipse from http://www.eclipse.org/m2e/.
  6. Install the MercurialEclipse plugin for Eclipse from http://javaforge.com/project/HGE .
  7. From Eclipse, go to File --> Import --> Mercurial --> Clone Existing Mercurial Repository --> Next. In the URL textarea paste the following URL: http://hg.strabon.di.uoa.gr/StrabonUser and then press Next --> Next --> Finish. If you used the default settings, you should have a new project named StrabonMain. Right click on the project and select Configure --> Convert to Maven project. Eclipse will enable Maven dependency management for the project, download any dependencies and build the project.

Storing stRDF graphs and evaluating stSPARQL queries

You can see some examples in the classes gr.uoa.di.strabon.example.PostgisExample and gr.uoa.di.strabon.example.PostgisExample2.

Tuning PostgreSQL

The default settings of Postgres are rather conservative. As a result, parameter tuning is neccessary for speeding up Postgres, therefore Strabon. If you are using Strabon to compare its performance against your implementation of stSPARQL/GeoSPARQL, you are strongly encouraged to contact us using the Strabon Users mailing list for assistance on tuning Postgres.

You can follow the instructions below for tuning a Postgres server running on an Ubuntu machine that is dedicated to PostgreSQL and Strabon.

  1. Append the following text at the end of postgresql.conf. Uncomment the appropriate lines.
### RAM
## 4 GB of RAM
#shared_buffers       =  3GB
#effective_cache_size =  3GB
#maintenance_work_mem =  1GB
#work_mem             =  2GB
## 8 GB of RAM
#shared_buffers       =  5GB
#effective_cache_size =  6GB
#maintenance_work_mem =  2GB
#work_mem             =  5GB
## 16 GB of RAM
#shared_buffers       = 10GB
#effective_cache_size = 14GB
#maintenance_work_mem =  4GB
#work_mem             = 10GB
## 24 GB of RAM
#shared_buffers       = 16GB
#effective_cache_size = 22GB
#maintenance_work_mem =  6GB
#work_mem             = 15GB
## 48 GB of RAM
#shared_buffers       = 32GB
#effective_cache_size = 46GB
#maintenance_work_mem =  8GB
#work_mem             = 30GB
## 64 GB of RAM
# contact us to find out!
### HD
## RAID with ordinary 7.200 disks
#random_page_cost = 3.5 #3.0-3.5
## High-End NAS/SAN
#random_page_cost = 2 #1.5-2.5
## Amazon EBS/Heroku
#random_page_cost = 1.3 #1.1-2.0
## SSD array
#random_page_cost = 2.0 #1.5-2.5
### Planner options
# Increase the following values in order to avoid using the GEQO planner.
# Small values (<8) reduce planning time but may produce inferior query plans
#
geqo_threshold = 15 # keep this value larger that the following two parameters
from_collapse_limit = 14
join_collapse_limit = 14
### Misc
default_statistics_target    = 10000 
constraint_exclusion         = on 
checkpoint_completion_target = 0.9 
wal_buffers                  = 32MB 
checkpoint_segments          = 64 
### Connections
max_connections              = 10
  1. Append the following lines at the end of /etc/sysctl.conf Uncomment the appropriate lines.
## 4 GB of RAM
#kernel.shmmax = 3758096384
#kernel.shmall = 3758096384
#kernel.shmmni = 4096
## 8 GB of RAM
#kernel.shmmax = 5905580032
#kernel.shmall = 5905580032
#kernel.shmmni = 4096
## 16 GB of RAM
#kernel.shmmax = 11274289152
#kernel.shmall = 11274289152
#kernel.shmmni = 4096
## 24 GB of RAM
#kernel.shmmax = 17716740096
#kernel.shmall = 17716740096
#kernel.shmmni = 4096
## 48 GB of RAM
#kernel.shmmax = 35433480192
#kernel.shmall = 35433480192
#kernel.shmmni = 4224
## 64 GB of RAM
# contact us to find out!
  1. Apply all changes by executing

$ sudo sysctl -p $ sudo /etc/init.d/postgresql restart

  1. Prepare for the next run by issuing the command

$ sudo -u postgres psql -c 'VACUUM ANALYZE;' db

or

$ psql -c 'VACUUM ANALYZE;' db

where db is the name of the Postgres database that Strabon will use.

Developer Guide

Assuming that you are familiar with Maven, the following steps need to be followed in order to use Strabon using Eclipse:

  1. Install PostgreSQL from http://www.postgresql.org/download/. At the time of this writing the latest PostgreSQL version is 9.1.
  2. Install PostGIS from http://postgis.refractions.net/download/. At the time of this writing we have tested Strabon with PostGIS 1.5.3.
  3. Install Maven from http://maven.apache.org/download.html. At the time of this writing the latest Maven version is 3.0.4.
  4. Install Eclipse from http://www.eclipse.org/downloads/. At the time of this writing the latest Eclipse version is 3.7.2.
  5. Install the m2e plugin for Eclipse from http://www.eclipse.org/m2e/.
  6. Install the MercurialEclipse plugin for Eclipse from http://javaforge.com/project/HGE.
  7. From Eclipse, go to File --> Import --> Mercurial --> Clone Existing Mercurial Repository --> Next. In the URL textarea paste the following URL: http://hg.strabon.di.uoa.gr/Strabon and then press Next --> Next --> Finish. If you used the default settings, you should have a new project named StrabonMain. Right click on the project and select Configure --> Convert to Maven project. Eclipse will enable Maven dependency management for the project, download any dependencies and build the project.

Tester Guide

Assuming again that you are familiar with Maven and Junit these are the steps you need to follow to test the functionality of Strabon:

  • Using Eclipse

    If you want to create a new test:

    1. Import Strabon into Eclipse as explained in the Developer Guide.
    2. Go to strabon-testsuite project.
    3. Create a new folder (Recommended folder name: <test's name>) and place inside the following files: 1. An ntriples or nquads file with the test dataset (with .nt or .nq extension). 2. Pairs of files with sparql test queries and expected test results in xml format. Notice that each pair must have the same name and .rq extension for the queryFile and .srx extension for the resultsFile.
    4. Create a test class that extends TemplateTest class.
    5. If you have followed the recommendations the test is ready. If you have different names or location for your files, insert them explicitly in the constructor of the class. WARNING: All prefixes must be placed in file "prefixes" so that every time a namespace changes, we have to change it just once.

    If you want to run a test:

    1. Right-click on the test class.
    2. Select "Run as JUnit Test".
    3. Database properties are retrieved from database.properties file. If you want, you can change a property "on the fly" with an environment variable.

  • Command Line

    If you want to run all the tests:

    1. Go to Strabon directory (root directory of all the subprojects).
    2. Run "mvn test -DskipTests=false".
    3. Optionally you can pass an environment variable with "-DvariableName=variableValue".

Storing stRDF graphs and evaluating stSPARQL queries

You can see some examples in the classes eu.earthobservatory.runtime.postgis.StoreOp and eu.earthobservatory.runtime.postgis.QueryOp.

Download

You can download the source code of the latest version of Strabon by accessing our public mercurial repository located at http://hg.strabon.di.uoa.gr/Strabon. You can find more information on how to use and extend Strabon at the Getting Started section.

Publications

You can learn about stRDF data model and stSPARQL query language employed in Strabon by reading our tutorial under the Getting Started section and/or the publications given on this page.

The current versions of stRDF and stSPARQL which are based on OGC standards are presented in the following document:

  • K. Kyzirakos, M. Karpathiotakis, and M. Koubarakis. Strabon: A Semantic Geospatial DBMS. In Internatioanl Semantic Web Conference (ISWC'12). Boston, USA, November 11-15, 2012. [pdf: http://strabon.di.uoa.gr/files/strabon-iswc.pdf]

  • Manolis Koubarakis, Kostis Kyzirakos, Babis Nikolaou, Michael Sioutis, and Stavros Vassos. A data model and query language for an extension of RDF with time and space. Deliverable D2.1, European ICT project TELEIOS, 2011. [pdf: http://strabon.di.uoa.gr/files/deliv2-1-re-revised.pdf]

The initial versions of stRDF and stSPARQL that are based on constraint databases are presented in the following publications:

  • Manolis Koubarakis and Kostis Kyzirakos. Modeling and Querying Metadata in the Semantic Sensor Web: the Model stRDF and the Query Language stSPARQL. In 7th Extended Semantic Web Conference (ESWC 2010). Heraklion, Crete, 30 May - 03 June, 2010. [pdf: http://strabon.di.uoa.gr/files/stSPARQL.pdf]

  • Kostis Kyzirakos, Manos Karpathiotakis and Manolis Koubarakis. Developing Registries for the Semantic Sensor Web using stRDF and stSPARQL (short paper). In Proceedings of 3rd International workshop on Semantic Sensor Networks 2010, in conjunction with ISWC 2010, November 2010, Shanghai, China. [pdf: http://strabon.di.uoa.gr/files/strabon.pdf]

Applications of stRDF, stSPARQL, and the system Strabon are described here:

  • Alasdair J. G. Gray, Raúl García-Castro, Kostis Kyzirakos, Manos Karpathiotakis, Jean-Paul Calbimonte, Kevin Page, Jason Sadler, Alex Frazer, Ixent Galpin, Alvaro A. A. Fernandes, Norman W. Paton, Oscar Corcho, Manolis Koubarakis, David De Roure, Kirk Martinez and Asunción Gómez-Pérez. A Semantically Enabled Service Architecture for Mashups over Streaming and Stored Data. In 8th Extended Semantic Web Conference (ESWC 2011). Heraklion, Crete, May 20 - June 2, 2011. [pdf: http://strabon.di.uoa.gr/files/Gray2011Architecture.pdf]

  • A.J.G. Gray, J. Sadler, O. Kit, K. Kyzirakos, M. Karpathiotakis, J.-P. Calbimonte, K. Page, R. García-Castro, A. Frazer, I. Galpin, A.A.A. Fernandes, N.W. Paton, O. Corcho, M. Koubarakis, D.D. Roure, K. Martinez, A. Gómez-Pérez. A Semantic Sensor Web for Environmental Decision Support Applications. Sensors. 11, 8855-8887. [pdf: http://strabon.di.uoa.gr/files/sensors-11-08855.pdf]

Coming up soon: Strabon will soon support an extension of RDF for incomplete geospatial information. The following publication gives a preview of the relevant research problems:

  • M. Koubarakis, K. Kyzirakos, M. Karpathiotakis, C. Nikolaou, M. Sioutis, S. Vassos, D. Michail, T. Herekakis, C. Kontoes and I. Papoutsis. Challenges for Qualitative Spatial Reasoning in Linked Geospatial Data. In Proceedings of IJCAI 2011 Workshop on Benchmarks and Applications of Spatial Reasoning, Barcelona, Spain. [pdf: http://www.earthobservatory.eu/publications/SciQL_ADASS2011.pdf]

  • C. Nikolaou and M. Koubarakis: "Querying Linked Geospatial Data with Incomplete Information". In 5th International Terra Cognita Workshop - Foundations, Technologies and Applications of the Geospatial Web. In conjunction with the 11th International Semantic Web Conference, Boston, USA, November, 2012. [http://www.earthobservatory.eu/publications/iswc-workshop.pdf]

Contributors

The system Strabon has been developed by the following members of our team:

Mailing-list

Currently, we maintain the following mailing lists:

Bugs

Please report bugs to http://bug.strabon.di.uoa.gr/report or the Strabon-devel mailing-list Strabon-devel@di.uoa.gr.

Known Issues

  • By default, Tomcat uses ISO-8859-1 character encoding when decoding URLs received from a browser. This can cause problems when encoding is UTF-8, and you are using international characters. In order to fix this, edit conf/server.xml and find the line where the Connector is defined. Add the parameter URIEncoding and set it to UTF-8. For example:

  • Building and executing any maven goals fails for maven versions <3.0 due to a dependency to the 'shade' plugin that is available only for maven version 3.0 (http://maven.apache.org/plugins/maven-shade-plugin/). In such systems, you may disable execution of this plugin by setting the environmental variable `shade.skip'. For example, to build Strabon using maven version 2.0 you may execute the following command:

    $ mvn clean package -Dshade.skip

  • When using MonetDB as a backend, the following source code of MonetDB must be used: https://hg.strabon.di.uoa.gr/MonetDB/

License

This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

Copyright (C) 2010, 2011, 2012, Pyravlos Team

http://www.strabon.di.uoa.gr/

How to apply the license

  • In the beginning of script files (after the shell directive) paste the following statement:
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
#
# Copyright (C) 2010, 2011, 2012, Pyravlos Team
#
# http://www.strabon.di.uoa.gr/
#
  • In the beginning of Java source code files paste the following statement:
/**
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright (C) 2010, 2011, 2012, Pyravlos Team
 *
 * http://www.strabon.di.uoa.gr/
 */
  • In the beginning of HTML/XML files paste the following statement:
<!-- This Source Code Form is subject to the terms of the Mozilla Public
   - License, v. 2.0. If a copy of the MPL was not distributed with this
   - file, You can obtain one at http://mozilla.org/MPL/2.0/.
   -
   - Copyright (C) 2010, 2011, 2012, Pyravlos Team
   -
   - http://www.strabon.di.uoa.gr/
-->

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