# RDF::N3 reader/writer and reasoner

Notation-3 reader/writer for RDF.rb .

## Description

RDF::N3 is an Notation-3 parser and reasoner for Ruby using the RDF.rb library suite.

Reader inspired from TimBL predictiveParser and Python librdf implementation.

## Uses CG Specification

This version tracks the W3C N3 Community Group Specification which has incompatibilities with the Team Submission version. Notably:

- The
`@keywords`

declaration is removed, and most form of`@`

keywords (e.g.,`@is`

,`@has`

,`@true`

) are no longer supported. - Terminals adhere closely to their counterparts in Turtle.
- The modifier
`<-`

is introduced as a synonym for`is ... of`

. - The SPARQL
`BASE`

and`PREFIX`

declarations are supported. - Implicit universal variables are defined at the top-level, rather than in the parent formula of the one in which they are defined.
- Support for explicit existential and universal variables (
`@forAll`

and`@forSome`

) has been removed. Quick variables are the standard for universal quantification and blank nodes for existential, but scoping rules are different: Quickvars have top-level scope, and blank nodes formula scope.

This brings N3 closer to compatibility with Turtle.

## Features

RDF::N3 parses Notation-3, Turtle and N-Triples into statements or quads. It also performs reasoning and serializes to N3.

Install with `gem install rdf-n3`

## Limitations

- Support for Variables in Formulae. Existential variables are quantified to RDF::Node instances, Universals to RDF::Query::Variable, with the URI of the variable target used as the variable name.

## Usage

Instantiate a reader from a local file:

```
RDF::N3::Reader.open("etc/foaf.n3") do |reader|
reader.each_statement do |statement|
puts statement.inspect
end
end
```

Define `@base`

and `@prefix`

definitions, and use for serialization using `:base_uri`

an `:prefixes`

options

Write a graph to a file:

```
RDF::N3::Writer.open("etc/test.n3") do |writer|
writer << graph
end
```

### Reasoning

Experimental N3 reasoning is supported. Instantiate a reasoner from a dataset:

```
RDF::N3::Reasoner.new do |reasoner|
RDF::N3::Reader.open("etc/foaf.n3") {|reader| reasoner << reader}
reader.each_statement do |statement|
puts statement.inspect
end
end
```

Reasoning is performed by turning a repository containing formula and predicate operators into an executable set of operators (similar to the executable SPARQL Algebra). Reasoning adds statements to the base dataset, marked with `:inferred`

(e.g. `statement.inferred?`

). Predicate operators are defined from the following vocabularies.

When dispatching built-in operators, precedence is given to operators whos operands are fully evaluated, followed by those having only variable output operands, followed by those having the fewest operands. Operators are evaluated until either no solutions are derived, or all operators have been completed.

Reasoning is discussed in the Design Issues document.

#### RDF List vocabulary http://www.w3.org/2000/10/swap/list#

`list:append`

(See RDF::N3::Algebra::List::Append)`list:first`

(See RDF::N3::Algebra::List::First)`list:in`

(See RDF::N3::Algebra::List::In)`list:iterate`

(See RDF::N3::Algebra::List::Iterate)`list:last`

(See RDF::N3::Algebra::List::Last)`list:length`

(See RDF::N3::Algebra::List::Length)`list:member`

(See RDF::N3::Algebra::List::Member)

#### RDF Log vocabulary http://www.w3.org/2000/10/swap/log#

`log:conclusion`

(See RDF::N3::Algebra::Log::Conclusion)`log:conjunction`

(See RDF::N3::Algebra::Log::Conjunction)`log:content`

(See RDF::N3::Algebra::Log::Content)`log:dtlit`

(See RDF::N3::Algebra::Log::DtLit)`log:equalTo`

(See RDF::N3::Algebra::Log::EqualTo)`log:implies`

(See RDF::N3::Algebra::Log::Implies)`log:includes`

(See RDF::N3::Algebra::Log::Includes)`log:langlit`

(See RDF::N3::Algebra::Log::LangLit)`log:n3String`

(See RDF::N3::Algebra::Log::N3String)`log:notEqualTo`

(See RDF::N3::Algebra::Log::NotEqualTo)`log:notIncludes`

(See RDF::N3::Algebra::Log::NotIncludes)`log:outputString`

See RDF::N3::Algebra::Log::OutputString)`log:parsedAsN3`

(See RDF::N3::Algebra::Log::ParsedAsN3)`log:semantics`

(See RDF::N3::Algebra::Log::Semantics)

#### RDF Math vocabulary http://www.w3.org/2000/10/swap/math#

`math:absoluteValue`

(See RDF::N3::Algebra::Math::AbsoluteValue)`math:acos`

(See RDF::N3::Algebra::Math::ACos)`math:asin`

(See RDF::N3::Algebra::Math::ASin)`math:atan`

(See RDF::N3::Algebra::Math::ATan)`math:acosh`

(See RDF::N3::Algebra::Math::ACosH)`math:asinh`

(See RDF::N3::Algebra::Math::ASinH)`math:atanh`

(See RDF::N3::Algebra::Math::ATanH)`math:ceiling`

(See RDF::N3::Algebra::Math::Ceiling)`math:cosh`

(See RDF::N3::Algebra::Math::CosH)`math:cos`

(See RDF::N3::Algebra::Math::Cos)`math:difference`

(See RDF::N3::Algebra::Math::Difference)`math:equalTo`

(See RDF::N3::Algebra::Math::EqualTo)`math:exponentiation`

(See RDF::N3::Algebra::Math::Exponentiation)`math:floor`

(See RDF::N3::Algebra::Math::Floor)`math:greaterThan`

(See RDF::N3::Algebra::Math::GreaterThan)`math:lessThan`

(See RDF::N3::Algebra::Math::LessThan)`math:negation`

(See RDF::N3::Algebra::Math::Negation)`math:notEqualTo`

(See RDF::N3::Algebra::Math::NotEqualTo)`math:notGreaterThan`

(See RDF::N3::Algebra::Math::NotGreaterThan)`math:notLessThan`

(See RDF::N3::Algebra::Math::NotLessThan)`math:product`

(See RDF::N3::Algebra::Math::Product)`math:quotient`

(See RDF::N3::Algebra::Math::Quotient)`math:remainder`

(See RDF::N3::Algebra::Math::Remainder)`math:rounded`

(See RDF::N3::Algebra::Math::Rounded)`math:sinh`

(See RDF::N3::Algebra::Math::SinH)`math:sin`

(See RDF::N3::Algebra::Math::Sin)`math:sum`

(See RDF::N3::Algebra::Math::Sum)`math:tanh`

(See RDF::N3::Algebra::Math::TanH)`math:tan`

(See RDF::N3::Algebra::Math::Tan)

#### RDF String vocabulary http://www.w3.org/2000/10/swap/str#

`string:concatenation`

(See RDF::N3::Algebra::Str::Concatenation)`string:contains`

(See RDF::N3::Algebra::Str::Contains)`string:containsIgnoringCase`

(See RDF::N3::Algebra::Str::ContainsIgnoringCase)`string:endsWith`

(See RDF::N3::Algebra::Str::EndsWith)`string:equalIgnoringCase`

(See RDF::N3::Algebra::Str::EqualIgnoringCase)`string:format`

(See RDF::N3::Algebra::Str::Format)`string:greaterThan`

(See RDF::N3::Algebra::Str::GreaterThan)`string:lessThan`

(See RDF::N3::Algebra::Str::LessThan)`string:matches`

(See RDF::N3::Algebra::Str::Matches)`string:notEqualIgnoringCase`

(See RDF::N3::Algebra::Str::NotEqualIgnoringCase)`string:notGreaterThan`

(See RDF::N3::Algebra::Str::NotGreaterThan)`string:notLessThan`

(See RDF::N3::Algebra::Str::NotLessThan)`string:notMatches`

(See RDF::N3::Algebra::Str::NotMatches)`string:replace`

(See RDF::N3::Algebra::Str::Replace)`string:scrape`

(See RDF::N3::Algebra::Str::Scrape)`string:startsWith`

(See RDF::N3::Algebra::Str::StartsWith)

#### RDF Time vocabulary http://www.w3.org/2000/10/swap/time#

`time:dayOfWeek`

(See RDF::N3::Algebra::Time::DayOfWeek)`time:day`

(See RDF::N3::Algebra::Time::Day)`time:gmTime`

(See RDF::N3::Algebra::Time::GmTime)`time:hour`

(See RDF::N3::Algebra::Time::Hour)`time:inSeconds`

(See RDF::N3::Algebra::Time::InSeconds)`time:localTime`

(See RDF::N3::Algebra::Time::LocalTime)`time:minute`

(See RDF::N3::Algebra::Time::Minute)`time:month`

(See RDF::N3::Algebra::Time::Month)`time:second`

(See RDF::N3::Algebra::Time::Second)`time:timeZone`

(See RDF::N3::Algebra::Time::Timezone)`time:year`

(See RDF::N3::Algebra::Time::Year)

## Parser features

### Chaining with `iriPropertyList`

Adds a proposed syntactic extension for *subject embedding* similar to a `blankNodePropertyList`

. An `iriPropertyList`

begins with `[ id _id_`

, instead of a simple `[`

. This sets *id* as the **subject** to be used for the following `propertyList`

. This provides a mechanisms similar to JSON-LD Embedding.

```
@prefix dc: <http://purl.org/dc/terms/>.
@prefix : <http://example.org/nd#>.
:SummerReadingList a :OrderedListOfBooks ;
:toRead (
[id :mobyDick dc:title "Moby Dick"; :setting :WhaleIntestines ]
[
id :jaws
dc:title "Jaws";
:setting :Beach
]
).
```

Note that the *id* used in the `iriPropertyList`

is not delimited by a `;`

### Formulae / Quoted Graphs

N3 Formulae are introduced with the `{ statement-list }`

syntax. A given formula is assigned an `RDF::Node`

instance, which is also used as the graph_name for `RDF::Statement`

instances provided to `RDF::N3::Reader#each_statement`

. For example, the following N3 generates the associated statements:

```
@prefix x: <http://example.org/x-ns/#> .
@prefix log: <http://www.w3.org/2000/10/swap/log#> .
@prefix dc: <http://purl.org/dc/elements/1.1/#> .
{ [ x:firstname "Ora" ] dc:wrote [ dc:title "Moby Dick" ] } a log:falsehood .
```

when turned into an RDF Repository results in the following quads

```
_:form <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2000/10/swap/log#falsehood> .
_:moby <http://purl.org/dc/elements/1.1/#title> "Moby Dick" _:form .
_:ora <http://purl.org/dc/elements/1.1/#wrote> _:moby _:form .
_:ora <http://example.org/x-ns/#firstname> "Ora" _:form .
```

Reasoning uses a Notation3 Algebra, similar to SPARQL S-Expressions. This implementation considers formulae to be patterns, which may be asserted on statements made in the default graph, possibly loaded from a separate file. The logical relationships are reduced to algebraic operators.

### Variables

The latest version of N3 supports only quickVars (e.g., `?x`

). THe former explicit `@forAll`

and `@forSome`

of been removed.
Existential variables are replaced with an allocated `RDF::Node`

instance.

Note that the behavior of both existential and universal variables is not entirely in keeping with the Team Submission, and neither work quite like SPARQL variables. When used in the antecedent part of an implication, universal variables should behave much like SPARQL variables. This area is subject to a fair amount of change.

- Variables, themselves, cannot be part of a solution, which limits the ability to generate updated rules for reasoning.
- Both Existentials and Universals are treated as simple variables, and there is really no preference given based on the order in which they are introduced.

### Query

Formulae are typically used to query the knowledge-base, which is set from the base-formula/default graph. A formula is composed of both constant statements, and variable statements. When running as a query, such as for the antecedent formula in `log:implies`

, statements including either explicit variables or blank nodes are treated as query patterns and are used to query the knowledge base to create a solution set, which is used either prove the formula correct, or create bindings passed to the consequent formula.

Blank nodes associated with rdf:List statements used as part of a built-in are made *non-distinguished* existential variables, and patters containing these variables become optional. If they are not bound as part of the query, the implicitly are bound as the original blank nodes defined within the formula, which allows for both constant list arguments, list arguments that contain variables, or arguments which are variables expanding to lists.

## Dependencies

## Documentation

Full documentation available on RubyDoc.info

### Principle Classes

### Additional vocabularies

## Resources

- RDF.rb
- Distiller
- Documentation
- History
- Notation-3
- Team Submission
- N3 Primer
- N3 Reification
- Turtle
- W3C SWAP Test suite
- W3C Turtle Test suite
- N-Triples

## Author

## Contributing

This repository uses Git Flow to mange development and release activity. All submissions *must* be on a feature branch based on the *develop* branch to ease staging and integration.

- Do your best to adhere to the existing coding conventions and idioms.
- Don't use hard tabs, and don't leave trailing whitespace on any line.
- Do document every method you add using YARD annotations. Read the tutorial or just look at the existing code for examples.
- Don't touch the
`.gemspec`

,`VERSION`

or`AUTHORS`

files. If you need to change them, do so on your private branch only. - Do feel free to add yourself to the
`CREDITS`

file and the corresponding list in the the`README`

. Alphabetical order applies. - Do note that in order for us to merge any non-trivial changes (as a rule of thumb, additions larger than about 15 lines of code), we need an explicit public domain dedication on record from you, which you will be asked to agree to on the first commit to a repo within the organization. Note that the agreement applies to all repos in the Ruby RDF organization.

## License

This is free and unencumbered public domain software. For more information, see https://unlicense.org/ or the accompanying UNLICENSE file.