Specific Accessor Implementations

Prajna comes with a number of accessors. Developers may use these accessors for common data sources, and add domain-specific behavior with Field Handlers.


The CommonMLAccessor retrieves data from standard Markup Language formats for each of the data structure types. It reads GraphML for graph data, and TreeML for graphs. It does not support grids or datasets yet.


The DbpediaAccessor retrieves records from Dbpedia. It queries for records relating to a particular subject or topic, and retrieves data from the underlying RDF triple-store through a SPARQL query.


The DelimitedAccezsor retrieves records from a delimited file, such as one that delimits the fields by tabs or commas. The first line of the file is expected to be the column names. The delimiter may be any character.


The FusionAccessor takes results from other accessors, and fuses them into a common set of records. The other accessors should be specified in the configuration file, and the field mappings transform the records from the underlying accessors.

In order to retrieve the appropriate records and fields from the underlying accessors, the field references for the FusionAccessor are in the form accessor.template.field. If the field portion of the field reference is omitted, the name of the record is retrieved, and used to identify which records should be merged. Example:

This template retrieves the records from the accessor named winelist using the template wines to determine the individual records. It then


The JdbcAccessor retrieves records from a standard SQL database, such as Oracle, Sybase, or MySQL. The connection to the database may either be provided, or a developer can pass the connection information with the setInitParameters method.

For a particular data template, the recordIdentifier attribute defines the table containing the records. The JdbcAccessor retrieves the rows from the table, plus any other tables needed. A field descriptor can specify a lookup table, which is used if the values are indexed.


The SolrAccessor retrieves records from a Solr website. Solr is an open source enterprise search server from the Apache foundation, offering faceted search and other capabilities. The accessor queries the service and constructs records from the results. The URL of the service must be specified as an initialization parameter.