Simon Whatley » FOAF

An Introduction to the Semantic Web

Simon — Fri, 18 Jun 2010 12:20:49 +0000

The Semantic Web is a web of data. There is lots of data we all use every day, and most of it is not part of the web. I can see my bank statements on the web, and my photographs, and I can see my appointments in a calendar. But can I see my photos in a calendar to see what I was doing when I took them and on a map so I know where I took them? Can I see bank statement lines in a calendar? The answer, right now, is no.

But why not? Because we don’t have a web of data. Because data is controlled by applications, and each application keeps its data to itself; applications don’t like to share.

The original Web mainly concentrated on the interchange of documents, however, the Semantic Web is about two things: It is about common formats for integration and combination of data drawn from diverse sources. It is also about language for recording how the data relates to real world objects. That allows a person, or a machine, to start off in one database, and then move through an unending set of databases which are connected not by wires but by being about the same thing.

Tim Berners-Lee describes the Semantic Web vision as:

I have a dream for the Web [in which computers] become capable of analysing all the data on the Web, the content, links, and transactions between people and computers. A Semantic Web, which should make this possible, has yet to emerge, but when it does, the day-to-day mechanisms of trade, bureaucracy and our daily lives will be handled by machines talking to machines. The intelligent agents people have touted for ages will finally materialise.

What are the ideas and technologies that facilitate this vision? Below I give an overview and links to a number of them:

Linked Data

Linked Data is about using the Web to connect related data that wasn’t previously linked, or using the Web to lower the barriers to linking data currently linked using other methods. More specifically, Wikipedia defines Linked Data as “a term used to describe a recommended best practice for exposing, sharing, and connecting pieces of data, information, and knowledge on the Semantic Web using URIs and RDF.”

Resource Description Framework

The Resource Description Framework (RDF) is a general-purpose language for representing information in the Web.

The Resource Description Framework Schema (RDF-S) is a semantic extension of RDF that provides mechanisms for describing groups of related resources and the relationships between these resources.

The Resource Description Framework in Attributes (RDFa) allows authors to add meaning to web page elements. Using a few simple XHTML attributes, authors can mark up human-readable data with machine-readable indicators for browsers and other programs to interpret. A web page can include markup for items as simple as the title of an article, or as complex as a user’s complete social network.

Friend of a Friend (FOAF)

The Friend of a Friend project is creating a Web of machine-readable pages describing people, the links between them and the things they create and do. FOAF is about your place in the Web, and the Web’s place in our world. FOAF is a simple technology that makes it easier to share and use information about people and their activities (eg. photos, calendars, weblogs), to transfer information between Web sites, and to automatically extend, merge and re-use it online.

Web Ontology Language (OWL)

The OWL Web Ontology Language is designed for use by applications that need to process the content of information instead of just presenting information to humans. OWL facilitates greater machine interpretability of Web content than that supported by XML, RDF, and RDF Schema (RDF-S) by providing additional vocabulary along with a formal semantics.

Dublin Core Metadata Initiative (DCMI)

The Dublin Core set of metadata elements provides a small and fundamental group of text elements through which most resources can be described and catalogued. Using only 15 base text fields, a Dublin Core metadata record can describe physical resources such as books, digital materials such as video, sound, image, or text files, and composite media like web pages. Metadata records based on Dublin Core are intended to be used for cross-domain information resource description and have become standard in the fields of library science and computer science. Implementations of Dublin Core typically make use of XML and are Resource Description Framework (RDF) based.

Triplestore

A triplestore is a purpose-built database for the storage and retrieval of Resource Description Framework (RDF) metadata.

Much like a relational database, information is stored in a triplestore and retrieved via a query language called SPARQL. Unlike a relational database, a triplestore is optimised for the storage and retrieval of many short statements called triples, in the form of subject-predicate-object, like “Bob is 35″ or “Bob knows Fred”.

http://en.wikipedia.org/wiki/Triplestore

SPARQL Protocol and RDF Query Language (SPARQL)

SPARQL is an RDF query language, which can be used to express queries across diverse data sources, whether the data is stored natively as RDF or viewed as RDF via middleware. SPARQL contains capabilities for querying required and optional graph patterns along with their conjunctions and disjunctions. SPARQL also supports extensible value testing and constraining queries by source RDF graph. The results of SPARQL queries can be results sets or RDF graphs.

Simple Knowledge Organization System (SKOS)

SKOS is a family of formal languages designed for representation of thesauri, classification schemes, taxonomies, subject-heading systems, or any other type of structured controlled vocabulary. SKOS is built upon RDF and RDF-S, and its main objective is to enable easy publication of controlled structured vocabularies for the Semantic Web.

Persistent Uniform Resource Locator (PURL)

A PURL is a type of Uniform Resource Locator (URL) that does not directly describe the location of the resource to be retrieved but instead describes an intermediate, more persistent location which, when retrieved, results in redirection (e.g. via a 302 HTTP status code) to the current location of the final resource.

PURLs are an interim measure, while Uniform Resource Names (URNs) are being mainstreamed, to solve the problem of transitory URIs in location-based URI schemes like HTTP.

Thomson Reuters OpenCalais

OpenCalais is a rapidly growing toolkit of capabilities that allow you to readily incorporate state-of-the-art semantic functionality within your blog, content management system, website or application.

The OpenCalais Web Service automatically creates rich semantic metadata for the content you submit. Using Natural Language Processing (NLP), machine learning and other methods, Calais analyses your document and finds the entities within it. Calais goes beyond classic entity identification returning the facts and events hidden within your text as well.

http://www.opencalais.com

If you have any more suggestions that should be included above, I’ll be happy to hear them.

Data Portability for Social Networks

Simon — Fri, 28 Mar 2008 09:50:11 +0000

Social network portability is one of several user-interface ideas and suggestions in the area of data-portability. As users, our identity, photos, videos and other forms of personal data should be discoverable by, and shared between our chosen (and trusted) tools or vendors. When you join a new site, you should be able to import or preferably subscribe to your profile information and your social network from any existing profile of yours. We need a DHCP for Identity. A distributed File System for data. The technologies already exist, we simply need a complete reference design to put the pieces together. This problem is solved by a number existing technologies and initiatives: Microformats, OpenID, OAuth, RDF, RSS, OPML and APML.

Data Portabilities mission is to put all existing technologies and initiatives in context to create a reference design for end-to-end Data Portability. To promote that design to the developer, vendor and end-user community.

This post serves a brief primer to each of these technologies.

Microformats

Designed for humans first and machines second, microformats are a set of simple, open data formats built upon existing and widely adopted standards. Instead of throwing away what works today, microformats intend to solve simpler problems first by adapting to current behaviours and usage patterns (e.g. XHTML, blogging).

Examples include:

People and Organizations: hCard
Calendars and Events: hCalendar
Opinions, Ratings and Reviews: VoteLinks, hReview
Social Networks: XFN
Licenses:: rel-license
Tags, Keywords, Categories: rel-tag
Lists and Outlines: XOXO

If you use Flickr, Technorati, Upcoming, Last.fm, Twitter, Cork’d or any number of other services, you can conceivably share data between the different services providers automatically.

More details can be found on the microformats website.

OpenID

OpenID is an open, decentralized framework for user-centric digital identity. OpenID takes advantage of already existing internet technology (URI, HTTP, SSL, Diffie-Hellman) and realizes that people are already creating identities for themselves whether it be at their blog, photostream, profile page, etc. With OpenID you can easily transform one of these existing URIs into an account which can be used at sites which support OpenID logins.

In other words, OpenID allows users to login using shared credentials across different services. It also allows users to decide what information to share between services. For example, you can allow the use of your address on one service, but not another. You can think of OpenID as an extension to the single sign on used by Google or Yahoo! to access their various services.

More details can be found on the OpenID website.

OAuth

The OAuth protocol is less about authentication, which is the realm of OpenID, but rather authorisation. OAuth is an open protocol to allow secure API authorisation in a simple and standard method from desktop and web applications. For consumer developers, OAuth is a method to publish and interact with protected data. For Service Provider developers, OAuth gives users access to their data while protecting their account credentials.

A number of services have already been implemented. These include Fire Eagle, Open Social, Pownce, Get Satisfaction and Magnolia.

More details can be found on the OAuth website.

Resource Description Framework (RDF)

RDF is a family of World Wide Web Consortium (W3C) specifications originally designed as a metadata model but which has come to be used as a general method of modeling information, through a variety of syntax formats.

The RDF metadata model is based upon the idea of making statements about resources in the form of subject-predicate-object expressions, called triples in RDF terminology. The subject denotes the resource, and the predicate denotes traits or aspects of the resource and expresses a relationship between the subject and the object. For example, one way to represent the notion “The sky has the color blue” in RDF is as the triple: a subject denoting “the sky”, a predicate denoting “has the color”, and an object denoting “blue”. RDF is an abstract model with several serialization formats (i.e. file formats), and so the particular way in which a resource or triple is encoded varies from format to format.

This mechanism for describing resources is a major component in what is proposed by the W3C‘s Semantic Web activity: an evolutionary stage of the World Wide Web in which automated software can store, exchange, and use machine-readable information distributed throughout the web, in turn enabling users to deal with the information with greater efficiency and certainty. RDF‘s simple data model and ability to model disparate, abstract concepts has also led to its increasing use in knowledge management applications unrelated to Semantic Web activity.

More details can be found on the W3C website.

Really Simple Syndication (RSS)

RSS is a family of Web feed formats used to publish frequently updated content including, but not limited to, blog entries, news headlines, and podcasts. An RSS document, which is called a “feed” or “web feed” or “channel”, contains either a summary of content from an associated web site or the full text. RSS makes it possible for people to keep up with web sites in an automated manner that can be piped into special programs or filtered displays.

RSS content can be read using software called an “RSS reader”, “feed reader” or an “aggregator”. The user subscribes to a feed by entering the feed’s link into the reader or by clicking an RSS icon in a browser that initiates the subscription process. The reader checks the user’s subscribed feeds regularly for new content, downloading any updates that it finds.

More details can be found on the RSS Board website.

Outline Processor Mark-up Language (OPML)

OPML is an XML format for outlines. Originally developed by Radio UserLand as a native file format for an outliner application, it has since been adopted for other uses, the most common being to exchange lists of web feeds between web feed aggregators.

The OPML specification defines an outline as a hierarchical, ordered list of arbitrary elements. The specification is fairly open which makes it suitable for many types of list data.

More details can be found on the OPML website.

Attention Profiling Mark-up Language (APML)

APML allows you to share your own personal Attention Profile in much the same way that OPML allows the exchange of reading lists between News Readers. The idea is to compress all forms of Attention Data into a portable file format containing a description of your ranked interests.

Services that have adopted APML include Bloglines, Cluztr, Dandelife, Engagd, Idiomag, OpenLink Data Spaces and Particls.

More details can be found on the APML website.

Securely transfering personal data around the web has become an increasingly important concept to not only users of the web, but service providers. Both Plaxo and Six Apart have been working on a system to allow the transferral of data. However, since Google announce Open Social and the Open Social API, the mantle has been handed over and there is now a strong commitment to realising data portability.