What is the Semantic Web?

“The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation.” 语义网是当前网络的延伸，在这种网络中，信息被赋予了明确的含义，更好地使计算机和人们能够合作工作
T. Berners-Lee, J. Hendler, O. Lassila, “The Semantic Web”, Scientific American, May 2001
By 2009 “linked data” had become the “application of the Semantic Web”. Linked data infrastructures are being widely rolled out, including across the Australian Government. Since around 2015, largely driven by Google, “knowledge graphs” have become the application that is driving research and industrial uptake of semantic web technologies.
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What is Linked Open data?

•Web of data where web content is processed by machines, without direct human readers, but not a separate Web. 由机器处理网络内容的数据网络，没有直接的人类阅读器，但不是一个独立的网络。
•The web as a huge, dynamic, evolving database of facts, rather than pages, that can be interpreted and presented in many ways (mashups).
•Fundamental importance of ontologies to describe the fact that represents the data. 本体对于描述代表数据的事实的根本重要性。
•Where is the “semantics”?
–RDF(S) emphasises labelled links as the source of meaning: essentially a graph model either stored locally in a triple store or distributed as linked open data. A label (that is a URI) uniquely identifies a concept and reuse of the label implies the same meaning.RDF(S)强调标记链接是意义的来源:本质上是一个图形模型，要么存储在本地的三重存储中，要么作为链接的开放数据分发。标签(即URI)唯一标识一个概念，重复使用标签意味着相同的含义。
–OWL adds emphasis on inference as the source of meaning: a label also refers to a package of logical axioms with a proof theory over a model-theoretic semantics. OWL强调推理是意义的来源:标签也指一组逻辑公理，其证明理论优于模型理论语义。
–Mostly, the two notions of meaning coincide. 大多数情况下，这两个意义概念是一致的。

What do we need to build it?

  1. Identity
  • so things can be referred to
  1. Relationships
  • so things can be connected to/ described by other things. This is where the notion of a _graph _comes from. 因此事物可以与其他事物联系起来/用其他事物来描述。这就是图形概念的来源。
  1. Inference
  • so general statements about things can be applied to particular things and don’t need to be restated every time. This is how _knowledge _arises.
  1. A way of encoding all this
  • serialisation in RDF 1.1: Turtle, RDF/XML, N-Triples, N-Quads, TriG, JSON-LD

And the Open World Assumption. All information to hand is always assumed to be only partial, i.e. from the absence of a statement alone, a deductive reasoner cannot (and must not) infer that the statement is false. Beware, this is very different to the logic of relational databases.
开放世界假设。手头上的所有信息总是被假定为只是部分的，也就是说，仅从没有一个陈述，演绎推理者不能(也绝不能)推断该陈述是错误的。请注意，这与关系数据库的逻辑非常不同。