science

Named graph

Named graph 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 Named graph rather than just read about it. In short: Named graphs are a key concept of Semantic Web architecture in which a set of Resource Description Framework statements (a graph) are identified using a URI, allowing descriptions to be made of that set of statements such as context, provenance information or other such metadata. Named graphs are a simple extension of the RDF data model through which graphs can be created but the model lacks an effective means of di…

Key takeaways

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

Reference excerpt

Named graphs are a key concept of Semantic Web architecture in which a set of Resource Description Framework statements (a graph) are identified using a URI, allowing descriptions to be made of that set of statements such as context, provenance information or other such metadata. Named graphs are a simple extension of the RDF data model through which graphs can be created but the model lacks an effective means of distinguishing between them once published on the Web at large.

Named graphs and HTTP One conceptualization of the Web is as a graph of document nodes identified with URIs and connected by hyperlink arcs which are expressed within the HTML documents. By doing an HTTP GET on a URI (usually via a Web browser), a somehow-related document may be retrieved. This "follow your nose" approach also applies to RDF documents on the Web in the form of Linked Data, where typically an RDF syntax is used to express data as a series of statements, and URIs within the RDF point to other resources. This Web of data has been described by Tim Berners-Lee as the "Giant Global Graph".

Named graphs are a formalization of the intuitive idea that the contents of an RDF document (a graph) on the Web can be considered to be named by the URI of the document. This considerably simplifies techniques for managing chains of provenance for pieces of data and enabling fine-grained access control to the source data. Additionally, trust can be managed through the publisher applying a digital signature to the data in the named graph. (Support for these facilities was originally intended to come from RDF reification; however, that approach proved problematic.)

Named graphs and RDF stores While named graphs may appear on the Web as simple linked documents (i.e. Linked Data), they are also very useful for managing sets of RDF data within an RDF store. In particular, the scope of a SPARQL query may be limited to a specific set of named graphs.

Example Assume the following (Turtle) RDF document has been placed in a SPARQL-capable store with the name http://example.org/joe.

This data has been written in a more verbose form than necessary to show the triple structures The homepage of the person with the email address mailto:joe@example.org can be obtained using the SPARQL query:

The FROM NAMED here identifies the target graph for the query.

Named graphs and quads Prior to the publication of the papers describing named graphs, there was considerable discussion about fulfilling their role within a store by using an arity greater than that of RDF triple statements: where triples have the form subject predicate object, quads would have a form along the lines of subject predicate object context. Named graphs can be represented this way, as subject predicate object graphname, with the advantage that the graphname part will be a URI, giving the quad Web-global scope compared to arbitrary local statement names. This way of representing quads resp. quad-statements was incorporated in the specification of N-Quads.

Formal definition A paper from the WWW 2005 conference by Carroll et al. includes a formal definition of named graphs.

Specifications Initially specified in the SPARQL Protocol and RDF Query Language specification, named graphs were standardized as an integral part of RDF with version 1.1. These specifications are not entirely aligned with the concepts proposed by Carroll et al. (2005). In particular, while the latter defines a formal semantics for named graphs, named graphs in RDF 1.1 have not specified semantics.

Proposed specifications TriX - Named Graphs in XML TriG - Named Graphs in Turtle N-Quads - Named Graphs in N-Triples

See also Jeni Tennison (2011-07-05). "What Do URIs Mean Anyway?". Jeni's Musings. Jeni Tennison. Retrieved 6 July 2011.

References

Illustrations

Worked examples

Example 1 — a first encounter with Named graph

Start with the simplest possible case. Write down what Named graph 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 Named graph 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 Named graph 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 Named graph

In research: Named graph 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 Named graph 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: Named graph is common in secondary-school and first-year university syllabi. It links to neighbouring topics Graphs, Semantic Web, so understanding it makes those chapters shorter.
In everyday life: Look for Named graph 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 Named graph in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Named graph 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 Named graph out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Named graph in simple terms?

Why does Named graph 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 Named graph?

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 Named graph.