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|Monitoring the database|
The predicate rdf_monitor/2
allows registrations of call-backs with the RDF store. These call-backs
are typically used to keep other databases in sync with the RDF store.
library(library(semweb/rdf_persistency)) monitors the RDF
store for maintaining a persistent copy in a set of files and
library(library(semweb/rdf_litindex)) uses added and
deleted literal values to maintain a fulltext index of literals.
literal(Arg)of the triple's object. This event is introduced in version 2.5.0 of this library.
end(Nesting). Nesting expresses the nesting level of transactions, starting at `0' for a toplevel transaction. Id is the second argument of rdf_transaction/2. The following transaction Ids are pre-defined by the library:
Mask is a list of events this monitor is interested in.
Default (empty list) is to report all events. Otherwise each element is
of the form +Event or -Event to include or exclude monitoring for
certain events. The event-names are the functor names of the events
described above. The special name
all refers to all events
assert(load) to assert events originating from rdf_load_db/1.
As loading triples using rdf_load_db/1
is very fast, monitoring this at the triple level may seriously harm
This predicate is intended to maintain derived data, such as a journal, information for undo, additional indexing in literals, etc. There is no way to remove registered monitors. If this is required one should register a monitor that maintains a dynamic list of subscribers like the XPCE broadcast library. A second subscription of the same hook predicate only re-assignes the mask.
The monitor hooks are called in the order of registration and in the
same thread that issued the database manipulation. To process all
changes in one thread they should be send to a thread message queue. For
all updating events, the monitor is called while the calling thread has
a write lock on the RDF store. This implies that these events are
processed strickly synchronous, even if modifications originate from
multiple threads. In particular, the
... updates ... end sequence is never interleaved with
other events. Same for