Archive for the ‘Virtuoso’ Category

Linked Data and the SOA Software Development Process

Thursday, November 17th, 2011

We have quite a rigorous SOA software development process however the full value of the collected information is not being realized because the artifacts are stored in disconnected information silos. So far attempts to introduce tools which could improve the situation (e.g. zAgile Teamwork and Semantic Media Wiki) have been unsuccessful, possibly because the value of a Linked Data approach is not yet fully appreciated.

To provide an example Linked Data view of the SOA services and their associated artifacts I created a prototype consisting of  Sesame running on a Tomcat server with Pubby providing the Linked Data view via the Sesame SPARQL end point. TopBraid was connected directly to the Sesame native store (configured via the Sesame Workbench) to create a subset of services sufficient to demonstrate the value of publishing information as Linked Data. In particular the prototype showed how easy it became to navigate from the requirements for a SOA service through to details of its implementation.

The  prototype also highlighted that auto generation of the RDF graph (the data providing the Linked Data view) from the actual source artifacts would be preferable to manual entry, especially if this could be transparently integrated with the current software development process. This is has become the focus of the next step, automated knowledge extraction from the source artifacts.

Artifacts

Key artifact types of our process include:

A Graph of Concepts and Instances

There is a rich graph of relationships linking the things described in the artifacts listed above. For example the business entities defined in the UML analysis model are the subject of the service and service operations defined in the Service Contracts. The service and service operations are mapped to the WSDLs which utilize the Xml Schema’s that provide an XML view of business entities. The JAX-WS implementations are linked to the WSDLs and Xml Schema’s and deployed to the Oracle Weblogic Application Server where the configuration files list the external dependencies. The log files and defects link back to specific parts of the code base (Subversion revisions) within the context of specific service operations. The people associated with the different artifacts can often be determined from artifact meta-data.

RDF, OWL and Linked Data are a natural fit for modelling and viewing this graph since there is a mix of concepts plus a lot of instances, many of whom already have a HTTP representation. Also the graph contains a number of transitive relationships , (for example a WSDL may import an Xml Schema which in turn imports another Xml Schema etc …) promoting the use of the owl:TransitiveProperty to help obtain a full picture of all the dependencies a component may have.

Knowledge Extraction

Another advantage of the RDF, OWL, Linked Data approach is the utilization of unique URIs for identifying concepts and instances. This allows information contain in one artifact, e.g. a WSDL, to be extracted as RDF triples which would later be combined with the RDF triples extracted from the JAX-WS annotation of Java source code. The combined RDF triples tell us more about the WSDL and its Java implementation than could be derived from just one of the artifacts.

We have made some progress with knowledge extraction but this is still definitely a work in progress. Sites such as ConverterToRdf, RDFizers and the Virtuoso Sponger provide tools and information on generating RDF from different artifact types. Part of the current experimentation is around finding tools that can be transparently layered over the top of the current software development process. Finding the best way to extract the full set of desired RDF triples from Microsoft Word documents is also proving problematic since some natural language processing is required.

Tools currently being evaluated include:

The Benefits of Linked Data

The prototype showed the benefits of Linked Data for navigating from the requirements for a SOA service through to details of its implementation. Looking at all the information that could be extracted leads on to a broader view of the benefits Linked Data would bring to the SOA software development process.

One specific use being planned is the creation of a Service Registry application providing the following functionality:

  • Linking the services to the implementations running in a given environment, e.g. dev, test and production. This includes linking the specific versions of the requirement, design or implementation artifacts and detailing the runtime dependencies of each service implementation.
  • Listing the consumers of each service and providing summary statistics on the performance, e.g. daily usage figures derived from audit logs.
  • Providing a list of who to contact when a service is not available. This includes notifying consumers of a service outage and also contacting providers if a service is being affected by an external component being offline, e.g. a database or an external web service.
  • Search of the services by different criteria, e.g. business entity
  • Tracking the evolution of services and being able to assist with refactoring, e.g answering questions such as “Are there older versions of the Xml Schemas that can be deprecated?”
  • Simplify the running of a specific Soapui test case for a service operation in a given environment.
  • Provide the equivalent of a class lookup that includes all project classes plus all required infrastructure classes and returns information such as the jar file the class is contained in and JIRA and Subversion information.

DBpedia Examples using Linked Data and Sparql

Monday, August 11th, 2008

Using Wikipedia, the largest online encyclopedia, users can browse and perform full-text searches, but programmatic access to the knowledge-base is limited.

The DBpedia project extracts structured information from Wikipedia opening it up to programmatic access using Semantic Web technologies such as Linked Data and SPARQL. This means that the linking and reasoning abilities of RDF and OWL can be utilized and queries for specific information can be made using SPARQL.

Simplistically the mapping from the Wikipedia HTML based web pages to the DBpedia RDF based resources can be thought of as replacing “http://en.wikipedia.org/wiki/” with “http://dbpedia.org/resource/” but in reality there are some additional subtleties which are described in the article From Wikipedia URI-s to DBpedia URI.

The Wikipedia entry for “Civil Engineering” (http://en.wikipedia.org/wiki/Civil_Engineering) is used as an example to show how specific data can be retrieved from its DBpedia equivalent (http://dbpedia.org/resource/Civil_engineering).

When both the Wikipedia entry (http://en.wikipedia.org/wiki/Civil_Engineering) and its DBpedia equivalent (http://dbpedia.org/resource/Civil_engineering) are opened in a standard web browser they display similar information, however the DBpedia equivalent has been redirected to http://dbpedia.org/page/Civil_engineering.

This redirect can be viewed in Firefox using the Tamper Data Firefox Extension as shown in the image below.

Loading the DBpedia Resource

The initial status of 303 is the HTTP response code “303 See Other“. The server replied with the HTTP response code 303 in order to direct the browser to URI http://dbpedia.org/page/Civil_engineering which is a HTML page the browser can display. The original URI http://dbpedia.org/resource/Civil_engineering is an RDF resource that would not display as well in the HTML browser.

DBpedia implements a HTTP mechanism called content negotiation in order to provide clients such as web browsers with the information they request in a form they can display. The tutorial How to publish Linked Data on the Web describe this and other Linked Data techniques that are used by applications such as DBpedia.

In order to access the RDF resource directly a web client needs to tell the server to send it RDF data. A client can do this by sending the HTTP Request Header Accept: application/rdf+xml as part of its initial request. (The HTML browser had sent an Accept: text/html HTTP header indicating that it was requesting an HTML page.)

The Firefox Addon RESTTest can be used to set Accept: application/rdf+xml in the HTTP Request Header and directly request http://dbpedia.org/resource/Civil_engineering as shown in the image below.

In this case the request to http://dbpedia.org/resource/Civil_engineering succeeded as shown by the “Response Status 200″ and a RDF document was received as shown in the “Response Text”.

In both the RDF fragment shown in the image above and in the HTML page http://dbpedia.org/page/Civil_engineering the multiple language support is visible. The SPARQL queries below show how to extract specific information for a particular language.

SPARQL

DBpedia provides a public SPARQL endpoint at http://dbpedia.org/sparql which enables users to query the RDF datasource with SPARQL queries such as the following.

SELECT ?abstract
WHERE {
{ <http://dbpedia.org/resource/Civil_engineering> <http://dbpedia.org/ontology/abstract> ?abstract }
}

The query returns all the abstracts for Civil Engineering, in each of the available languages.

The next query refines the abstracts returned to just the language specified, in this case ‘en’ (English).

SELECT ?abstract
WHERE {
{ <http://dbpedia.org/resource/Civil_engineering> <http://dbpedia.org/ontology/abstract> ?abstract .
FILTER langMatches( lang(?abstract), ‘en’) }
}

The SNORQL query explorer shown in the image below, provides a simpler interface to the DBpedia SPARQL endpoint. The image below shows both the query and the result returned.

Other SPARQL endpoints such as http://demo.openlinksw.com/sparql/ (shown below) can query DBpedia by specifying the FROM NAMED clause to describe the RDF dataset. E.g.

SELECT ?abstract
FROM NAMED <http://dbpedia.org>
WHERE {
{ <http://dbpedia.org/resource/Civil_engineering> <http://dbpedia.org/ontology/abstract> ?abstract.
FILTER langMatches( lang(?abstract), ‘en’) }
}

Other Related DBpedia Articles

RDF as self-describing Data uses DBpedia and its SPARQL support to show how RDF is essentially ’self-describing’ – there is no need to know about traditional metadata (schemas) before exploring a data set.

Linking to DBpedia with TopBraid outlines the benefit of DBpedia in terms of providing relatively stable URIs for all relevant real-world concepts, thus making it a natural place to connect specific domain models with each other using the OWL built in propery owl:sameAs ( This property indicates that two URI references actually refer to the same thing ). TopBraid Composer provides support to link domain models with DBpedia .

Querying DBpedia provides examples of using SPARQL to query DBpedia.

Adding Semantic Markup to Your Rails Application with DBpedia and ActiveRDF and
Get Semantic with DBPedia and ActiveRDF describe using ActiveRDF to integrate DBpedia resources into web based applications. ActiveRDF is a library for accessing RDF data from Ruby and Ruby On Rails programs and can perform SPARQL queries.