Virtual Graph Configuration

This page describes virtual graph configuration in detail.

Page Contents

Overview
Virtual Graph Properties

Overview

As discussed in the How Virtual Graphs Work section, a virtual graph properties file is one of the three components that make up a Virtual Graph (the others being a unique name and mapping file). A virtual graph properties file must be in the Java properties file format.

We showed a minimal example (dept.properties) of a virtual graph properties file to connect to a MySQL database:

jdbc.url=jdbc:mysql://localhost/dept
jdbc.username=MySqlUserName
jdbc.password=MyPassword
jdbc.driver=com.mysql.jdbc.Driver

Recall, the name of the properties file without the extension (dept in the example used), will become the unique name of the virtual graph.

Below you’ll see all available virtual graph properties in addition to connection pool properties for the built-in Tomcat connection pool that can be modified. All of these properties should go inside the virtual graph properties file like the one shown above.

Virtual Graph Properties

The following tables list the available options for use in virtual graph properties files.

jdbc. properties are used for all relational data sources.

The following properties apply to all virtual graphs.

`base`

Default
Description	Base IRI used to resolve relative IRIs from virtual graphs.

`percent.encode`

Default	`true`
Description	Should IRI template strings be percent-encoded to be valid IRIs? (`true`/`false`)

`import.optimize`

Default	`true`
Description	Should `virtual import` and `?s ?p ?o` queries use the optimized translation? (`true`/`false`)

`parser.sql.quoting`

Default	`false`
Description	If unspecified, R2RML views (using `rr:sqlQuery`) will be parsed using the DB-native identifier quoting convention. For example, MySQL queries will be parsed treating backtick as the identifier quote character. If set to `ANSI`, the ANSI SQL convention of treating a double quote as the identifier quote character will be used instead.

`sql.functions`

Default
Description	A comma-separated list of SQL function names to register with the parser. If an R2RML view (using `rr:sqlQuery`) fails to parse, this option can be set to allow use of non-standard functions.

`unique.key.sets`

Default

Description For data sources that do not express unique constraints in their metadata, either because unique constraints are not supported or because the data source did not include some or all of the valid constraints for reasons such as performance concerns, this property is used to define additional constraints manually. The property value is a comma-separated list of keys that define unique rows in a table. Each key is itself a comma-separated list of schema-qualified columns, enclosed in parentheses. For example, if table APP.CUSTOMERS has an ID column that serves as a primary key and a pair of columns, FNAME and LNAME, that together are a unique key, the value to express that is: (APP.CUSTOMERS.ID),(APP.CUSTOMERS.FNAME,APP.CUSTOMERS.LNAME)

`default.mapping.include.tables`

Default
Description	A comma-separated list of tables to include when generating default mappings. If blank, mappings will be generated for all tables in the default schema for the connected user, plus any schemas listed in `sql.schemas`. Cannot be combined with `default.mapping.exclude.tables`.

`default.mapping.exclude.tables`

Default
Description	A comma-separated list of tables to exclude when generating default mappings. Mappings will be generated for all tables in the default schema for the connected user, plus any schemas listed in `sql.schemas`, except those tables listed in this option. Cannot be combined with `default.mapping.include.tables`.

`schema.in.generated.mappings`

Default	`false` (`true` for Elasticsearch)
Description	Whether to include the name of the schema (along with the table name) in the templates for IRIs when automatically generating mappings based on source database metadata. For Elasticsearch, setting this to true will cause the index name to be included in the template.

JDBC Properties

`jdbc.url`

Default
Description	The URL of the JDBC connection.

`jdbc.username`

Default
Description	The username used to make the JDBC connection.

`jdbc.password`

Default
Description	The password used to make the JDBC connection.

`jdbc.driver`

Default
Description	The driver class name used to make the JDBC connection.

`sql.dialect`

Default	Inferred from supported JDBC drivers. `ORACLE` for unsupported drivers.
Description	When using an unsupported JDBC driver, this option can be used to specify the format of the generated SQL. The options supported are `ATHENA`, `CASSANDRA`, `DB2`, `DERBY`, `ELASTICSEARCH`, `EXASOL`, `H2`, `HANA`, `HIVE`, `IMPALA`, `MSSQL`, `MYSQL`, `ORACLE`, `POSTGRESQL`, `REDSHIFT`, `SYBASE`, `TERADATA`

`sql.schemas`

Default
Description	A comma-separated list of schemas to append to the schema search path. This option allows R2RML tables and queries to reference tables that are outside of the default schema for the connected user.

`sql.default.schema`

Default
Description	Override the default schema for the connected user. Tables in the default schema may be referenced without qualification (`mytable` or `"mytable"` rather than `myschema.mytable` or `"myschema"."mytable"`).

Tomcat Connection Pool Properties

Additionally, connection pool properties for the built-in Tomcat connection pool are allowed. This set of additional allowed properties is listed in the Tomcat JDBC Connection Pool documentation. Stardog sets these connection pool defaults:

initialSize=3
testWhileIdle=true

# 4 hours
timeBetweenEvictionRunsMillis=14400000

validationQueryTimeout=10

To disable connection pooling, one can set the following connection pool properties

testOnBorrow=true
timeBetweenEvictionRunsMillis=0
maxIdle=0
minIdle=0

This may be uesful for troubleshooting some configurations.

Passing Options Directly to the JDBC Driver

Any options with the prefix ext. will be passed directly to the JDBC Driver. Tomcat connection pool properties do not need to be prefixed with ext.

Any unknown options will be ignored.

CSV Properties

`csv.separator`

Default	`,`
Description	A single-character separator used when importing tabular data files.

`csv.quote`

Default
Description	A single character used to encapsulate values containing special characters.

`csv.escape`

Default
Description	A single character used to escape values containing special characters.

`csv.header`

Default	`true`
Description	Should the import process read the header row? When headers are enabled the first row of the input file is used to retrieve the column names and mappings can refer to those column names. (`true`/`false`)

`csv.skip.empty`

Default	`true`
Description	Should empty values be skipped in the CSV file? If `true` no triples will be generated for templates that refer to a column with empty value. (`true`/`false`)

`csv.class`

Default
Description	Which class should be imported rows from CSV files be members of?

`csv.hash.function`

Default	`SHA1`
Description	Which hash function should be when the `#` notation is used to import CSV files? Any hash function supported by Stardog is allowed here, `SHA1`, `SHA256`, `SHA384`, `SHA512`, `MURMUR3`, `XX`, `MD5`.

MongoDB Properties

`mongodb.uri`

Default
Description	The URI for the MongoDB connection. Examples: `mongodb://localhost/mydb` or `mongodb+srv://myUserName:myP4ssw0rd@cluster0-kgprod.company.com/mydb`

Elasticsearch Properties

`elasticsearch.rest.urls`

Default
Description	Whitespace-delimited list of connection host/port values for Elasticsearch. Example: `server1:9200 server2:9200 server3:9200`

`elasticsearch.username`

Default
Description	Username for Elasticsearch connections

`elasticsearch.password`

Default
Description	Password for Elasticsearch connections

Cassandra Properties

`cassandra.contact.point`

Default
Description	The address of the Cassandra node(s) that the driver uses to discover the cluster topology. Example: `cassandra.abc.com`

`cassandra.keyspace`

Default
Description	The Cassandra keyspace to use for this session

`cassandra.username`

Default
Description	The username for the Cassandra cluster

`cassandra.password`

Default
Description	The password for the Cassandra cluster

`cassandra.allow.filtering`

Default	`false`
Description	Whether to include the `ALLOW FILTERING` clause at the end of Cassandra CQL queries. Not recommended for production use.

SPARQL Engine/Service

`sparql.url`

Default
Description	SPARQL query endpoint/connection string with database specified, i.e. `http://myhost:26023/testdb/query`

`sparql.username`

Default
Description	The username to access the SPARQL endpoint.

`sparql.password`

Default
Description	The password to access the SPARQL endpoint.

`sparql.graphname`

Default
Description	The graph name on SPARQL endpoint that needs to be mapped as virtual graph.

`sparql.statsbasedoptimization`

Default	`true`
Description	The boolean value to enable/disable statistics based optimization while accessing SPARQL endpoint. By default its always enabled.

Overview
Virtual Graph Properties