Although i have a little bit of experience in developing dynamic websites using ASP technologies, but I am new to semantic web programming, and i intend to implement a website based on semantic web technology.I would like to develop a search engine, where a web user can query for keywords from the backend RDF triple store.I want to implement the website using Java and JSP.I have following questions:
I am currently studying Jena framework and SPARQL to start with,but
i am not sure what other technologies i need to study in order to
implement the website.
What is the difference between RDF and OWL, I have gone through a
lot of web resources but i am still confused.As per my understanding
RDF and OWL both define relationship between concepts but OWL is
more rich in terms of defining relations.
What is meant by different OWL Vocabularies like FOAF, SIOC etc.Why
do we need these vocabularies?
What exactly is the purpose of Virtuso Open Link
Software(http://ods.openlinksw.com/dataspace/dav/wiki/Main/VirtJenaProvider)
Any help would be highly appreciated.
Thanks!
I would definitely like to be kept up to date of your progress. I'm not experienced with java or jsp. I wonder if this could be done in php? I know that some work has been done in python on this kind of thing.
There are some extensions to drupal that work with these semantic web technologies and Semantic Media Wiki is good too.
Check out this and the related links at the bottom. The difference between microformats and vocabularies can be difficult to understand but I think there is a difference, say between a vocabulary like FOAF and a microformat like hCard, hCalendar or hResume. Oh, the link:
http://en.wikipedia.org/wiki/FOAF_(software)
Anyway these related terms are included.
Thanks,
Bruce
http://futurewavedesigns.com
Re: your first question - why do you want to use RDF to implement a keyword search? Keyword search isn't semantic, and there are many established frameworks and APIs for keyword search, such as Lucene.
Re: your second question, comparing RDF and OWL is comparing apples and oranges. RDF is basically for declaring data, but OWL is a layer on top of RDF that is for declaring ontologies (schemas). A more meaningful comparison would be between RDFS (RDF Schema) and OWL, which both address the ontology layer.
Example:
In RDF you might state that John Smith is a Person who hasAge "42" and is marriedTo Jill Smith.
In RDFS or OWL you would declare that Person is a class, hasAge is a property (with domain of Person and range of xsd:integer) and marriedTo is a property (with domain and range of Person).
In OWL you can also declare that marriedTo is a symmetric property (if A is marriedTo B, then B must be marriedTo A). RDF isn't this powerful, so you can't make this particular statement, so can't make inferences about symmetric properties etc.
Related
I need your help with the following situation.
I have a local relational database that contains information about several places in a city. These places could be any kind of attraction: Museum, a cathedral, or even a square.
As an example I have information about "Square Victoria" (https://en.wikipedia.org/wiki/Victoria_Square,_Montreal)
A simple search in google gave me the wikipedia URL above. But I want to be able to do it programmatically.
For each place in the database I have also its category (square, museum, church, ....). These categories are local only and do not match any standardized categorization.
My goal is to improve this database by associating each place to its dbpedia URI.
My question is what is the best way to do that? I have some theoretical background about Semantic Web technologies but I don't have yet the practice skills to determine how to do that.
More specific questions:
Is it possible to determine the dbpedia URI using sparql only?
If it is not possible to do it with sparql only, what other technologies would I need to be able to accomplish that?
Thank you
First of all I would recommend, if you have not done it yet, to have a look at wikidata. This project is a semantic extension to wikipedia, but contrary to dbpedia, the data is not extracted from wikipedia, it is created by contributors, and therefore appears (or will appear as the project is still growing) to be more relevant.
The service offers many solutions to access data (including a Sparql endpoint), and it's main advantage is that the underlying software is mediawiki, same used for wikipedia and other Wikimedia foundation projects. The mediawiki API offers an Opensearch option that should allow you to search more efficiently that Sparql queries.
Putting everything together, I think it might be worth having a look at wikidata + wikipedia API to get pivot data to align you local database.
No direct answer but I hope that will help.
I'm new in "ontology world". I've been practicing Protegé and ontologies for 2 months and now I would like to understand (and if it is possible to create) a reasoner. But I don't know what is its structure, the language used by it and so on.
Can you please me provide me a piece of information and something to read? Thank you.
The task of a reasoner is to produce inferences. Standard reasoning tasks are consistency check, realization, instance check and satisfiability. You can find all these defined in a number of books and articles about description logic.
Protege uses the OWL API to interface to reasoners so they are implementations of OWLReasoner. Not all of them are written in Java (e.g., FaCT++ is written in C++).
They are quite complex systems, so describing how to implement one takes chapters - too big for an answer here.
I'd recommend exploring the source code of a few of them. Open Source ones, off the top of my head: HermiT, FaCT++, Pellet, JFact, ELK.
I'm working on an OWL ontology and I need some specific issues
I only need ontology schema (TBox) and I got lost, what are the operations that can be
completed using reasoning and sparql and OWL API?
More specifically, I need the following:
1- check cardinalities between classes and properties.
2- find subsumption relationships for a specific class.
3- check whether specific facts hold (e.g. are two classes are disjoint)
4- find the paths (a class-property series) between a set of classes.
What each of reasoning, sparql and OWL API used for? and which one is suitable for my situation?
Actually I don't know how to start and what technique to use.
In addition. Would you please refer me to some reference?
Thanks.
Number 1 is not clear: do you want to know which cardinality axioms are asserted? This can be done without a reasoner. Number 4 is a bit vague as well, can you provide an example?
2, 3 and 5 require a reasoner to be perform accurately.
A reasoner is a program that will explicit implicit information: subsumption, realisation, consistency checks are all operations for which a reasoner is needed. In your tasks, subsumption is clearly needed.
OWLAPI is a Java API to manipulate OWL ontologies; in your case, it could be useful to write the connecting code to use a reasoner for your tasks. Compatible reasoners are Pellet, HermiT, FaCT++, and a few more.
SPARQL is an RDF query language. OWLAPI does not support it. You could use it for your tasks, but they look more OWL oriented than RDF oriented to me. Jena is a Java library supporting RDF, OWL, SPARQL and interfaces with reasoners such as Pellet. Depending on how you decide to solve the above tasks, it might fit more of your requirements than the OWLAPI.
Jena tutorials:
https://jena.apache.org/tutorials/index.html
OWLAPI documentation:
https://github.com/owlcs/owlapi/wiki/Documentation
How do we know which vocabulary/namespace to use to describe data with RDFa?
I have seen a lot of examples that use xmlns:dcterms="http://purl.org/dc/terms/" or xmlns:sioc="http://rdfs.org/sioc/ns#" then there is this video that uses FOAF vocabulary.
This is all pretty confusing and I am not sure what these vocabularies mean or what is best to use for the data I am describing. Is there some trick I am missing?
There are many vocabularies. And you could create your own, too, of course (but you probably shouldn’t before you checked possible alternatives).
You’d have to look for vocabularies for your specific needs, for example
by browsing and searching on http://lov.okfn.org/dataset/lov/ (they collect and index open vocabularies),
on W3C’s RDFa Core Initial Context (it lists vocabularies that have pre-defined prefixes for use with RDFa), or
by browsing through http://prefix.cc/ (it’s a lookup for typically used namespaces, but you might get an overview by that).
After some time you get to know the big/broad ones: Schema.org, Dublin Core, FOAF, RSS, SKOS, SIOC, vCard, DOAP, Open Graph, Ontology for Media Resources, GoodRelations, DBpedia Ontology, ….
The simplest thing is to check if schema.org covers your needs. Schema.org is backed by Google and the other major search engines and generally pretty awesome.
If it doesn't suit your needs, then enter a few of the terms you need into a vocabulary search engine. My recommendation is LOV.
Another option is to just ask the community about the best vocabularies for the specific domain you need to represent. A good place is answers.semanticweb.com, which is like StackOverflow but with more RDF experts hanging out.
Things have changed quite a bit since that video was posted. First, like Richard said, you should check if schema.org fits your needs. Personally when I need to describe something that's not covered on schema.org, I check LOV as well. If, and only if I can't find anything in LOV, I will then consider creating a new type or property. A quick way to do this is to use http://open.vocab.org/
A newer version of RDFa was published since that video was released: RDFa 1.1 and RDFa Lite. If you want to use schema.org only, I'd recommend to check http://www.w3.org/TR/rdfa-lite/
Vocabularies are usually domain specific. The xmlns line is deprecated. The RDFa profile at http://www.w3.org/profile/rdfa-1.1 lists the vocabularies available as part of initial context. Sometimes vocabularies may overlap in the context of your data. Analogous to solving math prb by either Algebraic or Geometric or other technique, mixing up vocabularies is fine. Equal terms can be found using http://sameas.org/ For addressing your consumer base's favoritism amongst vocab recognition, skos:closeMatch and skos:exactMatch may be used, eg. "gr:Brand skos:closeMatch owl:Thing" with any terms you please. Prefix attribute can be used with vocabularies besides those covered by initial context like: prefix="fb: http://ogp.me/ns/fb# vocab2: path2 ..." For cross-cutting concern across different domain vocabularies such as customizing presentation in search results microdata using schema.org guidelines should be beneficial. However, as this has nothing to do with specialization in any peculiar domain, prefixes are unavailable in this syntax. RDFa vocab have been helpful in such specific domain contexts that content seems to appeal further to participative audience while microdata targets those who've lost their way. For tasks that are too simple to merit full-fledged vocab, but have semantic implications, try http://microformats.org/ Interchanging usage of REST profile URIs for vocabs amongst the 3 syntaxes is valid, but useless owing to lack of affordable manpower to implement alternative support for the vocabs on the Web scale. How & why schema.org vocab merited separate microdata syntax of its own is discussed by Google employee Ian Hickson a. k. a. Hixie- the editor of WHATWG HTML5 draft at http://logbot.glob.com.au/?c=freenode%23whatwg&s=28+Nov+2012&e=28+Nov+2012#c747855 or http://krijnhoetmer.nl/irc-logs/whatwg/20121128#l-1122 If only Google had smart enough employees to implement parser for 1 syntax whose WG included its own employee also, then RDFa Lite inside RDFa would have been another course like Core Java within Java, & no need of separate microdata named mocking rip-off, but alas- our's is an imperfect world!
I am building an ontology-processing tool and need lots of examples of various owl ontologies, as people are building and using them in the real world. I'm not talking about foundational ontologies such as Cyc, I'm talking about smaller, domain-specific ones.
There's no definitive collection afaik, but these links all have useful collections of OWL and RDFS ontologies:
schemaweb.info
vocab.org
owlseek
linking open data constellation
RDF schema registry (rather old now)
In addition, there are some general-purpose RDF/RDFS/OWL search engines you may find helpful:
sindice
swoogle
Ian
My go-to site for this probably didn't exist at the time of the question. For latecomers like me:
Linked Open Vocabularies
I wish I'd found it much sooner!
It's well-groomed, maintained, has all the most-popular ontologies, and has a good search engine. However, it doesn't include some specialized collections, most notably, (most of?) the stuff in OBO Foundry.
Thanks! A couple more I found:
OntoSelect - browsable ontology repository
Protege Ontology Library
CO-ODE Ontologies
Within the life-science domain, the publically abvailable ontologies can be found listed on the OBO Foundry site. These ontologies can be queried via the ontology lookup service or the NCBO's Bioportal, which also contains additional resources.
One more concept search tool: falcons
There is also one good web engine for searching for ontologies. It is called Watson Semantic Web Search and you can try it here.