Database Reference
In-Depth Information
predicate and object in a RDF triple) provided as parameters, in the format
requested. The exporting result is inline in the response.
- ldimport: Apart from the indirect importing imposed by a specific relational-to-
LD mapping (see addR2RMLMappings method), a data provider can directly
import RDF data into the system through the use of this method. To this end,
the RDF data to be imported are either inline in the request or a URL must
be provided from which they can be fetched. Import execution can be blocking
or non-blocking, where the size of the imported data can be the determinant
factor in the selection of one of these two import types.
- import status: When a non-blocking import request has been made by a data
provider, the status of the respective import can be inquired through calling
this method.
Each method is accessed via a specific URL (which has the same prefix
but just the postfix is modified to match the name of the method - e.g., for
ldquery ,theURLis: https://portal.ingeoclouds.eu/ingeoclouds-api/linkeddata/
rest/ld/ldquery ) . In case user input is wrong, meaningful exception messages
are returned to the user (e.g., wrong SPARQL syntax). A user-friendly doc-
umentation of LMS has been produced in HTML format via Enunciate and is
accessible in a specific URL 19 . Enunciate was also exploited to produce the inter-
face definition documents (WADL and WSDL) and the required XSD schemas.
LMS exploits the following java modules: (a) the Sesame RDF Data Manage-
ment API which provides bridge methods between a user application (which
is LMS in this case) and an underlying Triple Store, (b) the Virtuoso's JDBC
driver (for properly exploiting Virtuoso via the Sesame API), and (c) Jersey (for
REST-based realization of LSM).
3.3 Virtuoso Universal Server
Virtuoso Universal Server is a hybrid of a database engine and a middleware
which combines the functionality of a traditional RDBMS, an ORDBMS, a RDF-
Store, a virtual database, a web application server and a file server. It maps to a
single-threaded server process supporting multiple Web and Internet protocols,
such as HTTP, HTTPs, WebDav, SOAP, UDDI, SPARQL and SPARUL. More-
over, for enabling the development of database-based applications and system
integration, Virtuoso has implemented a wide variety of industry standard data
access APIs, such as ODBC, JDBC, OLE DB, and ADO .NET. Virtuoso Uni-
versal Server can be exploited either in a standalone, clustered or cloud-based
manner. As the latter two exploitation ways are not free, we have relied on the
first one to build our system and have realized update synchronization mecha-
nisms to enable its transformation into a clustered set of Triple Stores via also
exploiting cloud-based technologies.
Virtuoso supports not only the querying and updating of LD through the
SPARQL language but also their complete management by offering various low-
level SQL functions that can be exploited. In addition, from version 7 and on,
19 https://portal.ingeoclouds.eu/ingeoclouds-api/linkeddata/ .
 
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