README
¶
go-rdfjs
Go implementation of the RDF data model
This is a zero-dependency module implementing the RDF data model. It's a faithful and idiomatic adaptation of the RDFJS JSON-based interface and it comes with RDFJS-compatible JSON marshalers and unmarshalers for easy interop with JavaScript libraries like n3.js, jsonld.js, and graphy.js.
Terms
The five term types are the structs NamedNode, BlankNode, Literal, DefaultGraph, and Variable. They all satisfy the Term interface:
type Term interface {
String() string
TermType() string
Value() string
Equal(term Term) bool
MarshalJSON() ([]byte, error)
UnmarshalJSON(data []byte) error
}
Named nodes, blank nodes, and variables all have single string value and can be created with the constructors:
NewNamedNode(value string) *NamedNode
NewBlankNode(value string) *BlankNode
NewVariable(value string) *Variable
It's up to the user to validate that named node values are valid IRIs. Per the RDFJS spec, blank node values should not begin with _:, and variable values should not begin with ?.
Default graphs have no value - the Value() string method always returns the empty string, and the type DefaultGraph is just struct{}. There is a "default default graph" value var Default *DefaultGraph that is recommended for most purposes, although new default graphs can also be created with the constructor:
NewDefaultGraph() *DefaultGraph
Literals have a string value, a string language, and a named node datatype, which may be nil (interpreted as the default datatype of xsd:string). A literal can be created with the constructor:
NewLiteral(value, language string, datatype *NamedNode) *Literal
If the given datatype does not have a value of rdf:langString, then the resulting *Literal will have no langauge, even if one is passed. You can use the exported var RDFLangString *NamedNode value to avoid repeatedly constructing an rdf:langString term.
The term structs do not have internal term type fields - the TermType() string method is a constant function on each struct type. This is done to save memory.
Unmarshal generic terms
Each of the term structs implements MarshalJSON and UnmarshalJSON; however it is often necessary to unmarshal a term without knowing its type in advance:
UnmarshalTerm(data []byte) (Term, error)
Serialize and parse strings
Terms also implement a .String() string method that return their N-Quads term representation (e.g. "example"^^<http://example.com>). The ParseTerm(s: string): Term function parses terms back from this format.
Quads
type Quad [4]Term
Quads are represented interally as 4-tuples of Term interfaces. This was chosen instead of a struct type to support advanced uses like arithmetic or permutations of term positions. Quad terms can be accessed by name with the .Subject(): Term, .Predicate(): Term, .Object(): Term, and .Graph(): Term methods.
Quads also implement MarshalJSON and UnmarshalJSON, which serialize to and from the RDFJS object representation of quads ({"subject": { }, ...}). Internally, Quad.UnmarshalJSON calls the generic UnmarshalTerm for each of its components.
A new quad can be created with the constructor:
NewQuad(subject, predicate, object, graph Term) *Quad
The user is responsible for checking that the terms of a quad are valid for their positions (no literals as subjects, etc). If graph is nil, the "default default graph" var Default *DefaultGraph will be used.
Serialize and parse strings
Quads also have a .String() string method that returns the N-Quads representation of the quad, including a trailing period, but not including a newline. ParseQuad(s: string): *Quad parses a quad back from this format.
You can also parse a slice of quads out of an io.Reader using ReadQuads(input io.Reader) ([]*Quad, error).
Documentation
¶
Index ¶
- Constants
- Variables
- type BlankNode
- type DefaultGraph
- type Literal
- func (node *Literal) Datatype() Term
- func (node *Literal) Equal(term Term) bool
- func (node *Literal) Language() string
- func (node *Literal) MarshalJSON() ([]byte, error)
- func (node *Literal) String() string
- func (node *Literal) TermType() string
- func (node *Literal) UnmarshalJSON(data []byte) error
- func (node *Literal) Value() string
- type NamedNode
- type Quad
- type Term
- type TermLiteral
- type Variable
Constants ¶
const BlankNodeType = "BlankNode"
BlankNodeType is the TermType blank nodes
const DefaultGraphType = "DefaultGraph"
DefaultGraphType is the TermType for default graphs
const LiteralType = "Literal"
LiteralType is the TermType literals
const NamedNodeType = "NamedNode"
NamedNodeType is the TermType for IRIs
const VariableType = "Variable"
VariableType is the TermType for variables
Variables ¶
var Default = &DefaultGraph{}
Default is the default default graph
var ErrParseTerm = errors.New("Error parsing term")
ErrParseTerm indicates that a string could not parse into a term
var ErrTermType = errors.New("Mismatching term types")
ErrTermType indicates an unexpected or mismatching term types
var RDFLangString = &NamedNode{"http://www.w3.org/1999/02/22-rdf-syntax-ns#langString"}
RDFLangString is the datatype for language-tagged literals
var XSDString = &NamedNode{"http://www.w3.org/2001/XMLSchema#string"}
XSDString is the default datatype for literals
Functions ¶
This section is empty.
Types ¶
type BlankNode ¶ added in v0.2.0
type BlankNode struct {
// contains filtered or unexported fields
}
A BlankNode is labelled blank node
func NewBlankNode ¶ added in v0.2.0
NewBlankNode creates a new blank node
func (*BlankNode) MarshalJSON ¶ added in v0.2.0
MarshalJSON marshals the blank node into a byte slice
func (*BlankNode) UnmarshalJSON ¶ added in v0.2.0
UnmarshalJSON umarshals a byte slice into the blank node
type DefaultGraph ¶ added in v0.2.0
type DefaultGraph struct{}
DefaultGraph is the default graph term
func NewDefaultGraph ¶ added in v0.2.0
func NewDefaultGraph() *DefaultGraph
NewDefaultGraph creates a new default graph
func (*DefaultGraph) Equal ¶ added in v0.2.0
func (node *DefaultGraph) Equal(term Term) bool
Equal checks for functional equivalence of terms
func (*DefaultGraph) MarshalJSON ¶ added in v0.2.0
func (node *DefaultGraph) MarshalJSON() ([]byte, error)
MarshalJSON marshals the literal into a byte slice
func (*DefaultGraph) String ¶ added in v0.2.1
func (node *DefaultGraph) String() string
func (*DefaultGraph) TermType ¶ added in v0.2.0
func (node *DefaultGraph) TermType() string
TermType of a default graph is "DefaultGraph"
func (*DefaultGraph) UnmarshalJSON ¶ added in v0.2.0
func (node *DefaultGraph) UnmarshalJSON(data []byte) error
UnmarshalJSON umarshals a byte slice into the blank node
func (*DefaultGraph) Value ¶ added in v0.2.0
func (node *DefaultGraph) Value() string
Value of a DefaultGraph is the empty string
type Literal ¶ added in v0.2.0
type Literal struct {
// contains filtered or unexported fields
}
A Literal is literal term
func NewLiteral ¶ added in v0.2.0
NewLiteral creates a new literal
func (*Literal) MarshalJSON ¶ added in v0.2.0
MarshalJSON marshals the literal into a byte slice
func (*Literal) UnmarshalJSON ¶ added in v0.2.0
UnmarshalJSON umarshals a byte slice into the literal
type NamedNode ¶ added in v0.2.0
type NamedNode struct {
// contains filtered or unexported fields
}
A NamedNode is an IRI term
func NewNamedNode ¶ added in v0.2.0
NewNamedNode creates a new IRI
func (*NamedNode) MarshalJSON ¶ added in v0.2.0
MarshalJSON marshals the named node into a byte slice
func (*NamedNode) UnmarshalJSON ¶ added in v0.2.0
UnmarshalJSON umarshals a byte slice into the named node
type Quad ¶
type Quad [4]Term
A Quad is a 4-tuple of terms
func ReadQuads ¶ added in v0.3.3
ReadQuads parses an io.Reader of serialize n-quads into a slice of *Quads
func (*Quad) MarshalJSON ¶ added in v0.2.0
MarshalJSON marshals a quad into a byte slice
func (*Quad) UnmarshalJSON ¶ added in v0.2.0
UnmarshalJSON unmarshals a byte slice into a quad
type Term ¶
type Term interface {
String() string
TermType() string
Value() string
Equal(term Term) bool
MarshalJSON() ([]byte, error)
UnmarshalJSON(data []byte) error
}
Term is the interface that all terms satisfy
func UnmarshalTerm ¶
UnmarshalTerm unmarshals a byte slice into a Term
func UnmarshalTerms ¶ added in v0.3.1
UnmarshalTerms unmarshals a JSON array of RDFJS terms into a slice of rdf.Terms
type TermLiteral ¶ added in v0.2.0
TermLiteral is an interface for literal terms. This is only used in the Equal() method of the Literal struct. You shouldn't have to worry about this unless you're going to use external implementations of Term, in which case you need to make sure that literal terms implement this interface.
type Variable ¶ added in v0.2.0
type Variable struct {
// contains filtered or unexported fields
}
A Variable is labelled variable
func NewVariable ¶ added in v0.2.0
NewVariable creates a new variable
func (*Variable) MarshalJSON ¶ added in v0.2.0
MarshalJSON marshals the variable into a byte slice
func (*Variable) UnmarshalJSON ¶ added in v0.2.0
UnmarshalJSON umarshals a byte slice into the variable
Source Files