science

Semantic Web Stack

Semantic Web Stack is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Semantic Web Stack rather than just read about it. In short: The Semantic Web Stack, also known as Semantic Web Cake or Semantic Web Layer Cake, illustrates the architecture of the Semantic Web. The Semantic Web is a collaborative movement led by international standards body the World Wide Web Consortium (W3C).

Key takeaways

Semantic Web Stack belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Semantic Web Stack to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Semantic Web Stack from memory before moving on to harder problems.

Reference excerpt

The Semantic Web Stack, also known as Semantic Web Cake or Semantic Web Layer Cake, illustrates the architecture of the Semantic Web. The Semantic Web is a collaborative movement led by international standards body the World Wide Web Consortium (W3C). The standard promotes common data formats on the World Wide Web. By encouraging the inclusion of semantic content in web pages, the Semantic Web aims at converting the current web, dominated by unstructured and semi-structured documents into a "web of data". The Semantic Web stack builds on the W3C's Resource Description Framework (RDF).

Overview The Semantic Web Stack is an illustration of the hierarchy of languages, where each layer exploits and uses capabilities of the layers below. It shows how technologies that are standardized for Semantic Web are organized to make the Semantic Web possible. It also shows how Semantic Web is an extension (not replacement) of classical hypertext web. The illustration was created by Tim Berners-Lee. The stack is still evolving as the layers are concretized. (Note: A humorous talk on the evolving Semantic Web stack was given at the 2009 International Semantic Web Conference by James Hendler.)

Semantic Web technologies As shown in the Semantic Web Stack, the following languages or technologies are used to create Semantic Web. The technologies from the bottom of the stack up to OWL are currently standardized and accepted to build Semantic Web applications. It is still not clear how the top of the stack is going to be implemented. All layers of the stack need to be implemented to achieve full visions of the Semantic Web.

Hypertext Web technologies The bottom layers contain technologies that are well known from hypertext web and that without change provide basis for the semantic web.

Internationalized Resource Identifier (IRI), generalization of URI, provides means for uniquely identifying semantic web resources. Semantic Web needs unique identification to allow provable manipulation with resources in the top layers. Unicode serves to represent and manipulate text in many languages. Semantic Web should also help to bridge documents in different human languages, so it should be able to represent them. XML is a markup language that enables creation of documents composed of semi-structured data. Semantic web gives meaning (semantics) to semi-structured data. XML Namespaces provides a way to use markups from more sources. Semantic Web is about connecting data together, and so it is needed to refer more sources in one document.

Standardized Semantic Web technologies Middle layers contain technologies standardized by W3C to enable building semantic web applications.

Resource Description Framework (RDF) is a framework for creating statements in a form of so-called triples. It enables to represent information about resources in the form of graph - the semantic web is sometimes called Giant Global Graph. RDF Schema (RDFS) provides basic vocabulary for RDF. Using RDFS it is for example possible to create hierarchies of classes and properties. Web Ontology Language (OWL) extends RDFS by adding more advanced constructs to describe semantics of RDF statements. It allows stating additional constraints, such as for example cardinality, restrictions of values, or characteristics of properties such as transitivity. It is based on description logic and so brings reasoning power to the semantic web. SPARQL is a RDF query language - it can be used to query any RDF-based data (i.e., including statements involving RDFS and OWL). Querying language is necessary to retrieve information for semantic web applications. RIF is a rule interchange format. It is important, for example, to allow describing relations that cannot be directly described using description logic used in OWL.

Unrealized Semantic Web technologies Top layers contain technologies that are not yet standardized or contain just ideas that should be implemented in order to realize Semantic Web.

Cryptography is important to ensure and verify that semantic web statements are coming from trusted source. This can be achieved by appropriate digital signature of RDF statements. Trust to derived statements will be supported by (a) verifying that the premises come from trusted source and by (b) relying on formal logic during deriving new information. User interface is the final layer that will enable humans to use semantic web applications.

Notes

Worked examples

Example 1 — a first encounter with Semantic Web Stack

Start with the simplest possible case. Write down what Semantic Web Stack claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Semantic Web Stack before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Semantic Web Stack ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Semantic Web Stack

In research: Semantic Web Stack appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Semantic Web Stack in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Semantic Web Stack is common in secondary-school and first-year university syllabi. It links to neighbouring topics Semantic Web, so understanding it makes those chapters shorter.
In everyday life: Look for Semantic Web Stack outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Semantic Web Stack in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Semantic Web Stack means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Semantic Web Stack out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Semantic Web Stack in simple terms?

Why does Semantic Web Stack matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Semantic Web Stack?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Semantic Web Stack.