Hi Andy, Thanks for your helpful replies.
Some brief follow-up: 1. I thought that D2RQ could present a virtual RDF graph based on SQL DB only. Can it be customized (via some kind of adapter plug-in) to handle NoSQL DB? Thanks again. -paul Technology Architect Syncsort Data Protection "Heideggerian Magneto Reluctance Algorithms risk Sinusoidal Depleneration" On Nov 23, 2012, at 10:17 AM, "Andy Seaborne" <[email protected]> wrote: > On 22/11/12 19:18, Bell, Paul M. wrote: >> Hi, >> >> I have a few questions about Jena's storage and query capabilities. >> >> >> 1. Jena seems to support RDF stores of these types: in-memory, SQL, >> native tuple store (TDB), and "custom." How are these stores >> initially populated, i.e., does Jena offer some kind of "load >> facility" that reads from, say, SQL and writes RDF? > > The Jena APi can be used on any store so once code has got a hanle on > the store (dataset, model) everythign is the same. > > Jena itself does not offer a legacy SQL to RDF path - theer are tools > such as D2RQ that offer that as a dump or as a live connection back to > the original (and live) data. Look for R2RML tools - R2RML is the W3C > standard for this. > > D2RQ offers R2RML or soon will do (it's not from the Apache Jena > project, it used Jena IIRC). > > There are commercial tools. > >> 2. If there is such a load facility, can it read from a NoSQL DB, >> e.g., MongoDB, and write to the RDF store? > > Not in Jena per se. A key stap is mapping the data to an RDF data > model. That can be simple (close to being a RDFization of the NoSQL > store), or complex (presenting higher level modelling concepts). > >> 3. Suppose that a SPARQL query needed to reference non-triplestore >> data. Can Jena call into a custom "adapter" that reads these >> non-triplestore data, receive these data from the adapter, and >> incorporate them into its query resolution? > > See R2RML - that would give a SPARQL interface to an existing SQL DB. > >> A more general question: what are some common practices concerning >> RDF store consistency? I suppose that most RDF stores are initially >> populated from SQL stores. Given the likely volatility of SQL stores, >> doesn't this mean that the RDF store can quickly grow stale, i.e., it >> might contain relationships among resources that no longer exist? How >> is this consistency issue handled in the real world? > > Not sure that most stores are populated from SQL. > > If liveness matters, a dynamic connection such as D2RQ offers up-to-date > access. > > Andy > >> >> >> >> Thanks for your help. >> >> >> >> Cordially, >> >> >> >> Paul ATTENTION: ----- The information contained in this message (including any files transmitted with this message) may contain proprietary, trade secret or other confidential and/or legally privileged information. Any pricing information contained in this message or in any files transmitted with this message is always confidential and cannot be shared with any third parties without prior written approval from Syncsort. This message is intended to be read only by the individual or entity to whom it is addressed or by their designee. If the reader of this message is not the intended recipient, you are on notice that any use, disclosure, copying or distribution of this message, in any form, is strictly prohibited. If you have received this message in error, please immediately notify the sender and/or Syncsort and destroy all copies of this message in your possession, custody or control.
