Content-type: text/html ~ Stephen's Web ~ Semantic Networks and Social Networks

Stephen Downes

Knowledge, Learning, Community

Oct 10, 2005

This Journal Article published as Semantic Networks and Social Networks in The Learning Organization Journal Volume 12, Number 5 411-417 May 01, 2005. Emerald Group Publishing Limited [Link] [Info] [List all Publications]

The Learning Organization Journal, 12(5).


Purpose: To illustrate the need for social network metadata within semantic metadata.

Design/methodology/approach: Surveys properties of social networks and the semantic web, suggests that social network analysis applies to semantic content, argues that semantic content is more searchable if social network metadata is merged with semantic web metadata.

Findings: The use of social network metadata will alter semantical searches from being random with respect to source to direct with respect to source, which will increase the accuracy of search results.

Research limitations/implications: Suggests that existing XML schemas for semantic web content be modified.

Practical implications: Introduction and overview of a new issue.

Originality/value: Foundational to the concept of the semantic social network; will be useful as an introduction to future work.

Keywords: Information networks, Internet, Social networks

Paper type: Conceptual paper

Semantic Networks and Social Networks

A social network is a collection of individuals linked together by a set of relations. In discussions of social networks the individuals in question are usually humans, though work in social network theory has found similarities between communities of humans and, say, communities of crickets (Buchanan, 2002, p. 49) or members of a food web (Buchanan, 2002, p. 17). Entities in a network are called "nodes" and the connections between them are called "ties" (Cook, 2001). Ties between nodes may be represented as matrices, and the properties of these networks therefore studied as a subset of graph theory (Garton et al., 1997).

A key property of social networks is that nodes that might be thought of as widely distant from each other - a farmer in India, say, and the President of the United States - may actually be much more closely connected that otherwise imagined. This phenomenon, sometimes known as "six degrees", was measured (Milgram, 1967) and, as the name suggests, no more than six steps were required to connect any two people in the United States (Buchanan, 2002, p. 25). With the arrival of the internet as a global communications network ties between individuals became both much easier to create and much easier to measure.

Social networking web sites fostering the development of explicit ties between individuals as "friends" began to appear in 2002. Sites such as Friendster, Tribe, Flickr the Facebook and LinkedIn were early examples. Less explicitly based on fostering relationships than, say, online dating sites, these sites nonetheless sought to develop networks or "social circles" of individuals of mutual interest. LinkedIn, for example, seeks to connect potential business partners or prospective employers with potential employers. Flickr connects people according to their mutual interest in photography. And numerous sites offer dating or matchmaking services. After an initial surge of interest, however, social networking sites have tended to stagnate (Aquino, 2005). It is arguable that social networking, by itself, has limited practical use.

The semantic web, as originally conceived by Tim Berners-Lee, "provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries" (W3C, 2001). Developed using the resource description framework, it consists of an interlocking set of statements (known as "triples"). "Information is given well-defined meaning, better enabling computers and people to work in cooperation" (Berners-Lee et al., 2001). The semantic web is therefore, a network of statements about resources.

In particular, RDF enables the creation of statements intended to describe different types of resources. The terms used in these statements are defined in schemas, themselves RDF documents, which list the terms to be used and (in some cases) the types of values allowed, and the relations between them. "Using RDF Schema, we can say that 'Fido' is a type of 'Dog', and that 'Dog' is a sub class of animal." Beyond schemas, ontologies enable complex representations of related entities and their descriptions.

Though applications of the semantic web in particular have thus far been limited, there have emerged since its introduction numerous projects characterizing and encoding descriptions of different types of resources in XML (Downes, 2003a). The majority of these projects seem to be centred around the classification of information and resources. For example, learning object metadata (LOM) describes learning resources. Dublin Core provides bibliographic information about resources. These resources are typically identified explicitly in the XML or RDF, typically using a uniform resource identifier (URI) based on its address on the world wide web, or via some other form of identifier system, such as digital object identifier (DOI).

Outside professional and academic circles, arguably the most widespread adoption of the semantic web has been in the use of RSS. RSS, known variously as rich site summary, RDF site summary or really simple syndication, was devised by Netscape in order to allow content publishers to syndicate their content, in the form of headlines and short introductory descriptions, on its My Netscape web site (Downes, 2000). The use of RSS has increased exponentially, and now RSS descriptions (or its closely related cousin, Atom) are used to summarize the contents of 100s of newspapers and journals, weblogs (including the roughly eight million weblogs hosted collectively by Blogger, Typepad, LiveJournal and Userland), wikis and more.

There are no doubt purists who deny that RSS is an instantiation of the semantic web. However, all RSS files are undeniably written in XML, and a type of RSS (specifically, RSS 1.0) is explicitly written in RDF (Beged-Dov, 2001a). At its core, RSS consists of some simple XML elements: a "channel" element defining the publication title, description and link; and a series of "item" elements defining individual resource titles, descriptions and links. Since, RSS 1.0, however, the RSS format has allowed these basic elements to be extended; the role of schemas is fulfilled by namespaces, and these namespaces define (sometimes implicitly) a non-core vocabulary. Such extensions (also known in RSS 1.0 as "modules") include Dublin Core, Creative Commons, Syndication and Taxonomy (Beged-Dov, 2001b).

Initiatives to represent information about people in RDF or XML have been fewer and demonstrably much less widely used. The HR-XML (Human Resources XML) Consortium has developed a library of schemas "define the data elements for particular HR transactions, as well as options and constraints governing the use of those elements" (HR-XML Consortium, 2005). Customer Information Quality TC, an OASIS specification, remains in formative stages (OASIS, 2005). And the IMS learner information package specification restricts itself to educational use (IMS, 2005). It is probably safe to say that there is no commonly accepted and widely used specification for the description of people and personal information. As suggested above, developments in the semantic web have addressed themselves almost entirely to the description of resources, and in particular, documents.

Outside the professional and academic circles, there have been efforts to represent the relations between persons found in social networks explicitly in XML and RDF. Probably the best known of these is the Friend of a Friend (FOAF) specification (Dumbill, 2002). Explicitly RDF, a FOAF description will include data elements for personal information, such as one's name, e-mail address, web site, and even one's nearest airport. FOAF also allows a person to list in the same document a set of "friends" to whom the individual feels connected. A similar initiative is the XHTML Friends Network (XFN) (GPMG, 2003). XFM involves the use of "rel" attributes within links contained in a blogroll (a "blogroll" is a list of web sites the owner of a blog will post to indicate readership).

Though FOAF and XFN have obtained some currency, it is arguable that they have declined to the same sort of stagnation that has befallen social network web sites. While many people have created FOAF files, for example, few applications (and arguably no useful applications) have been developed for FOAF. And while some useful extensions to FOAF have been proposed (such as a trust metric, PGP public key, and default licensing scheme), these have not been adopted by the community at all.

Perhaps, given the demonstrable lack of enduring interest in social network systems, either site-based, as in LinkedIn? and Orkut, or semantic web-based, as in FOAF or XFN, it could be argued that there is no genuine need for a social network system (beyond, perhaps, matching and dating sites). Perhaps, as some have argued, such systems, once they get too large to be manageable, simply collapse in on themselves, their users suffocated under the weight of millions of enquiries and advertising messages, as happened to e-mail, Usenet and IRC (Cervini, 2003).

But the evidence seems to weigh against this supposition. Certainly, the management of personal information has long been touted as necessary for authentication. Authentication - i.e. a mechanism of proving that a person is who they say they are - is used to control access to restricted information. Projects such as Microsoft s Passport and the liberty alliance have for years attempted to promote a common authentication scheme. Sites such as LiveJournal and Blogger have begun to require login access in order to submit comments, as a means of discouraging spam. Newspapers, online journals and online communities typically require some sort of login process. Projects such as SxIP and light-weight identity (LID) http://lid.netmesh. org/ have attempted to create a single sign-on solution for logins. So there is a need for personal descriptions, at least to control access.

We could perhaps leave descriptions of identity as something for individual sites to work out were there not wider issues pertaining to the semantic web that also require at least some element of personal identity to address. To put the problem briefly: so long as descriptions of resources are based solely on the content of those resources then users of the semantic web will be hampered in their efforts to learn about new resources outside the domain of their own expertise. The reason for this is what might be called the "dictionary principle" - in order to find a resource, the searcher must already know about the topic domain they are searching through, since resources are defined in terms specific to that domain (in other words if you want to find a word in a dictionary, you have to already know how to spell it).

In fact, what has tended to happen in the largest current implementation of the semantic web, the network of RSS resources, is that searchers have, within certain parameters, tended to seek out resources randomly. They type in a search term in Google, for example, without any foreknowledge of where the resource they are seeking will turn up. They tend to link to sources they find in this manner; thus, the network of connections between resources (expressed in RSS, as on web sites, as links) manifests itself as a random network.

The proof of this is found in the studies of social networks discussed at the beginning of this paper. The links found in web pages are instances of what are known as "weak ties". Weak ties are are acquaintances who are not part of your closest social circle, and as such have the power to act as a bridge between your social cluster and someone else's (Cervini, 2003). Weak ties created at random in this way lead to what Gladwell called "supernodes" individuals with many more ties than other resources. (Gladwell, in other words, some sites get most of the links, while most others get many fewer links. "A power-law distribution basically indicates that 80 per cent of the traffic is going to 1 per cent of the participants in the network." (Barabasi, 2002; Cervini, 2003).

Numerous commentators, from Barabasi forward, have made the observation that power laws occur naturally in random networks, and some pundits, such as Clay Shirky, have shown that the distribution of visitors to web sites and links to web sites follow a power law distribution (Shirky, 2003). Our purpose here is to take the inference in the opposite direction: because readership and linkage to online resources exhibits a power law distribution, it follows that these resources are being accessed randomly. Therefore, despite the existence of a semantic description of these resources, readers are unable to locate them except via the location of an individual - a super connector - likely to point to such resources.

It is reasonable to assume that a less random search would result in more reliable results. For example, as matters currently stand, were I to conduct a search for "social networking" then probability dictates that I would most likely land on Clay Shirkey, since Shirky is a super-connector and therefore cited in most places I am likely to find through a random search. But Shirky s politician affiliation and economic outlook may be very different from mine; it would be preferable to find a resource authored by someone who shares my own perspective more closely. Therefore, it is reasonable to suppose that if I were to search for a resource based on both the properties of the resource and the properties of the author, I would be more likely to find a resource than were I to search for a random author.

Such a search, however, is impossible unless the properties of the author are available in some form (presumably, something like an RDF file), and also importantly, that the properties of the author are connected in an unambiguous way to the resources being sought.

I have proposed (Downes, 2004) that social networking be combined explicitly with the semantic web in what I have called the semantic social network (SSN). Essentially, SSN involves two major components: first, that there be, expressed in XML or RDF, descriptions of persons (authors, readers, critics) publicly available on the web, sometimes with explicit ties to other persons; and second, that references to these descriptions be employed in RDF or XML files describing resources.

Neither would at first glance seem controversial, but as I mention above, there is little in the way of personal description in the semantic web, and even more surprisingly, the vast majority of XML and RDF specifications identify persons (authors, editors, and the like) with a string rather than with a reference to a resource. And such strings are ambiguous; such strings do not uniquely identify a person (after all, how many people named John Smith are there?) and they do not identify a location where more information may be found (with the result that many specifications require that additional information be contained in the resource description, resulting in, for example, the embedding of VCard information in LOM files).

It should be immediately obvious that the explicit conjunction of personal information and resource information within the context of a single distributed search system will facilitate much more fine-grained searches than either system considered separately. For example, were I look for a resource on social networks , I may request resources about social networks authored by people who are similar to me , where similarity is defined as a mapping of commonalities of personal feature sets: language and nationality, say, commonly identified friends , or even similarities in licensing preferences. Or, were I to (randomly or otherwise) locate an individual with, to me, an interesting point of view, I could "search for all articles written by n and friends of n".

Identity plays a key role in projected future developments of the semantic web. In his famous architecture diagram , Tim Berners-Lee identifies a digital signature as being the backbone of RDF, ontology, logic and proof (Berners-Lee, 2000). A digital signature establishes what he calls the provenance of a statement: we are able to determine not only that "A is a B", but also according to whom A is a B. "Digital signatures can be used to establish the provenance not only of data but also of ontologies and of deductions." (Dumbill, 2000). But as useful as a digital signature may be for authentication, a digital signature is an unfaceted identification. To know something about the person making the assertion, it will be necessary to attach a personal identity to an XML or RDF description.

As we examine the role that personal identity plays in semantic description, it becomes apparent that much more fine-grained descriptions of resources themselves become possible. For there are three major ways in which a person may be related to a resource: as the author or creator of the resource; as the user or consumer of the resource; and as a commentator or evaluator of the resource. Each of these three types of person may create metadata about a resource. An author may give a resource a title, for example. A user may give the resource a "hit" or a reference (or a "link"). And a commentator may provide an assessment, such as "good" or "board certified". Metadata created by these three types of persons may be called "first party metadata", "second party metadata" and "third party metadata", respectively (Downes, 2003b).

The semantic web and social networking have each developed separately. But the discussion in this short paper should be sufficient to have shown that they need each other. In order for social networks to be relevant, they need to be about something. And in order for the semantic web to be relevant, it needs to be what somebody is talking about. Authors need content, and content needs authors.


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Further reading

Gladwell, M. (2000), The Tipping Point: How Little Things Can Make a Big Difference, Little, Brown & Company, Boston, MA, pp. 45-6.

Palmer, S.B. (2001), The Semantic Web: An Introduction, available at:

Vitiello, E. (2002), FOAF, available at:

Stephen Downes Stephen Downes, Casselman, Canada

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