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Friend of Friend(FOAF)

(2011-09-22 09:08:21)






分类: 语义网

1Friend of Friend(FOAF)


The basic idea behind FOAF is simple: the Web is all about making connections between things. FOAF provides some basic machinery to help us tell the Web about the connections between the things that matter to us.


Thousands of people already do this on the Web by describing themselves and their lives on their home page. Using FOAF, you can help machines understand your home page, and through doing so, learn about the relationships that connect people, places and things described on the Web. FOAF uses W3C's RDFtechnology to integrate information from your home page with that of your friends, and the friends of your friends, and their friends



We want a better way of keeping track of the scattered fragments of data currently represented in the Web.


We want to be able to find documents in the Web based on their properties and inter-relationships; we want to be able to find information about people based on their publications, employment details, group membership and declared interests. We want to be able to share annotations, ratings, bookmarks and arbitrary useful data fragments using some common infrastructure. We want a Web search system that's more like a database and less like a lucky dip. We need it to be be distributed, decentralised, and content-neutral.


FOAF, if successful, should help the Web do the sorts of things that are currently the proprietary offering of centralised services.


RDF seems to offer a lot of promise in this area. While RDF is defined in terms of a rather abstract information model, our needs are rather practical. We want to be able to ask the Web sensible questions and common kinds of thing (documents, organisations, people) and get back sensible results.


"Find me today's web page recommendations made by people who work for Medical organisations".


"Find me recent publications by people I've co-authored documents with."


"Show me critiques of this web page, and the home pages of the author of that critique"


3Saying things in RDF

At the heart of the RDF is an information model based around the idea of simple 3-part sentences such as "dan hometown-name bristol", or "martin homepage-url http://weird.co.uk/". It turns out that this somewhat stilted way of describing things can be very expressive, since RDF allows anyone to define new terms such as 'homepage', 'hometown', 'bestFriendHomepage' and so on. The FOAF starter vocabulary provides some basic terms such as these to provide a common language for machine-readable homepages. RDF allows multiple such languages to be mixed together - for example, you can use the "Dublin Core" vocabulary to describe documents you've written or contributed to.

RDF的核心是一个信息模型,它的思想是将一个句子分成三部分,例如“dan hometown-name bristol”,"dan hometown-name bristol""martin homepage-url http://weird.co.uk/"等,显然这种描述事物的方法显得有点呆板而且代价较高,因为RDF允许任何人定义新的术语,例如'homepage', 'hometown', 'bestFriendHomepage'等等。FOAFstarter vocabulary提供了一些基本的词汇,例如那些提供为机器可读主页提供通用语言的词汇。RDF允许多种这样的语言混合使用,比如,你可以使用Dublin Core的词汇来描述你写作的文档。

The FOAF system itself doesn't care much about what you say, but about the way in which you say it. By using a carefully designed file format and a simple common information model, we can build a distributed database in which anyone can say anything about anything


By squashing our information into the simple 3-part-sentence framework, we can build systems that automatically combines such data from multiple sources.


4Starter Vocabulary (updated in 2008)

The starter vocabulary for FOAF combines some basic RDF vocabulary we invented for the project, plus other useful existing vocabulary such as the Dublin Core metadata elements. The Friend of a Friend (FOAF) vocabulary provides the basics. This XML namespace defines RDF properties useful for FOAF applications.

FOAFstarter vocabulary结合了我们自己为FOAF项目发明的一些基本RDF词汇,并且添加了其他现存的有用的词汇表,如Dublin Core元数据元素。FOAF词汇表只提供一些基本的词汇。XML命名空间定义了对FOAF应用有用的RDF属性。

In the original project, this was flagged as "version 0.1" to indicate it as a work-in-progress. The vocabulary has grown substantially since then, but we have made the choice to evolve it "in place", adding items into a growing dictionary of terms whose formal identifier remains 'http://xmlns.com/foaf/0.1/'. Today, the '0.1' is best thought of as '1.0' approached backwards. We version FOAF's terms individually, and mark each as 'stable', 'unstable' or 'testing' to provide a hint to implementors. This design allows us to avoid costly versioning problems, and for the specification to be gradually improved without causing a needless proliferation of vocabulary version identifiers.

在项目的初期,"version 0.1"表明FOAF还只是个半成品。词汇表正是从那时开始增长的,但是我们选择了在适当的地方改进了该词汇表,向增长的术语字典中增加了一些词汇,但他们的正是形式标识符仍然是'http://xmlns.com/foaf/0.1/',现在FOAF发展到了"version 1.0",我们自己定制FOAF词汇的版本,并将其用'stable', 'unstable' 或者 'testing'来标识,以显示其实现的层次,这样可以解决版本问题。



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