Notation3 Language

Language

The aim of this section is to provide an informal overview of the N3 language and its different features. Where possible, this section is based on the [[[Turtle]]] specification. More formal definitions will follow in the subsequent sections.

N3 document

An N3 document represents an N3 graph in a compact textual form. An N3 graph is a series of N3 statements. These are written as triples consisting of a subject, predicate, and object resource. An N3 resource can be an RDF IRI, literal or blank node; or an N3 graph term, collection, logical implication, variable or N3 builtin. We introduce these types of resources and statements below.

Comments are indicated using a separate '#' and continue until the end of the line.

Simple triples

The simplest N3 statement or triple is a sequence of a subject, predicate, and object resource, separated by whitespace and terminated by '`.`' after each triple.

In the example below, three N3 triples highlight the enmity between Spiderman and the Green Goblin and lists their human-readable names:

For now, we will asssume that a resource is represented either by an IRI or a literal. In general, one uses an IRI to identify an identifiable entity such as a person, place, or thing — a literal is used for a textual or numerical (i.e., datatype) value, such as name, date, height, and so on.

There is no inherent order for N3 or RDF triples. The same is true for the relational database model, i.e., relational tuples or rows do not have an inherent order. Hence, it is a mistake to associate meaning with the order of statements in an N3 document (e.g., assuming that a first listed telephone for Spiderman is their landline, and the second one their mobile number).

Predicate and object lists

As shown in the above example, the same subject (here, Spiderman) will often be described by several N3 statements. To make these N3 statements less cumbersome to write, one can put a semicolon (";") at the end of an N3 statement to describe the same subject in the subsequent statement:

Similarly, a predicate (e.g., name) can often list multiple objects for the same subject (e.g., Spiderman). This can be written by listing the object values separated by a ',':

IRIs

An IRI is used to represent an identifiable entity — such as a person, place, or thing. Until now, we have been writing absolute IRIs [[RFC3987]] (e.g., http://example.org/Spiderman), which include both the namespace (e.g., http://example.org/) and the local name (e.g., Spiderman).

It is often much easier to write an IRI as a prefixed name — e.g., ex:Spiderman, which includes a prefix label (e.g., ex) as a shorthand for the namespace, and the local name (e.g., Spiderman), separated by a colon (":"). The `@prefix` directives associate the prefix label with a namespace IRI. A prefixed name is turned into an absolute IRI by concatenating the namespace IRI with the local name. The following example is equivalent to the original example:

N3 also supports case-insensitive `PREFIX` and `BASE` directives, as does Turtle, to align the syntax with SPARQL (see grammar). These do not have a trailing '.'.

To further simplify prefixed names, one can leave the prefix label empty (e.g., for an often-used namespace):

One can also write relative IRI references, e.g., <#Spiderman>. A relative IRI reference is resolved, i.e., turned into an absolute IRI, by concatenating the base IRI with the local name (e.g., Spiderman). A base IRI is defined using the `@base` directive. For instance, the following is equivalent to the prior example:

Specifics of relative IRI reference resolution are described in .

We recommend listing `@prefix` / `PREFIX` and `@base` / `BASE` declarations at the top of an N3 document. This is not mandatory, however, and they can technically be put anywhere before the prefixed name or relative IRI that relies on the declaration. Subsequent `@prefix` / `PREFIX` directives may "re-map" the same prefix label to another namespace IRI.

Prefixed names are a superset of XML QNames. They differ in that the local name may include:

leading digits, e.g. `leg:3032571` or `isbn13:9780136019701`
non leading colons, e.g. `og:video:height`
reserved character escape sequences, e.g. `wgs:lat\-long`

IRI property lists

In many cases, an IRI occurs only once as an object, and is then further described as a subject in other statements (e.g., see a prior example). The example below illustrates how this may result in difficult-to-read code: to find descriptions of IRI objects such as `tobey-maguire` or `willem-dafoe`, one must scan the full N3 graph, as they are only described near the end.

Using the IRI property list syntax, descriptions of these object IRIs can be directly "embedded" within the object position:

Using basic statements:	Using IRI property lists:

IRI property lists build on the predicate object list syntax to group statements about IRIs. One can use objects lists in this syntax as well.

See also the blank node property list syntax.

See embedding in [[JSON-LD11]] for a discussion of a similar feature in another format.

Literals

Literals are used to represent a textual or numerical (i.e., datatype) value, such as name, date, height, and so on. Numbers (integers, decimals, and doubles) are simply represented using their numerical value, and booleans are represented using true or false:

For details on numerical syntaxes (e.g., decimals, doubles), we refer to the RDF 1.1: Turtle (Section 2.5.2) specification.

Other literals, such as strings, but also dates, binary, octal or hex code, XML or JSON code, or other types of numbers (e.g., shorts), need to be written as datatyped literals. These are represented as a string, followed by the `^^` symbol and the corresponding datatype IRI. (`xsd:string` is the datatype IRI for strings; this is the default and can be omitted, in which case the `^^` MUST also be omitted; in other words, `"example"^^` is not a valid datatyped literal). For instance:

The literal's lexical form will include the characters between the delimiter quotes (e.g., 2001-08-10).

The language of the string literal can be indicated using the @ symbol and the corresponding language tag (as defined in [[BCP47]] — find the registry in [[LNG-TAG]]). For instance:

The reading direction can be described together with the language [[BCP47]], using the i18n namespace:

If no datatype IRI or language tag is given, the datatype xsd:string will be assumed. In case a language tag is given or a i18n "datatype" is used, the datatype rdf:langString is inferred. It is not possible to specify both a datatype IRI and a language tag.

There are also other ways to describe the language tag and base direction of RDF literals, see Compound literals. Please note that these various ways are still in flux, see the "text direction" discussions in the RDF-star working group.

Integers, decimals, doubles, and booleans may also be written as string literals with the appropriate datatype IRI (e.g., `"8"^^xsd:integer` or `"true"^^xsd:boolean`).

In case the the string literal itself contains the string delimiter (e.g., double quotes), or includes newlines, other string delimiters can be used, i.e., single quotes or compound delimiters """ or '''. Alternatively, one can also use a '\' for escaping the delimiter each time it occurs within a string literal. For instance:

The escape symbol '\' (U+005C) may only appear in a string literal as part of an escape sequence. Other restrictions within string literals depend on the delimiter:

Literals delimited by ' may not contain the characters ', _LF (U+000A), or _CR (U+000D).
Literals delimited by " may not contain the characters ", _LF, or _CR.
Literals delimited by ''' may not contain the sequence of characters '''.
Literals delimited by """ may not contain the sequence of characters """.

Blank Nodes

When describing resources in RDF, you can run into the following situations:

It is not worth minting a new IRI for the resource, as it is unlikely that other N3 graphs will refer to it.
There likely already exists an IRI for the resource, and we don't want to do an extensive search to find out what it is.

Instead, you can use blank nodes to talk about resources. They are existential variables; that is, they state the existence of a thing without identifying it. Blank nodes can be represented in several ways, as described below. For details, please refer to ([[[RDF11-CONCEPTS]]]).

Blank node identifiers

A blank node can be represented by a blank node identifier, which is unique within the N3 graph, expressed as _:someLabel. Then, we use this identifier within our N3 graph to describe the corresponding resource, same as with an IRI.

For instance, this example shows that the Mona Lisa has an unidentified tree in its background. We don't want to concretely identify this tree, but we do want to describe it — such as the painting it is in, and the type of tree:

In this example, we minted a blank node identifier _:someTree to represent the resource that we want to describe. Note that this identifier is only usable within our local N3 graph — if you want other N3 graphs to describe it, you should represent it using an IRI.

Blank node property lists

Using a blank node identifier requires introducing a new identifier for each blank node. In many cases, however, a blank node occurs only once as an object, and is then further described as a subject in other statements, such as in the prior example. In those cases, a more convenient syntax can be used.

The example below shows a more elaborate example: identifiers `_:a` and `_:t` are used as object in only one statement, and are then described as subject in other statements. Using the blank node property list syntax, these cases can be represented as follows:

Using blank node identifiers:	Using blank node property lists:

See also the IRI property list syntax. However, note that you cannot use that syntax (`id` keyword) with blank node identifiers.

The "blank node property list" syntax is especially useful in cases where a blank node occurs only once as an object. When the blank node occurs several times as an object, such as when describing multiple people with the same address, it is better to use blank node identifiers. For instance:

We can still use the blank node property list syntax for describing the town, as this blank node still only occurs once as object.

Blank node use cases

Below, we summarize typical use cases where blank nodes are used to describe resources.

Unknown resources: we might want to state that the Mona Lisa painting has in its background an unidentified tree, which we know to be a cypress tree. We could mint an IRI such as "mona-lisa-cypress-tree", but we feel that would be redundant — we simply want to describe the tree, such as the painting it is in, and the type of tree. We're not particularly interested in allowing other N3 graphs to refer to the tree. Moreover, there may already exist an IRI for that particular tree, and we don't want to mint another IRI to refer to the same tree (nor do we want to lookup this existing IRI).

Composite information: when describing composite pieces of information, such as street addresses, telephone numbers and dates, it is often unlikely that anyone outside this N3 graph would need to refer to this address or its pieces. Hence, it would be redundant to mint an IRI just for the purpose of structuring this information. Instead, one can use a blank node to connect the "composed" pieces of information, e.g., the street address, to its composite values, e.g., street name, number, and city, as shown in this example.

N-ary relations: blank nodes are a convenient way to represent n-ary relations in N3.

Compound literal: to represent language-tagged strings, see section Compound literals.

Collections

We often need to describe ordered collections of things, e.g., a book written by several authors, listing the students in a course, or the software modules within a package. N3 supports collections as first-class citizens to represent ordered collections of resources enclosed by parentheses ("( )"). The contained resources are called members.

For instance:

This states that the value of the author property is the collection resource.

Any additional meaning is not given by the N3 semantics. For instance, this example does not imply that each member (e.g., :deborah) can be considered as a value of the author property — i.e., the author property does not "distribute" across the members. For that matter, it is also not implied that the first member put the most effort into the book. Any additional meaning, such as each member being an author of the book, and the ordering reflecting the authors' effort, would always be application-specific.

In general, to implement such application-specific meanings, N3 rules could be used. Alternatively, one could use an object list to explicitly state that each of these resources are authors of the book:
`:description_logic_handbook :author :deborah, :daniele, :peter .`
However, since RDF (and thus N3) statements do not have an inherent order, this example loses meaning as we no longer know who can be considered the "first" author.

To an extent, an N3 collection is equivalent to the more verbose RDF Collection vocabulary. We refer to the original N3 submission for the additional axioms needed for this equivalency.

In N3, collections may occur as subjects, predicates or objects in a statement. For instance:

Or even:

As before: any meaning that goes beyond the fact that 3 collection resources are involved in this statement, would be application-specific.

Graph Terms

It is often useful to attach metadata to groups of triples — to give the provenance, context, or version of the information, our opinion on the matter, and so on. We can use graph terms to quote RDF graphs, and then describe the graph term using N3 statements. For instance:

Essentially, a graph term represents an occurrence of an RDF graph — i.e., a quoting or citing of the graph. Importantly, a graph term does not assert the contents of the RDF graph as being true (e.g., :cervantes dc:wrote :moby_dick). In fact, the graph term is interpreted as a resource on its own.

As with collections, graph terms can be used in any position in an N3 statement.

As they represent a quoting of RDF graphs, graph terms are not "referentially transparent". For instance:

This N3 statement states that Lois Lane believes that Superman can fly. Even if it is known that :Superman is the same as :ClarkKent, one cannot infer from this that Lois Lane believes that :ClarkKent can fly. Indeed, this is an accurate depiction of Lois Lane's statement at the time — as she did not know that Superman is Clark Kent at that point, she would certainly not be saying that Clark Kent can fly.

N3 Rules

N3 supports declarative programming by allowing to make statements about the world, including logical implications, or N3 rules, which can be loosely compared to If-Then statements. Based on the N3 semantics, so-called inferences can be drawn from these statements. An N3 reasoner can draw such inferences automatically, to support problem solving, decision making, or simply enriching your Knowledge Graph.

For instance, the following is an N3 rule:

This is a logical construct, such as a conjunction (AND) and disjunction (OR). Stating such a logical implication means that, in case the rule premise is true (it is raining), the rule conclusion must be true as well (it is cloudy). If this is not the case — raining does not imply that it is cloudy — the implication would be false. However, this is not possible, since all statements in N3 (and RDF) are true by default.

Hence, when the premise holds, then we can safely infer the conclusion. This is also referred to as firing the rule. For the example above, if we state `:weather a :Raining`, then we can safely infer `:weather a :Cloudy`.

An N3 rule is actually a N3 statement, where the subject and object constitute graph terms, and the predicate is `log:implies`, with symbol `=>` as syntactic sugar.

Rule Variables

N3 rules are more useful when they include variables. For instance, the following includes a universal variable (prefixed by `?`):

This states that the N3 rule is true for each value of variable `?x`: when the premise is true for a particular value for `?x` (being a super hero), then the conclusion must be true for that value as well (being imaginary). For the example above, the premise is true for value `:spiderman`, meaning we can infer the conclusion for that value, i.e., `:spiderman a :Imaginary`.

More technically, the triples in the rule premise (e.g., `?x a :SuperHero`) can be seen as triple patterns. In order to fire the rule, these triple patterns are matched to concrete triples in the N3 document. If a match is successful, concrete resources from the matching triple (e.g., `:spiderman`) are bound to the triple pattern's variables (e.g., `?x`). These bound variable values are then used in the inferred conclusion (e.g., `:spiderman a :Imaginary`).

Rule Chaining

In practice, a pivotal feature is that N3 rules can be "chained": a rule can depend on the results of other rules. For example:

The third N3 rule relies on the rule conclusion (`:locomotion`) of the first two rules: if one of those rules fire, i.e., inferring a flying locomotion for a resource, then the third rule would fire as well, i.e., inferring that the resource would be a suitable observer for a street with heavy traffic. This allows for a modularization of N3 code: the first two rules separately decide when something supports a flying locomotion; the third rule determines what the general effects of flying locomotion are.

Variable names only have to be unique within a rule, and not across rules. For instance, in the prior example, we simply could have named every variable `?x`. As with general coding practices, it is typically a good idea to give variables a meaningful name.

An N3 reasoner, which can draw inferences from N3 rules, can operate in forward chaining, backward chaining, or some hybrid mode. An N3 rule can also indicate which mode should be used, by using the appropriate predicate. Up until now, we have used `=>`, which is syntactic sugar for `log:implies` and directs the reasoner to operate in forward chaining mode. The `<=` predicate, which is syntactic sugar for `log:impliedBy`, indicates a backward chaining mode.

For instance, the following is equivalent to the prior example and combines forward and backward chaining:

In a nutshell, forward reasoning presents a bottom-up approach: starting from a set of initial and inferred statements, a reasoner will fire any N3 rule where the premise holds, each time adding the inferences to the set, until no more N3 rules can be fired. Backward chaining is a top-down approach: given a query, such as `?x :locomotion :flying`, the reasoner will search for any rules with conclusions that may satisfy the query (e.g., first and second rule). Then, it will check whether the premises of those rules hold, which may, in itself, require searching for rules with matching conclusions. Regarding general expressivity, these two reasoning modes can be considered equivalent. A detailed discussion of these two reasoning modes, their subtle differences and impacts on performance, is beyond the scope of this specification.

N3 Builtins

An N3 builtin is used within an N3 rule to implement an arbitrary operation on an N3 resource or even an entire N3 document. Builtins include mathematic, string, time and cryptography operators, operations on collections and graphs, and logical operations in general.

Lists of built-ins

Built-ins are denoted by a controlled IRI defined in one of the core namespaces:

Crypto – http://www.w3.org/2000/10/swap/crypto#,
List – http://www.w3.org/2000/10/swap/list#,
Log – http://www.w3.org/2000/10/swap/log#,
Math – http://www.w3.org/2000/10/swap/math#,
String – http://www.w3.org/2000/10/swap/string#, and
Time – http://www.w3.org/2000/10/swap/time#.

Simple Builtins

As a simple example, the rule below uses the `math:quotient` builtin to calculate a person's height in meters:

An N3 builtin is used as the predicate in an N3 builtin statement, where the subject and object act as input or output arguments. In the example above, the second triple constitutes a builtin statement: the subject is the input, as `math:quotient` calculates the quotient of the subject collection elements (i.e., the person's height in cm and 100); the object constitutes the output, as the result is then bound to the object variable `?m`.

Builtins with Multiple Results

N3 builtins can generate multiple results. Below, we use the `list:iterate` builtin to iterate over collection elements, and subsequently constructs a string for each element:

The `list:iterate` builtin iterates over all elements in the subject collection (`?finalists`). For each element, it binds its index, and the element itself, to the variables in the object collection (`?i` and `?finalist`, respectively). Hence, the `list:iterate` builtin generates multiple sets of bindings for the `?i` and `?finalist` variables:
( ?i = 1, ?finalist = :flash )
( ?i = 2, ?finalist = :superman )
( ?i = 3, ?finalist = :spiderman )

For each set of bindings, the `string:concatenation` builtin concatenates the resources in the subject collection, and binds the result to the object variable (`?entry`). This will lead to the following object values:
"`1. :flash`" , "`2. :superman`" , and "`3. :spiderman`"

A builtin statement can be seen as a triple pattern that, for each builtin result, yields one or more "matching" triples depending on the builtin. For the example above:
( :flash :superman :spiderman ) list:iterate ( 1 :flash ) . ( :flash :superman :spiderman ) list:iterate ( 2 :superman ) . ( :flash :superman :spiderman ) list:iterate ( 3 :spiderman ) .
As with a SPARQL query, for each "matching triple", a join is attempted with the remaining triples in the rule premise. Hence, for each matching triple, the `string:concatenation` builtin statement is evaluated. Finally, for each consistent set of variable bindings, the rule conclusion is instantiated and inferred.

Scoped Negation as Failure (SNAF)

N3 builtins can also operate on a local graph term or even an entire N3 document. The `log:collectAllIn`, `log:forAllIn`, and `log:notIncludes` builtins are logical operators that support a negation-as-failure scoped on the builtin statement object: the object can be a graph term or a blank node, in which case the current document is the scope. For instance, the rule below uses `log:collectAllIn` to collect all of spiderman's defeated villains found in the current document:

The `log:collectAllIn` builtin accepts as subject a collection that includes:

a variable of which the values will be collected (`?enemy`),
a where clause with triple patterns that constrain this variable, and
a variable bound to the resulting collection of values (`?enemies`).

The where clause is evaluated on the given scope, in this case, the current N3 document; all potential results beyond this scope are considered false (SNAF). This leads to the following result:
:spiderman :defeatedEnemies ( :green-goblin :doctor-octopus )

The example below uses `log:forAllIn` to determine whether a super-hero's identity is safe:

The `log:forAllIn` builtin accepts as subject a collection with two clauses of a logical implication. If, for all cases where the first clause holds, the second clause holds as well, then the logical implication is true. In this example, the implication is true when, for each person who knows the identity of spiderman, this person can keep a secret. In this case the rule will fire, as both `mary-jane-watson` and `aunt-may` can keep secrets.

In the two examples above, the blank node object `_:t` indicates the current N3 document as scope. Alternatively, a graph term can be used as the scope as well. This is illustrated in the `log:notIncludes` example below.

The `log:notIncludes` builtin checks whether the given scope does not include a given clause. The example below uses a graph term as scope, instead of the current N3 document, as was the case for the prior two examples. The rule finds any of spiderman's enemies who have not been defeated, at least, as reported by the Daily Bugle:

For each of spiderman's enemies (`?enemy`), the rule checks whether the graph term `?graph`, as reported by the `:daily_bugle`, does not include any statement where the enemy has been defeated. If so, we infer that this enemy is undefeated, in this case, `:sandman`.

The counterpart of `log:notIncludes` is `log:includes`, which checks whether the given object scope includes a given clause.

Access Online Knowledge

To dynamically retrieve online knowledge within an N3 rule, log:semantics and log:conclusion builtins allow pulling in, parsing, and reasoning over logical expressions from online sources.

In the rule below, the `log:semantics` builtin retrieves an online source and subsequently parses it a graph term:

Subsequently, `log:collectAllIn` is used to collect all persons found within the online source.

The `log:conclusion` builtin allows generating the closure of a given graph term, i.e., extending the graph with all applicable rule inferences. This includes graph terms retrieved and parsed from online sources. For example:

Instead of simply printing the inferences, one could, e.g., use the `log:forAllIn` builtin to check whether all persons listed in the online source are indeed inferred to be animals as well.

Resource Paths

Similar to SPARQL property paths, N3 resource paths concisely express paths between resources, when intermediary resources on the path are not relevant. In practice, resource paths are most useful in N3 rules.

A resource path starts from a subject resource, followed by one or more predicates; each predicate is separated by a directional indicator to follow the predicate either forward (`!`) or in reverse (`^`). For example, the following example describes the city of Joe's mother's office's address:

In this example, the intermediary resources — Joe's mother, her office, and its address — are not described or referenced further, so the more concise resource path syntax can be used.

The expansion of this shorthand syntax uses blank nodes to express the path between the two resources. The example above is equivalent to the following (using blank node identifiers for clarity):

In other words, each predicate in resource path is expanded into a statement, with as subject either the starting resource, or prior blank node object; and as object a newly minted blank node.

Relations can also be followed in reverse using the reverse (`^`) indicator. The following example, starting from `joe`, follows the `hasMother` predicate to Joe's mother, and then follows the `hasMother` predicate in reverse (thus pointing to someone who has the same mother):

This could equally well be represented by the more verbose:

In SPARQL, a property path is used in the predicate position to describe a string of relationships between a subject and an object resource. In contrast, an N3 resource path is most often used in the subject or object position. Using a resource path in the predicate position, although technically allowed, is often a mistake. For instance, the following N3 resource path:
    `:joe :hasAddress!:hasCity "Metropolis" .`
Would lead to the following expansion:
    `:joe _:bn_1 "Metropolis" .`
    `:hasAddress :hasCity _:bn_1 .`
Which is likely not the intention of the author.

EBNF Grammar

The Turtle grammar was used as the starting point for the N3 grammar, which was subsequently adapted and extended with N3 constructs.

The N3 Working Group made the following decisions that modify the N3 grammar as originally presented in [[N3]]:

Dropping the @keywords declaration. It is complex and difficult to explain. Also, when using the declaration, N3 documents look wholly different from when it is not being used, since it allows local names in the default namespace to be listed without the ":" symbol.
Supporting all verb and boolean keywords (is .. of, has, a, true, false) both with and without "@" prefix. Turtle supports the a keyword, i.e., without an "@", but requires the symbol for the @prefix and @base declarations. The original N3 grammar required the "@" prefix for all verb and boolean keywords. Hence, this decision was made for compatibility with Turtle as well as to avoid an unintuitive grammar, i.e., where some keywords have the "@" prefix and some don't.
Representing an inverted property using the <- symbol. The original N3 grammar allowed the inverting of a property by using the @is .. @of construct. But, this construct can be unintuitive when property names are more verbosely specified (e.g., :hasFather), leading to statements such as ?x @is :hasFather @of ?y. The is .. of construct is still supported, but the above statement can now be represented as follows: ?x <- :hasFather ?y.

Whitespace

White space (WS production) is used to separate terminals. The amount and type of white space (e.g., newline (`%0A`) or space (`%20`)) is only significant within terminals.

We note that the IRIREF production only allows IRI-encoded white spaces.

Comments

Comments are indicated using a "#" symbol outside an N3 terminal (e.g., IRIREF, STRING) and will continue until the end of the line (indicated by \r, \n or \f) or end of file, if there is no end of line marker.

All recognized comment terminals will be skipped by the grammar (i.e., a resulting parser will not call listener or visitor code when encountering a comment.)

Escape sequences

There are three forms of escapes used in N3 documents:

Escape sequences in string literals. These are characters that are traditionally escaped in strings:

Escape sequence	Unicode code point
'\t'	U+0009
'\b'	U+0008
'\n'	U+000A
'\r'	U+000D
'\f'	U+000C
'\"'	U+0022
'\''	U+0027
'\\'	U+005C

(see the ECHAR production)

Numeric escape sequences. These represent Unicode code points:

Escape sequence	Unicode code point
'\u' hex hex hex hex	A Unicode character in the range U+0000 to U+FFFF inclusive corresponding to the value encoded by the four hexadecimal digits interpreted from most significant to least significant digit.
'\U' hex hex hex hex hex hex hex hex	A Unicode character in the range U+0000 to U+10FFFF inclusive corresponding to the value encoded by the eight hexadecimal digits interpreted from most significant to least significant digit.

(see the UCHAR production)

Escape sequences in local names. These escape the following reserved characters in the local name part of prefixed names: _ ~ . - ! $ & \ ( ) * + , ; = / ? # @ % (see the PN_LOCAL_ESC production)

IRI resolution

Relative IRIs are resolved with base IRIs using the algorithm in [[[RFC3986]]] [[RFC3986]] Section 5.2 "Relative Resolution" as supplemented by Section 6.5 of [[[RFC3987]]] [[RFC3997]].

The N3 @base or BASE directive can be used to define the Base IRI, per [[RFC3986]] Section 5.1.1 "Base URI Embedded in Conent". Each `@base` or `BASE` directive sets a new In-Scope Base IRI, relative to the previous base IRI.

Resource path resolution

Resource paths are resolved into zero or more N3 triples, and a single N3 triple element which is used as the expression value of the path.

This section describes two logically equivalent algorithms for transforming a path into a set of N3 triples, and providing a resource to use as the effective subject, predicate, or object in place of the original path expression.

Right to Left Algorithm

The first algorithm describes a means of processing a path starting from the right hand side of the path. This is useful for an implementation based processing an Abstract Syntax Tree generated by a parser, or where the entire path is treated as a token and language-specific tools are used to process it further.

Processing is performed by recursively processing the path |p|, in reverse, from the last directional indicator (`!`) or (`^`). The result of resolving |p| into an expression and set of emitted N3 triples MUST be equivalent to using the following algorithm:

If |p| matches the pathItem production, then |p| can be reduced no further, return |p| as the result.
Otherwise, separate the |p| into two components p_n-1 and pred_n on the last occurrence of the directional indicator dir_n.
Create obj_n by invoking this algorithm recursively using p_n-1 for |p|.
Create a novel blank node B_n.
If dir_n is "`!`", emit a new N3 triple (obj_n pred_n B_n).
Otherwise, dir_n is "`^`", emit a new N3 triple (B_n pred_n obj_n).
Return B_n as the result.

Starting with the path |p| set to `:john!:father`:

Step 1 does not apply, as `:john!:father` is not a pathItem.
Step 2 separates `:john!:father` into p_n-1 `:john`, pred_n `:father`, and dir_n "`!`".
Step 3 sets obj_n by calling the algorithm recursively using |p| `:john`.
- Step 1 returns `:john` as it matches a pathItem.
- obj_n is `:john`.
Step 4 creates B_n.
Step 5 matches because dir_n is "`!`". The triple (`:john` `:father` B_n) is emitted.
Step 7 returns B_n.

Starting with the path |p| set to `john^:father!:mother`:

Step 1 does not apply, as `john^:father!:mother` is not a pathItem.
Step 2 separates `:john^:father!:mother` into p_n-1 `:john^:father`, pred_n `:mother`, and dir_n "`!`".
Step 3 creates B_n.
Step 4 sets obj_n by calling the algorithm recursively using |p| `:john^:father`.
- Step 1 does not apply, as `:john^:father` is not a pathItem.
- Step 2 separates `:john^:father` into p_n-2 `:john`, pred_n-1 `:father`, and dir_n-1 "`^`".
- Step 3 creates B_n-1.
- Step 4 sets obj_n-1 by calling the algorithm recursively using |p| `:john`.
  - Step 1 returns `:john` as it matches a pathItem.
  - obj_n-1 is `:john`.
- Step 6 matches because |dir| is "`^`". The triple (B_n-1 `:father` `:john`) is emitted.
- Step 7 returns B_n-1.
- obj_n is B_n-1.
Step 5 matches because |dir| is "`!`". The triple (B_n-1 `:mother` B_n) is emitted.
Step 7 returns B_n.

Left to Right Algorithm

The second algorithm describes a means of processing a path starting from the left hand side of a path. This is useful for an implementation based on the parser productions described in the grammar that create events in this order (i.e., event-based).

Processing is performed by iteratively processing the path p, in the forward direction, from the first directional indicator (`!`) or (`^`). The result of resolving p into an expression and set of emitted N3 triples MUST be equivalent to using the following algorithm:

Initialize |n| to `0` and B₀ to the first pathItem in |p|. Repeat the following algorithm steps until return.

B₀ starts as the first pathItem in |p|, but is updated to a novel blank node on subsequent iterations.

If |n| equals the number of directional indicators in |p|, return B_n.
Increment |n|, set B_n to a novel blank node, set dir_n to the next (n_th) directional indicator dir_n (if any), set pred_n to the next pathItem (if any).
If dir_n is "`!`", emit a new N3 triple (B_n-1 pred_n B_n).
Otherwise, if dir_n is "`^`", emit a new N3 triple (B_n pred_n B_n-1).

Starting with the path |p| set to `:john^:father!:mother`; |n| is `0` and B₀ is `:john`:

Step 1 does not apply, as |n| is `0`.
Step 2 increments |n| to `1`, sets B₁ to a novel blank node, dir₁ to "`^`", and pred₁ to `:father`.
Step 4 emits (B₁ `:father` `:john`), as dir₁ is "`^`"
Looping back to step 1, |n| is `1`:
- Step 1 does not apply, as |n| is `1`.
- Step 2 increments |n| to `2`, sets B₂ to a novel blank node, dir₂ to "`!`", and pred₂ to `:mother`.
- Step 3 emits (B₁ `:mother` B₂), as dir₂ is "`!`"
- Looping back to step 1, |n| is `2`:
  - Step 1 returns B₂ as |n| is `2`, which is the number of directional indicators in `:john^:father!:mother`.

Syntax shorthands

Similar to Turtle, N3 provides a special shorthand syntax for commonly used URIs. This may only be used in the predicate position. From the original Team Submission [[N3]]:

Shorthand	URI
`a`	`<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>`
`=`	`<http://www.w3.org/2002/07/owl#sameAs>`
`=>`	`<http://www.w3.org/2000/10/swap/log#implies>`
`<=`	`<http://www.w3.org/2000/10/swap/log#impliedBy>`

Grammar

A textual version of this grammar may be found here.

Relationship to Other Languages

Turtle

N3 is a superset of [[[turtle]]], meaning that all valid Turtle documents will be valid in N3 as well. The inverse is not true, i.e., a valid N3 document will not always be valid in Turtle.

The current N3 grammar started from the Turtle grammar which was adapted and extended to be in line with the original N3 grammar. Hence, many of the grammar productions will be much more similar to the Turtle grammar than the initial N3 grammar.

Important differences with Turtle are the following:

Literals are allowed at any s/p/o position (i.e., subject, predicate or object) in a statement. See the pathItem production, which is (eventually) referenced by the "subject", "predicate" and "object" productions.
N3 includes graph terms (i.e., between "{" and "}"), which are allowed in any s/p/o position in a statement. See the pathItem production.
Quick-variables (e.g., "?x"), which are allowed in any s/p/o position in a statement. See the pathItem production.
A path syntax, comparable to (but not quite as extensive as) the SPARQL 1.1 Property Path syntax. See the path production.
The possibility to invert the predicate within a statement. See the predicate production.
An additional set of keywords, including "is .. of", "has", "=", "=>", "<=", in addition to Turtle's "a" keyword (among others). All keywords can be optionally preceded by "@", for consistency with the "@prefix" and "@base" keywords.

SPARQL

The SPARQL 1.1 Query Language (SPARQL) [[SPARQL11-QUERY]] uses a Turtle-style [[turtle]] syntax for its TriplesBlock production. Differences between Turtle and SPARQL are elaborated in the Turtle specification.

Below, we indicate some important differences between the TriplesBlock production and N3:

Like N3, SPARQL permits literals as the subject of RDF triples, but, in contrast to N3, it does not allow literals as the predicate of RDF triples. Similarly, N3 allows for blank node property lists and collections in any position, whereas SPARQL only allows them in the subject or object position.
Like N3, SPARQL permits variables in any part of the triple. But, in contrast to N3, SPARQL allows writing variables as both ?name and $name, whereas N3 only allows ?name.
N3 allows prefix and base directives anywhere outside of a triple. In SPARQL, they are only allowed in the Prologue (i.e., at the start of the SPARQL query). However, in general, we also recommend listing prolog and base directives at the start of N3 documents.
In N3, most keywords (including @prefix and @base directives) are case sensitive, but most keywords in SPARQL are case-insensitive (aside from a). An exception in N3 are the PREFIX and BASE directives, which are derived from SPARQL and are case insensitive in N3 as well.
The N3 path syntax resembles the SPARQL 1.1 Property Path syntax, but there are important differences:
- It is assumed that the path starts from a resource (IR) instead of a property (IP). Hence, they are meant to be used in the subject and object positions, rather than the predicate position as is the case for SPARQL 1.1 property paths. This has important repercussions on how paths are resolved. Note that paths are unrelated to the inverted notation ^ for predicates (see the predicate production)
- Compared to SPARQL, N3 only supports the SequencePath and InversePath expressions, but with syntactic differences: the '!' symbol is used to separate path items, whereas the '^' symbol is used to indicate an inverse predicate.

For more information, see the SPARQL Grammar section of [[[SPARQL11-QUERY]]].

TriG

[[[TRIG]]] is itself a superset of the Turtle syntax and includes a compact way to write RDF datasets, i.e., sets of named graphs. In particular, TriG allows the specification of so-called graph statements, which are a pair of an IRI or blank node label and a group of triple statements surrounded by "{" and "}".

For instance:

N3 is not directly compatible with TriG as it does not support this graph statement notation. Nevertheless, since N3 supports graph terms as part of regular N3 statements, authors can use the N3 Named Graphs extension; this extension allows associating names or identifiers with graph terms. For instance:

The N3 Named Graphs extension defines a set of builtins (used as predicates) to associate names or identifiers with graph terms, which then become "named graphs". Moreover, each predicate has a well-defined semantics on how the named graph should be interpreted: as graph terms (the default N3 interpretation), a partitioning of triples within a dataset context, sets of triples with their own isolated contexts, or specifying relations between local and online graphs.

Status of this document

Introduction

Language

N3 document

Simple triples

Predicate and object lists

IRIs

IRI property lists

Literals

Blank Nodes

Blank node identifiers

Blank node property lists

Blank node use cases

Collections

Graph Terms

N3 Rules

Rule Variables

Rule Chaining

N3 Builtins

Lists of built-ins

Simple Builtins

Builtins with Multiple Results

Scoped Negation as Failure (SNAF)

Access Online Knowledge

Resource Paths

EBNF Grammar

Whitespace

Comments

Escape sequences

IRI resolution

Resource path resolution

Right to Left Algorithm

Left to Right Algorithm

Syntax shorthands

Grammar

Relationship to Other Languages

Turtle

SPARQL

TriG

Design Patterns

N-ary Relations

Using sets of binary relations

Using collections

Compound literal

Graph Terms

Embedding N3 in HTML documents

Internet Media Type, File Extension and Macintosh File Type

Changes since the Team Submission