[
https://issues.apache.org/jira/browse/COMMONSRDF-6?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14518614#comment-14518614
]
ASF GitHub Bot commented on COMMONSRDF-6:
-----------------------------------------
Github user ansell commented on a diff in the pull request:
https://github.com/apache/incubator-commonsrdf/pull/10#discussion_r29307087
--- Diff: api/src/main/java/org/apache/commons/rdf/api/RDFTermFactory.java
---
@@ -60,34 +54,28 @@ default BlankNode createBlankNode() throws
UnsupportedOperationException {
}
/**
- * Create a blank node based on the given identifier.
- *
- * All BlankNodes created using this method with the same parameter
for a
- * single instance of RDFTermFactory MUST be equivalent. Ie,
- * {@link BlankNode#equals(Object)} MUST return true. A BlankNode
object
- * created through the {@link RDFTermFactory#createBlankNode()} method
must
- * be universally unique, and SHOULD contain a {@link UUID} as part of
its
- * {@link BlankNode#internalIdentifier()}.
- *
- * A BlankNode object created through the
- * {@link RDFTermFactory#createBlankNode(String)} method must be
universally
- * unique, but also produce the same {@link
BlankNode#internalIdentifier()} as any
- * previous or future calls to that method on that factory with the
same
- * parameters. In addition, it SHOULD contain a {@link UUID} as part
of its
- * {@link BlankNode#internalIdentifier()}, created using
- * {@link UUID#nameUUIDFromBytes(byte[])} using a constant salt for
each
- * instance of {@link RDFTermFactory}, with the given identifier
joined to
- * that salt in a consistent manner.
- *
- * BlankNodes created using this method with the same parameter, for
- * different instances of RDFTermFactory, SHOULD NOT be equivalent.
- *
- * @param identifier A non-empty, non-null, String that is unique to
this blank
- * node in the context of this {@link
RDFTermFactory}.
- * @return A BlankNode for the given identifier
- * @throws UnsupportedOperationException If the operation is not
supported.
+ * Create a blank node based on the given name.
+ * <p>
+ * For a particular instance of <code>RDFTermFactory</code>, all
+ * {@link BlankNode}s created using this method with the same
+ * <code>name</code> parameter MUST be equivalent according to
+ * {@link BlankNode#equals(Object)},
+ * The returned BlankNode MUST NOT be equal to any other
--- End diff --
This sentence could be cleaned up. In particular, it could be emphasised
that it only applies when the sentence above does not apply. Ie, when the name
parameter is different, the BlankNode object must be not equals.
> Contract around the internal string of a blank node
> ----------------------------------------------------
>
> Key: COMMONSRDF-6
> URL: https://issues.apache.org/jira/browse/COMMONSRDF-6
> Project: Apache Commons RDF
> Issue Type: Improvement
> Reporter: Stian Soiland-Reyes (old)
> Fix For: 0.1
>
>
> From https://github.com/commons-rdf/commons-rdf/issues/56
> afs:
> {quote}
> RDF 1.1 says "IRIs, literals and blank nodes are distinct and
> distinguishable." [my emphasis]
> http://www.w3.org/TR/rdf11-concepts/#section-rdf-graph
> This is a consequence of RDF being an abstract syntax - there is no
> logic/entailment at this level - it was true in RDF 1.0 but now it is
> explciitly stated in RDF Concepts.
> Distinguishable blank nodes mean that unique characteristics need to align to
> the Java identity contract.
> At least, the same (= RDFTerm.equals) blank node, even when different java
> objects, must have the same internal string. (.equals)
> It's a one-way implicition: same internal string does not imply equality so
> this works across independent implementations.
> An extreme implementation is to always return the same internal string (may
> not be helpful but should be legal).
> {quote}
> afs:
> {quote}
> This also related to the proposed {{BlankNode.ntriplesString()}}.
> The choice of output string is dependent on the writing process. It only
> needs to be unique across the file being written. A choice for output is
> short forms like ":b0", ":b1" etc.
> The ntriples output form is not a unique property of the blank node. I think
> we should not include ntriplesString in the core common API.
> {quote}
> stain:
> {quote}
> Not sure what this is proposing, but :-1: to remove BlankNode.ntriplesString
> - and :+1: to improve the contract text for BlankNode.
> I found ntriplesString very useful as it becomes an interoperability point
> and have (largely) predictable outputs.
> The commons RDF API stays very close to the rdf11-concepts
> http://www.w3.org/TR/rdf11-concepts/ , which I like. The ntriplesString are
> however trivial to implement - and almost all implementations are probably
> going to have something like that anyway. I never liked much that the name
> doesn't include get - but I guess that is because it is a derived value and
> might need further calculations.
> The only contentious part is in BlankNode - so perhaps add a specialization
> of ntriplesString that clarifies the pitfalls here (as we did with equals).
> The long paragraphs of BlankNode on the top does not currently help to
> clarify this.
> See the simple implementation of BlankNode for one simple way to deal with
> those "non-ntriples-valid internal identifiers".
> Always keeping an internal UUID field or similar is another - implementations
> can decide on what is most natural to their implementations - they probably
> have already dealt with this already, although possibly not within their
> equivalent of the BlankNode class. The BlankNode is also free to keep an
> internal reference to the Graph or "local scope" and use that to generate
> identifiers.
> There is no requirement anywhere for Blank Node identifiers to always be
> re-generated in serialization - this is simply a liberty that is available. A
> serializer based on Commons RDF can still do that - he can simply ignore
> BlankNode.ntriplesString and create a temporary Map from internalIdentifier
> to b1, b2, etc. I do however not see why we need to REQUIRE a serializer do
> such an operation - that is taking this API beyond its scope and into "best
> practice" (in which case we would also deal with prefixes, preserving prefix
> names, canonicalizing URIs, etc).
> As an example of the current strength, I was able to write an N-triples
> serializer in simple by just concatenating the ntriplesString of the
> components from TripleImpl.toString and then just joining with \n:
> This is powerful - for nothing else it's great for debugging. I am not
> proposing to add ntriplesString() for Triple, as it might need to be much
> closer to the Graph - but at least RDFNode.toString() could have a default
> method that calls ntriplesString() (which is 200 times more useful than
> LiteralImpl 2bd85b1f529302f9 from Object.toString :) )
> {quote}
> afs:
> {quote}
> Some display string is useful but reading the contract for ntriplesString, it
> is not (just) for display purposes. c.f. Java toString. There is a different
> in escaping. I see that TripleImpl.toString does not do syntax escaping.
> Providing a readable RDFNode.toString() would separate the development dsplay
> concerns (e.g. no escapes maybe) from serialization concerns.
> Some RDF systems implement blank nodes from a sequence (e.g. Mulgara).
> Actually that policy can be quite convenient for debugging development.
> We could include N-Triples in commons-rdf but to me v1 should targetted as
> "use RDF data". Parsing and serialization is the concern of the
> implementation. The simple impl is one such example, not a new RDF system (is
> it?:-)
> {quote}
> ansell:
> {quote}
> I commented on the pull request to remove some of the tests that test or rely
> on the BlankNode internal identifier structure, particularly that it be a
> valid n-triples identifier. However, those tests made it into the merged
> version because it was otherwise basically okay and we are continually
> evolving anyway so there is no need to have perfect pull requests at this
> stage. I will review and merge #55 and then work on any further cases that we
> may not be testing for yet.
> I am all for defining/clarifying the contract for .toString in the API, even
> if it says that there is no specific escaping or formatting done on the
> output of .toString.
> Supporting N-Triples in the base API seems to be natural for two reasons to
> me. Firstly, it is the simplest syntax, so it doesn't require any particular
> optimisations and Triples can be streamed out without relying on a particular
> framework or serialiser. Secondly, for a long time it has been the sole
> established test case format for RDF, although it is defined on its own for
> RDF-1.1, so it is a natural single serialisation to support.
> As long as the output of ntriplesString is defined to be implementation and
> local scope specific for BlankNodes (no confusion with IRI or Literal), I am
> fine with having it. Given the number of times the BlankNode API references
> "local scope" right now, we are unlikely to have more users commenting that
> it is unusual than we already have had for the last 10 years with RDF-1.0.
> {quote}
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
