The mixer is a maven project born with the intent of testing OBDA systems. This version (1.1.0) interacts with the OBDA system through a Java API interface. Such interface is currently implemented for the latest stable version (v1.18) of the Ontop ODA system. Mixer gives access to fine-grained and OBDA-specific metrics such as the_query unfolding time_ (i.e., the time spent in unfolding the mappings definitions and producing the SQL translation for the input query) or the query rewriting time (i.e., the time spent in rewriting the input query so as to take into account for the axioms in the ontology).
OBDA-Mixer runs a set of SPARQL queries (query mix) over an OBDA system. A typical query is an instance of a SPARQL query template, where a SPARQL query template is a SPARQL query with placeholders. Such templates will be instantiated by obda-mixer at runtime with values taken from a database of choice. For instance, a query with placeholders is:
PREFIX npdv: <http://sws.ifi.uio.no/vocab/npd-v2#>
SELECT DISTINCT ?licenceURI ?interest ?date
WHERE {
?licenceURI a npdv:ProductionLicence .
[ ] a npdv:ProductionLicenceLicensee ;
npdv:dateLicenseeValidFrom ?date ;
npdv:licenseeInterest ?interest ;
npdv:licenseeForLicence ?licenceURI .
FILTER(?date > "${1:licence_licensee_hst.prlLicenseeDateValidFrom}"^^xsd:date)
}
In the query above, the placeholder is ${1:licence_licensee_hst.prlLicenseeDateValidFrom}. At runtime, obda-mixer instantiates this placeholder with values from the column prlLicenseeDateValidFrom in table licence_licensee_hst.
The Java API interface is currently implemented for the Ontop system. To implement your own interface for an OBDA system of your choice, refer to How To Instantiate the Mixer Interface with an OBDA System through the Java API