This version of Redland is a major update to 0.9.12 changing the node class. librdf_node objects are now immutable once created, higher-level language APIs no longer have deal with sharing or copying internals, some additional API support for parsing content from strings.
This includes the stable and complete version 0.9.12 of the Raptor parser which supports all of the revised RDF/XML syntax.
Initial work was added on an ECMA CLI interface using the C# ("C sharp") language.
Blank nodes generated by parsing the syntaxes are now generated more unique (not guaranteed) based on the Redland startup time and a serial number.
The Perl, Python and Java APIs now always return new nodes and statements removing the need to consider sharing at this level. This means that the following operation is legal in Perl, Python and Java:
# perl
$n=RDF::Redland::Node->from_uri("http://example.org/foo");
$s=new RDF::Redland::Statement($n, $n, $n);
$model->add($s);
# python
n=RDF.Uri("http://example.org/foo")
s=RDF.Statement(n, n, n) # n is used as a resource RDF.Node here
model.add_statement(s)
Several improvements were made to the building and configuring including a better attempt to find matching Sleepycat/Berkeley DB header and library files (and support BDB up to 4.1), searching for installed Java JDKs and Tcl headers. Each of the language interfaces can be individually enabled to be build, tested and installed with the main C library.
The librdf_node class was modifed to make objects immutable once constructed, they cannot be modified. The following set methods were consequently removed.
The following utility methods were added (covering all the librdf_node_get_type values):
(These are reflected into the same methods on the Perl, Python and Java node classes)
LIBRDF_NODE_TYPE_LI as returned by librdf_node_get_type was deleted, it was never used.
To support datatyped literals, the following method was added:
Added librdf_model_sync to sync the model to the backing store.
Added librdf_model_as_stream and librdf_model_context_as_stream to replace librdf_model_context_serialise and librdf_model_context_serialize respectively. This was done both to reduce the confusion with the librdf_serializer class and the mixture of US/UK spelling of that word. The old functions will remain for now.
Added librdf_parser_parse_string_as_stream and librdf_parser_parse_string_into_model to allow parsing content from strings.
Added librdf_statement_is_complete to test if a statement has all the subject, predicate and object fields assigned. Partial statements cannot be added to a model but can be used in matching statement queries with librdf_model_find_statements.
Added librdf_storage_sync to sync the backing store. (This is slightly internal to Redland, you should not be calling this directly)
Updated to make the object constructors less verbose and to allow Redland URI objects and native perl URIs to be used in place of Redland Nodes where convienent (such as in making Statements). All existing code should work but can be shortened. A new --with-perl configure argument to enable the perl interface.
A major update to use Python 2.2+ idioms and features by Edd Dumbill with help from Matt Biddulph for unit tests. A new --with-python configure argument to enable the python interface. Edd wrote the following change log.
General changes
Additions for the new API calls as outlined above (such as model/storage sync, parsing from strings etc.). New configure argument --with-jdk to pick the JDK in order to find the JNI headers. See the java API page for details.
Updates in configuring and building these interfaces and new --with-php, --with-ruby and --with-tcl configure arguments. See the corresponding API pages and installation documentation for details. Tcl now tries to guess the includes directories.
This version of Redland is a major update to 0.9.11 incorporating a much more improved, complete and stable version 0.9.7 of the Raptor parser and a significant new feature, contexts. The high-level language APIs received some updates and the start of two new languages APIs were added: Ruby and PHP.
Several incompatible API changes were made in this release that effect the C interface and all the higher level language APIs. These were made to support contexts and to fix some inconsistencies in the interface about object ownership.
The persistent storage format was changed to support RDF typed literals and this requires an upgrade of any existing Berkeley/Sleepycat DB stores created by Redland 0.9.11 or earlier. A utility redland-db-upgrade is provided that will create an updated store from an existing one.
A Perl script utils/update-api-0912.pl can help automate the API changes as far as possible or warn about those that cannot be automatically updated.
This feature allows a Node to be given whenever a statement is
added to a model which can can be retrieved from any model query that
returns answers as an Iterator of Nodes or a Stream of Statements.
Both of these classes gained a new method get_context
that returns the original Node that was given when the statement
corresponding to the answer was added to the model.
The context node can also be used to add and remove sets of statements to/from a model, and each statement with a given context node can be listed as a stream of statements.
Adding this feature required substantial internal changes to these two classes and the internal storage apis and implementations along with moderate code changes at the application level, which are described below.
This feature can be used for the following (not an exhaustive list):
The Iterator
get_next method was split into get_object
always returning a pointer to a shared object and the
next method to advance the iterator.
The get_object method is generally called
current in the higher level language APIs.
(Iterator and Stream now have consistent method names; they may be merged in future.)
The get_object method now always returns a pointer to
a shared object. If this object is needed outside the scope of an
iteration, it must be copied, which for Nodes is the copy constructor
librdf_new_node_from_node.
C example for Redland 0.9.11 and earlier:
while(!librdf_iterator_end(iterator)) {
node=(librdf_node*)librdf_iterator_get_next(iterator);
/* do something with the node */
}
Redland 0.9.12:
while(!librdf_iterator_end(iterator)) {
node=(librdf_node*)librdf_iterator_get_object(iterator);
/* do something with the node */
librdf_iterator_next(iterator);
}
A new method get_context was added returning a Node
for the context of the original Statement that generated the Iterator
Node.
C Iterator context example:
while(!librdf_iterator_end(iterator)) {
node=(librdf_node*)librdf_iterator_get_object(iterator);
context_node=(librdf_node*)librdf_iterator_get_context(iterator);
/* do something with the node and its context */
librdf_iterator_next(iterator);
}
The Model
add_statement method no longer takes ownership of the
passed in statement object. The caller now retains ownership and can
reuse the statement several times and has responsibility for freeing it
if need be (when it isn't shared).
C example for Redland 0.9.11 and earlier:
librdf_model_add_statement(model, statement);
Redland 0.9.12:
librdf_model_add_statement(model, statement); librdf_free_statement(statement);
C streaming statement example for Redland 0.9.11 and earlier:
while(!librdf_stream_end(stream)) {
librdf_statement *statement=librdf_stream_next(stream);
/* This statement is new, so could be added directly */
librdf_model_add_statement(model, statement);
}
Redland 0.9.12:
while(!librdf_stream_end(stream)) {
librdf_statement *statement=librdf_stream_get_object(stream);
/* This statement is now shared so can still be just added */
librdf_model_add_statement(model, statement);
}
librdf_model_add_string_literal_statement lost the
xml_space argument.
A new method was added to add a Statement with an RDF datatyped literals object:
int librdf_model_add_typed_literal_statement(librdf_model* model,
librdf_node* subject,
librdf_node* predicate,
char* string, char *xml_language, librdf_uri *datatype_uri);
This should be used in preference to
librdf_model_add_string_literal_statement which remains
in the API as a wrapper around the above.
New methods were added to add, remove and list Statements to contexts.
/* Add a single statement to the model with context */
int librdf_model_context_add_statement(librdf_model* model,
librdf_node* context, librdf_statement* statement);
/* Add all statements on the stream to the model with context */
int librdf_model_context_add_statements(librdf_model* model,
librdf_node* context, librdf_stream* stream);
/* Remove a single statement from the model with the given context */
int librdf_model_context_remove_statement(librdf_model* model,
librdf_node* context, librdf_statement* statement);
/* Remove all statements from the model with given context */
int librdf_model_context_remove_statements(librdf_model* model,
librdf_node* context);
/* List all statements in the model with the given context */
librdf_stream* librdf_model_context_serialize(librdf_model* model,
librdf_node* context);
The Node class gained a new constructor:
librdf_node* librdf_new_node_from_typed_literal(librdf_world *world,
const char *string, const char *xml_language, librdf_uri* datatype_uri);
that should be used in preference to
librdf_new_node_from_literal which remains in the API as
a wrapper around the above.
librdf_node_new_nodefrom_literal lost the
xml_space argument.
The Parser class has an updated
Raptor parser
version 0.9.7 - parsers named raptor for RDF/XML
(MIME Type application/rdf+xml)
and ntriples for N-Triples. See the
Raptor NEWS
for the detailed changes since 0.9.5 in the last release of Redland.
The Java SiRPAC parsers sirpac-stanford,
sirpac-w3c and the W3C LibWWW parser libwww
have been removed. Raptor replaces them.
The Serializer class gained a new method:
int librdf_serializer_serialize_model_to_file(librdf_serializer* serializer,
const char *name, librdf_uri* base_uri, librdf_model* model);
This writes the serialized model to a filename
(rather than a file handle as done by
librdf_serializer_serialize_model)
which is easier to use from higher level language APIs until a
cross-language I/O abstraction is available.
The class gained an RDF/XML serializer that can be called
either by the name rdfxml or the
MIME Type application/rdf+xml. The
examples in each language have been updated to demonstrate
using this.
The built in storage factories (memory,
hashes) now both support contexts. These are enabled by
adding the storage option contexts='yes' to the options
string. The hashes storage additionally supports indexing predicates
as an extra hash which can be enabled with index-predicates='yes'.
This makes triple queries of the form
(subject unknown, predicate known, object unknown) fast.
C Example of creating a 0.9.12 storage that does contexts using on-disk Berkeley/Sleepycat DB:
storage=librdf_new_storage(world,
"hashes",
name,
"hash-type='bdb',write='yes',new='yes',contexts='yes'");
The Stream
next method was split into get_object
always returning a pointer to a shared Statement and the
next method to advance the iterator.
The get_object method is generally called
current in the higher level language APIs.
(Iterator and Stream now have consistent method names; they may be merged in future.)
C example for Redland 0.9.11 and earlier:
while(!librdf_stream_end(stream)) {
statement=(librdf_statement*)librdf_stream_next(stream);
/* do something with the statement */
}
Redland 0.9.12:
while(!librdf_stream_end(stream)) {
statement=(librdf_statement*)librdf_stream_get_object(stream);
/* do something with the statement */
librdf_stream_next(stream);
}
A new method get_context was added returning a Node
for the context of the Statement.
C Stream context example:
while(!librdf_stream_end(stream)) {
statement=(librdf_statement*)librdf_stream_get_object(stream);
context_node=(librdf_node*)librdf_stream_get_context(iterator);
/* do something with the statement and its context node */
librdf_stream_next(stream);
}
The Perl interface
moved to the RDF::Redland package (the RDF
namespace was deprecated in 0.9.11).
The interface was updated to receive Redland error and warning
messages callbacks. These can be set using the
RDF::Redland::set_error_handler
and RDF::Redland::set_warning_handler subroutines
taking a subroutine argument. They are called with a single
scalar argument which is the Redland message.
The interface was updated to match the Interator and Stream changes described above.
Perl iterator example for Redland 0.9.11 and earlier:
while(!$iterator->end) {
my $node=$iterator->next;
# do something with the node
}
Redland 0.9.12:
while(!$iterator->end) {
my $node=$iterator->current;
# do something with the node
$iterator->next;
}
Perl stream example for Redland 0.9.11 and earlier:
while(!$stream->end) {
my $statement=$stream->next;
# do something with the statement
}
Redland 0.9.12:
while(!$stream->end) {
my $statement=$stream->current;
# do something with the statement
$stream->next;
}
Perl example of using the Serializer class:
# Use any rdf/xml parser that is available
my $serializer=new RDF::Redland::Serializer("rdfxml");
$serializer->serialize_model_to_file("output.rdf", $uri, $model);
The Python interface gained pydoc comments, along with an HTML derived version.
The interface was updated to receive Redland error and warning messages callbacks as python exceptions. These can be caught using the standard python try {} catch {} blocks.
The interface was updated to match the Interator and Stream changes described above.
Python iterator example for Redland 0.9.11 and earlier:
while not iterator.end():
node=iterator.next()
# do something with the node
Redland 0.9.12:
while not iterator.end():
node=iterator.current()
# do something with the node
iterator.next()
Python stream example for Redland 0.9.11 and earlier:
while not stream.end():
statement=stream.next()
# do something with the statement
Redland 0.9.12:
while not stream.end():
statement=stream.current()
# do something with the statement
stream.next()
Python example of using the Serializer class:
# Use any rdf/xml parser that is available
serializer=RDF.Serializer()
serializer.serialize_model_to_file("output.rdf", model)
The Java classes were updated to have
a finished() method that the user can call to cleanup
objects replacing the rather useless Java finalize()
method that gives no guarantees to when it is called.
The Java API is still experimental and may change further.
Release notes for 0.9.11 and earlier are in the NEWS page or ChangeLog
Copyright 2003 Dave Beckett, Institute for Learning and Research Technology, University of Bristol