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---+ Replication Example: Star Topology

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---++Introduction
The following How-To walks you through setting up Virtuoso RDF Graph Replication in a Star Topology.
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---++Prerequisites
---+++Database INI Parameters

Suppose there are 3 Virtuoso instances respectively with the following ini parameters values:

   1. virtuoso1.ini:
<verbatim>
...
[Database]
DatabaseFile    = virtuoso1.db
TransactionFile = virtuoso1.trx
ErrorLogFile     = virtuoso1.log
...
[Parameters]
ServerPort               = 1111
SchedulerInterval        = 1
...
[HTTPServer]
ServerPort                  = 8891
...
[URIQA]
DefaultHost = localhost:8891
...
[Replication]
ServerName   = db1
...
</verbatim>
   1. virtuoso2.ini:
<verbatim>
...
[Database]
DatabaseFile    = virtuoso2.db
TransactionFile = virtuoso2.trx
ErrorLogFile     = virtuoso2.log
...
[Parameters]
ServerPort               = 1112
SchedulerInterval        = 1
...
[HTTPServer]
ServerPort                  = 8892
...
[URIQA]
DefaultHost = localhost:8892
...
[Replication]
ServerName   = db2
...
</verbatim>
   1. virtuoso3.ini:
<verbatim>
...
[Database]
DatabaseFile    = virtuoso3.db
TransactionFile = virtuoso3.trx
ErrorLogFile     = virtuoso3.log
...
[Parameters]
ServerPort               = 1113
SchedulerInterval        = 1
...
[HTTPServer]
ServerPort                  = 8893
...
[URIQA]
DefaultHost = localhost:8893
...
[Replication]
ServerName   = db3
...
</verbatim>
 

---+++Database DSNs

Use the ODBC Administrator on your Virtuoso host (e.g., on Windows, *Start* menu -> *Control Panel* -> *Administrative Tools* -> <b>Data Sources (ODBC)</b>; on Mac OS X, <code><nowiki>/Applications/Utilities/OpenLink ODBC Administrator.app</nowiki></code>) to create a System DSN for each of db1, db2, db3, with names db1, db2 and db3, respectively.

---+++Install Conductor package

On each of the 3 Virtuoso instances install the [[https://virtuoso.openlinksw.com/download/][conductor_dav.vad]] package.


---++Create a Publication on the Host Virtuoso Instance -- db1

   1 Go to *Conductor* -> *Replication* -> *Transactional* -> *Publications*:
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   1 Click <b>Enable RDF Publishing</b>.
   1 A publication with the name *RDF Publication* should be created:
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   1 Click the link which is the publication name.
   1 You will be shown the publication items page:
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   1 Enter for <b>Graph IRI</b>
<verbatim>
http://example.org
</verbatim>
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   1 Click <b>Add New</b>.
   1 The item will be created and shown in the list of items for the currently viewed publication.
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---++Insert Data into a Named Graph on the Host Virtuoso Instance

There are several ways to insert data into a Virtuoso Named Graph. In this Guide, we will use the Virtuoso Conductor's <b>Import RDF</b> feature:

   1. In the Virtuoso Conductor, go to *Linked Data* -> *Quad Store Upload*:
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   1 In the presented form:
      * Tick the box for *Resource URL* and enter your resource URL, for e.g.:
<verbatim>
http://www.openlinksw.com/dataspace/person/kidehen@openlinksw.com#this
</verbatim>
      * Enter for *Named Graph IRI*:
<verbatim>
http://example.org
</verbatim>
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   1 Click <b>Upload</b>
   1 A successful upload will result in this message:
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   1 Check the inserted triples by executing a query like the following against the SPARQL endpoint, <code><nowiki>http://cname:port/sparql</nowiki></code> --
<verbatim>
SELECT * 
  FROM <http://example.org>
 WHERE { ?s ?p ?o }
</verbatim>
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   1 See how many triples have been inserted in your graph:
<verbatim>
SELECT COUNT(*) 
  FROM <http://example.org>
 WHERE { ?s ?p ?o }
</verbatim>
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---++Subscribe to the Publication on the a Destination Virtuoso Instance -- db2, db3, etc.

   1 Go to *Conductor* -> *Replication* -> *Transactional* -> *Subscriptions*:
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   1 Click <b>New Subscription</b>:
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   1 Specify a new Data Source Enter or selected target data source from the available connected Data Sources:
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   1 Click <b>Publications list</b>:
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   1 Select the <b>RDF Publication</b> and click <b>List Items</b>:
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   1 Click <b>Subscribe</b>.
   1 The subscription will be created:
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   1 Click <b>Sync</b>.
   1 Check the retrieved triples by executing the following query:
<verbatim>
SELECT * 
  FROM <http://example.org>
 WHERE {?s ?p ?o}
</verbatim>
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   1 See how many triples have been inserted into your graph by executing the following query:
<verbatim>
SELECT COUNT(*) 
  FROM <http://example.org>
 WHERE {?s ?p ?o}
</verbatim>
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These steps may be repeated for any number of Subscribers.


---++Insert Triples into the Host Virtuoso Instance Graph and check availability at Destination Virtuoso Instance Graph

   1. To check the starting count, on the Destination Virtuoso Instance SPARQL Endpoint, execute:
<verbatim>
SELECT COUNT(*) 
  FROM <http://example.org>
 WHERE { ?s ?p ?o }
</verbatim>
   1. On the Host Virtuoso Instance go to *Conductor* -> *Database* -> *Interactive SQL* and execute the following statement:
<verbatim>
SPARQL INSERT INTO GRAPH <http://example.org> 
  { 
     <http://www.openlinksw.com/dataspace/person/kidehen@openlinksw.com#this>
     <http://xmlns.com/foaf/0.1/interest>
     <http://dbpedia.org/resource/Web_Services> 
  } ;
SPARQL INSERT INTO GRAPH <http://example.org> 
  { 
    <http://www.openlinksw.com/dataspace/person/kidehen@openlinksw.com#this>  	
    <http://xmlns.com/foaf/0.1/interest>  	
    <http://dbpedia.org/resource/Web_Clients> 
  } ;
SPARQL INSERT INTO GRAPH <http://example.org> 
  { 
    <http://www.openlinksw.com/dataspace/person/kidehen@openlinksw.com#this>  	
    <http://xmlns.com/foaf/0.1/interest>  	
    <http://dbpedia.org/resource/SPARQL> 
  } ;
</verbatim>
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   1. To confirm that the triple count has increased by the number of inserted triples, execute the following on the Destination Virtuoso Instance SPARQL Endpoint:
<verbatim>
SELECT COUNT(*) 
  FROM <http://example.org>
 WHERE { ?s ?p ?o }
</verbatim>
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---++Related

   * [[VirtGraphReplicationChain][Replication Example: Chain Topology]]
   * [[VirtGraphReplicationBiDirectional][Replication Example: 2-node Bi-directional Topology]]   
   * [[VirtGraphReplicationPSQL][Set up RDF Replication via procedure calls]]   
   * [[http://ods.openlinksw.com/wiki/ODS/VirtPubSubHub][Example of Linked Data Usage of PubSubHubbub Implementation]]
   * [[VirtRdfReplScenarios][Exploit Virtuoso's Replication Functionality Web based Solutions]]