This tutorial will walk you through what rdflib.js can do.

Introduction

rdflib.js is a library for fetching, parsing and serializing RDF data
in various formats/serializations (Turtle, RDF/XML, RDFa, etc).

It helps to be familiar with general RDF terminology before working with this
library:

RDF Primer

Namespace shortcuts

The system uses javascript objects for RDF symbols. Generating them for
predicates is simplified by using a namespace function, turning them into
prefixes:

So now, instead of typing the whole URI for your predicate, i.e.:

You can type:

RDF term types

These are types of nodes in the RDF graph. We call them terms because they are
like terms in a language when you think of RDF as a real language.

What How Term type
Node identified by a URI x = $rdf.sym(uri) symbol
Blank node x = $rdf.bnode() ‘bnode’
Untyped Literal x = $rdf.literal('abc') literal
Typed Literal x = $rdf.literal('8080', undefined, XSD('int')) literal
Literal with language x = $rdf.literal('car', 'en') literal
Ordered list x = $rdf.list([node1, node2]) collection

Creating a data store (graph)

Fetch data into the store from the Web

You can also load data from an existing URL into the store you just created.

Load data into the store from a buffer/string

Sometimes you may need to load data coming from a file or a buffer. Rdflib offers a helper function that simply parses a string (containing RDF). This function takes the following parameters:

  • body – the RDF statements (content to be parsed)
  • store – the graph/store object where the RDF should be parsed to
  • uri – the URI of the resource (named graph)
  • mimeType – the mime type corresponding to the data that needs to be parsed

Using data in the store

There are two ways to look at RDF data in a store. You can synchronously use the
each() and any() methods and statementsMatching(), or you can do a query
which returns results asynchronously.

The each(), any() and statementsMatching() take a pattern of subject,
predate, object and source, where for each() and any() one of s p and o are
undefined and source may be undefined or not. For example, using $rdf.sym() to
make an object for an RDF node (symbol),

or using the vocabulary namespace straight away

Wildcards

When one of the terms of the triple is set as undefined, it then serves as a
wildcard. In this case, the formula returns the object of a matching triple.

Alternatively, you get a javascript array of objects using each().

Wildcards in statements

An alternative to using each() comes in the form of statementsMatching(),
which returns an array of statements that match a specific triple pattern.

For example, we can obtain all the statements having foaf:knows as a
predicate. This way we obtain an array of all the people and all the friends
they have. Then it’s up to us to decide what information we want to use, may
that be the subjects or the objects of those statements.

Adding data

The add(s, p, o, w) method allows a statement to be added to a formula. The
optional w argument can be used to keep track of which resource was the source
(URI) for each triple. Objects in a quad can either be nodes (URIs) or literals.

To create a node, use $rdf.sym(). To create a plain literal, use a simple quoted
string.

For a literal with a language attribute and/or data type, use $rdf.lit(). The example
below shows how you can set a dateTime data type for a date value, where dateTime
is an RDF property described by the XSD vocabulary.

For a language tag, you can pass the shortname value (e.g. en) to the second parameter of
the $rdf.lit() function.

The each(), any() and statementsMatching() functions in fact can take a
fourth argument to select data from a particular source. For example, I want to
find only the friends in my foaf file, so I force use of my foaf file as the
w argument.

Examples of applications using rdflib.js

Here are a few examples of applications that use rdflib.js. For a full list, please see the Solid app list.