lv2/atom/atom.ttl

@prefix atom:  <http://lv2plug.in/ns/ext/atom#> .
@prefix lv2:   <http://lv2plug.in/ns/lv2core#> .
@prefix owl:   <http://www.w3.org/2002/07/owl#> .
@prefix rdf:   <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs:  <http://www.w3.org/2000/01/rdf-schema#> .
@prefix ui:    <http://lv2plug.in/ns/extensions/ui#> .
@prefix units: <http://lv2plug.in/ns/extensions/units#> .
@prefix xsd:   <http://www.w3.org/2001/XMLSchema#> .

<http://lv2plug.in/ns/ext/atom>
	a owl:Ontology ;
	rdfs:seeAlso <atom.h> ,
		<util.h> ,
		<forge.h> ,
		<lv2-atom.doap.ttl> ;
	lv2:documentation """

<p>An #Atom is a simple generic data container for holding any type of Plain
Old Data (POD).  An #Atom can contain simple primitive types like integers,
floating point numbers, and strings; as well as structured data like lists and
dictionary-like <q>Objects</q>.  Since Atoms are POD, they can be easily copied
(e.g. using <code>memcpy</code>) anywhere and are suitable for use in real-time
code.</p>

<p>Every atom starts with an LV2_Atom header, followed by the contents.  This
allows code to process atoms without requiring special code for every type of
data.  For example, plugins that mutually understand a type can be used
together in a host that does not understand that type, because the host is only
required to copy atoms, not interpret their contents.  Similarly, plugins (such
as routers, delays, or data structures) can meaningfully process atoms of a
type unknown to them.</p>

<p>Atoms should be used anywhere values of various types must be stored or
transmitted.  The port type #AtomPort can be used to transmit atoms via ports.
An #AtomPort that contains an #Sequence can be used for sample accurate event
communication, such as MIDI, and replaces the earlier event extension.</p>

<h3>Serialisation</h3>

<p>Each Atom type defines a binary format for use at runtime, but also a
serialisation that is natural to express in Turtle format.  Thus, this
specification defines a powerful real-time appropriate data model, as well as a
portable way to serialise any data in that model.  This is particularly useful
for inter-process communication, saving/restoring state, and describing values
in plugin data files.</p>

<h3>Custom Atom Types</h3>

<p>While it is possible to define new Atom types for any binary format, the
standard types defined here are powerful enough to describe almost anything.
Implementations SHOULD build structures out of the types provided here, rather
than define new binary formats (e.g. use #Tuple or #Object rather than
a new C <code>struct</code> type).  Current implementations have support for
serialising all standard types, so new binary formats are an implementation
burden which harms interoperabilty.  In particular, plugins SHOULD NOT expect
UI communication or state saving with custom Atom types to work.  In general,
new Atom types should only be defined where absolutely necessary due to
performance reasons and serialisation is not a concern.</p>
""" .

atom:cType
	a rdf:Property ,
		owl:DatatypeProperty ,
		owl:FunctionalProperty ;
	rdfs:label "C type" ;
	rdfs:domain rdfs:Class ;
	rdfs:range lv2:Symbol ;
	rdfs:comment """The identifier for a C type describing the binary representation of an Atom of this type.""" .

atom:Atom
	a rdfs:Class ;
	rdfs:label "Atom" ;
	atom:cType "LV2_Atom" ;
	lv2:documentation """
<p>Abstract base class for all atoms.  An LV2_Atom has a 32-bit
<code>size</code> and <code>type</code> followed by a body of <code>size</code>
bytes.  Atoms MUST be 64-bit aligned.</p>

<p>All concrete Atom types (subclasses of this class) MUST define a precise
binary layout for their body.</p>

<p>The <code>type</code> field is the URI of an Atom type mapped to an integer.
Implementations SHOULD gracefully pass through, or ignore, atoms with unknown
types.</p>

<p>All atoms are POD by definition except references, which as a special case
have <code>type = 0</code>.  An Atom MUST NOT contain a Reference.  It is safe
to copy any non-reference Atom with a simple <code>memcpy</code>, even if the
implementation does not understand <code>type</code>.  Though this extension
reserves the type 0 for references, the details of reference handling are
currently unspecified.  A future revision of this extension, or a different
extension, may define how to use non-POD data and references.  Implementations
MUST NOT send references to another implementation unless the receiver is
explicitly known to support references (e.g. by supporting a feature).</p>

<p>The atom with both <code>type</code> <em>and</em> <code>size</code> 0 is
<q>null</q>, which is not considered a Reference.</p>
""" .

atom:Chunk
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Chunk of memory" ;
	owl:onDatatype xsd:base64Binary ;
	lv2:documentation """
<p>A chunk of memory with undefined contents.  This type is used to indicate a
certain amount of space is available.  For example, output ports with a
variably sized type are connected to a Chunk so the plugin knows the size of
the buffer available for writing.</p>

<p>The use of a Chunk should be constrained to a local scope, since
interpreting it is impossible without context.  However, if serialised to RDF,
a Chunk may be represented directly as an xsd:base64Binary string, e.g.:</p>

<pre class="turtle-code">
[] eg:someChunk "vu/erQ=="^^xsd:base64Binary .
</pre>
""" .

atom:Number
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Number" .

atom:Int
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "Signed 32-bit integer" ;
	atom:cType "LV2_Atom_Int" ;
	owl:onDatatype xsd:int .

atom:Long
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "Signed 64-bit integer" ;
	atom:cType "LV2_Atom_Long" ;
	owl:onDatatype xsd:long .

atom:Float
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "32-bit floating point number" ;
	atom:cType "LV2_Atom_Float" ;
	owl:onDatatype xsd:float .

atom:Double
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "64-bit floating point number" ;
	atom:cType "LV2_Atom_Double" ;
	owl:onDatatype xsd:double .

atom:Bool
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Boolean" ;
	atom:cType "LV2_Atom_Bool" ;
	owl:onDatatype xsd:boolean ;
	rdfs:comment "An Int where 0 is false and any other value is true." .

atom:String
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "String" ;
	atom:cType "LV2_Atom_String" ;
	owl:onDatatype xsd:string ;
	lv2:documentation """
<p>A UTF-8 encoded string.</p>

<p>The body of an LV2_Atom_String is a C string in UTF-8 encoding, i.e. an
array of bytes (<code>uint8_t</code>) terminated with a NULL byte
(<code>'\\0'</code>).</p>

<p>This type is for free-form strings, but SHOULD NOT be used for typed data or
text in any language.  Use atom:Literal unless translating the string does not
make sense and the string has no meaningful datatype.</p>
""" .

atom:Literal
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "String Literal" ;
	atom:cType "LV2_Atom_Literal" ;
	lv2:documentation """
<p>A UTF-8 encoded string literal, with an optional datatype or language.</p>

<p>This type is compatible with rdfs:Literal and is capable of expressing a
string in any language or a value of any type.  A Literal has a
<code>datatype</code> and <code>lang</code> followed by string data in UTF-8
encoding.  The length of the string data in bytes is <code>size -
sizeof(LV2_Atom_Literal)</code>, including the terminating NULL character.  The
<code>lang</code> field SHOULD be a URI of the form
&lt;http://lexvo.org/id/iso639-3/LANG&gt; or
&lt;http://lexvo.org/id/iso639-1/LANG&gt; where LANG is a 3-character ISO 693-3
language code, or a 2-character ISO 693-1 language code, respectively.</p>

<p>A Literal may have a <code>datatype</code> OR a <code>lang</code>, but never
both.</p>

<p>For example, a Literal can be "Hello" in English:</p>
<pre class="c-code">
void set_to_hello_in_english(LV2_Atom_Literal* lit) {
     lit->atom.type     = map(expand("atom:Literal"));
     lit->atom.size     = 14;
     lit->body.datatype = 0;
     lit->body.lang     = map("http://lexvo.org/id/iso639-1/en");
     memcpy(LV2_ATOM_CONTENTS(LV2_Atom_Literal, lit),
            "Hello",
            sizeof("Hello"));  // Assumes enough space
}
</pre>

<p>or a Turtle string:</p>
<pre class="c-code">
void set_to_turtle_string(LV2_Atom_Literal* lit, const char* ttl) {
     lit->atom.type     = map(expand("atom:Literal"));
     lit->atom.size     = 64;
     lit->body.datatype = map("http://www.w3.org/2008/turtle#turtle");
     lit->body.lang     = 0;
     memcpy(LV2_ATOM_CONTENTS(LV2_Atom_Literal, lit),
            ttl,
            strlen(ttl) + 1);  // Assumes enough space
}
</pre>
""" .

atom:Path
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:URI ;
	owl:onDatatype atom:URI ;
	rdfs:label "File path string" ;
	lv2:documentation """
<p>A local file path.</p>

<p>A Path is a URI reference with only a path component: no scheme, authority,
query, or fragment.  In particular, paths to files in the same bundle may be
cleanly written in Turtle files as a relative URI.  However, implementations
may assume any binary Path (e.g. in an event payload) is a valid file path
which can passed to system functions like fopen() directly, without any
character encoding or escape expansion required.</p>

<p>Any implemenation that creates a Path atom to transmit to another is
responsible for ensuring it is valid.  A Path SHOULD always be absolute, unless
there is some mechanism in place that defines a base path.  Since this is not
the case for plugin instances, effectively any Path sent to or received from a
plugin instance MUST be absolute.</p>
""" .

atom:URI
	a rdfs:Class ,
		rdfs:Datatype ;
	rdfs:subClassOf atom:String ;
	owl:onDatatype xsd:anyURI ;
	rdfs:label "URI string" ;
	lv2:documentation """
<p>A URI string.  This is useful when a URI is needed but mapping is
inappropriate, for example with temporary or relative URIs.  Since the ability
to distinguish URIs from plain strings is often necessary, URIs MUST NOT be
transmitted as atom:String.</p>

<p>This is not strictly a URI, since UTF-8 is allowed.  Escaping and related
issues are the host's responsibility.</p>
""" .

atom:URID
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Integer URID" ;
	atom:cType "LV2_Atom_URID" ;
	lv2:documentation """
<p>An unsigned 32-bit integer mapped from a URI (e.g. with LV2_URID_Map).</p>
""" .

atom:Vector
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Vector" ;
	atom:cType "LV2_Atom_Vector" ;
	lv2:documentation """
<p>A homogeneous series of atom bodies with equivalent type and size.</p>

<p>An LV2_Atom_Vector is a 32-bit <code>child_size</code> and
<code>child_type</code> followed by <code>size / child_size</code> atom
bodies.</p>

<p>For example, an atom:Vector containing 42 elements of type atom:Float:</p>
<pre class="c-code">
struct VectorOf42Floats {
    uint32_t size;        // sizeof(LV2_Atom_Vector_Body) + (42 * sizeof(float);
    uint32_t type;        // map(expand("atom:Vector"))
    uint32_t child_size;  // sizeof(float)
    uint32_t child_type;  // map(expand("atom:Float"))
    float    elems[42];
};
</pre>

<p>Note that it is possible to construct a valid Atom for each element
of the vector, even by an implementation which does not understand
<code>child_type</code>.</p>

<p>If serialised to RDF, a Vector SHOULD have the form:</p>

<pre class="turtle-code">
eg:someVector
     a atom:Vector ;
     atom:childType atom:Int ;
     rdf:value (
         "1"^^xsd:int
         "2"^^xsd:int
         "3"^^xsd:int
         "4"^^xsd:int
     ) .
</pre>
""" .

atom:Tuple
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Tuple" ;
	lv2:documentation """
<p>A series of Atoms with varying <code>type</code> and <code>size</code>.</p>

<p>The body of a Tuple is simply a series of complete atoms, each aligned to
64 bits.</p>

<p>If serialised to RDF, a Tuple SHOULD have the form:</p>

<pre class="turtle-code">
eg:someVector
     a atom:Tuple ;
     rdf:value (
         "1"^^xsd:int
         "3.5"^^xsd:float
         "etc"
     ) .
</pre>

""" .

atom:Property
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Property" ;
	atom:cType "LV2_Atom_Property" ;
	lv2:documentation """
<p>A property of an atom:Object.  An LV2_Atom_Property has a URID
<code>key</code> and <code>context</code>, and an Atom <code>value</code>.
This corresponds to an RDF Property, where the <q>key</q> is the <q>predicate</q>
and the <q>value</q> is the object.</p>

<p>The <code>context</code> field can be used to specify a different context
for each property, where this is useful.  Otherwise, it may be 0.</p>

<p>Properties generally only exist as part of an atom:Object.  Accordingly,
they will typically be represented directly as properties in RDF (see
atom:Object).  If this is not possible, they may be expressed as partial
reified statements, e.g.:</p>

<pre class="turtle-code">
eg:someProperty
    rdf:predicate eg:theKey ;
    rdf:object eg:theValue .
</pre>
""" .

atom:Object
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Object" ;
	atom:cType "LV2_Atom_Object" ;
	lv2:documentation """
<p>An <q>Object</q> is an atom with a set of properties.  This corresponds to
an RDF Resource, and can be thought of as a dictionary with URID keys.</p>

<p>An LV2_Atom_Object body has a uint32_t <code>id</code> and
<code>type</code>, followed by a series of atom:Property bodies
(LV2_Atom_Property_Body).  The LV2_Atom_Object_Body::otype field is equivalent
to a property with key rdf:type, but is included in the structure to allow for
fast dispatching.</p>

<p>Code SHOULD check for objects using lv2_atom_forge_is_object() or
lv2_atom_forge_is_blank() if a forge is available, rather than checking the
atom type directly.  This will correctly handle the deprecated atom:Resource
and atom:Blank types.</p>

<p>When serialised to RDF, an Object is represented as a resource, e.g.:</p>

<pre class="turtle-code">
eg:someObject
    eg:firstPropertyKey "first property value" ;
    eg:secondPropertyKey "first loser" ;
    eg:andSoOn "and so on" .
</pre>
""" .

atom:Resource
	a rdfs:Class ;
	rdfs:subClassOf atom:Object ;
	rdfs:label "Resource" ;
	owl:deprecated "true"^^xsd:boolean ;
	atom:cType "LV2_Atom_Object" ;
	lv2:documentation """
<p>This class is deprecated.  Use atom:Object instead.</p>

<p>An atom:Object where the <code>id</code> field is a URID, i.e. an Object
with a URI.</p>
""" .

atom:Blank
	a rdfs:Class ;
	rdfs:subClassOf atom:Object ;
	rdfs:label "Blank" ;
	owl:deprecated "true"^^xsd:boolean ;
	atom:cType "LV2_Atom_Object" ;
	lv2:documentation """
<p>This class is deprecated.  Use atom:Object with ID 0 instead.</p>

<p>An atom:Object where the LV2_Atom_Object::id is a blank node ID (NOT a URI).
The ID of a Blank is valid only within the context the Blank appears in.  For
ports this is the context of the associated run() call, i.e. all ports share
the same context so outputs can contain IDs that correspond to IDs of blanks in
the input.</p>
""" .

atom:Sound
	a rdfs:Class ;
	rdfs:subClassOf atom:Vector ;
	rdfs:label "Sound" ;
	atom:cType "LV2_Atom_Sound" ;
	lv2:documentation """
<p>An atom:Vector of atom:Float which represents an audio waveform.  The format
is the same as the buffer format for lv2:AudioPort (except the size may be
arbitrary).  An atom:Sound inherently depends on the sample rate, which is
assumed to be known from context.  Because of this, directly serialising an
atom:Sound is probably a bad idea, use a standard format like WAV instead.</p>
""" .

atom:frameTime
	a rdf:Property ,
		owl:DatatypeProperty ,
		owl:FunctionalProperty ;
	rdfs:range xsd:decimal ;
	rdfs:label "frame time" ;
	lv2:documentation """
<p>Time stamp in audio frames.  Typically used for events.</p>
""" .

atom:beatTime
	a rdf:Property ,
		owl:DatatypeProperty ,
		owl:FunctionalProperty ;
	rdfs:range xsd:decimal ;
	rdfs:label "beat time" ;
	lv2:documentation """
<p>Time stamp in beats.  Typically used for events.</p>
""" .

atom:Event
	a rdfs:Class ;
	rdfs:label "Event" ;
	atom:cType "LV2_Atom_Event" ;
	lv2:documentation """
<p>An atom with a time stamp prefix, typically an element of an atom:Sequence.
Note this is not an Atom type.</p>
""" .

atom:Sequence
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Sequence" ;
	atom:cType "LV2_Atom_Sequence" ;
	lv2:documentation """
<p>A sequence of atom:Event, i.e. a series of time-stamped Atoms.</p>

<p>LV2_Atom_Sequence_Body.unit describes the time unit for the contained atoms.
If the unit is known from context (e.g. run() stamps are always audio frames),
this field may be zero.  Otherwise, it SHOULD be either units:frame or
units:beat, in which case ev.time.frames or ev.time.beats is valid,
respectively.</p>

<p>If serialised to RDF, a Sequence has a similar form to atom:Vector, but for
brevity the elements may be assumed to be atom:Event, e.g.:</p>

<pre class="turtle-code">
eg:someSequence
    a atom:Sequence ;
    rdf:value (
        [
            atom:frameTime 1 ;
            rdf:value "901A01"^^midi:MidiEvent
        ] [
            atom:frameTime 3 ;
            rdf:value "902B02"^^midi:MidiEvent
        ]
    ) .
</pre>
""" .

atom:AtomPort
	a rdfs:Class ;
	rdfs:subClassOf lv2:Port ;
	rdfs:label "Atom Port" ;
	lv2:documentation """
<p>A port which contains an atom:Atom.  Ports of this type are connected to an
LV2_Atom with a type specified by atom:bufferType.</p>

<p>Output ports with a variably sized type MUST be initialised by the host
before every run() to an atom:Chunk with size set to the available space.  The
plugin reads this size to know how much space is available for writing.  In all
cases, the plugin MUST write a complete atom (including header) to outputs.
However, to be robust, hosts SHOULD initialise output ports to a safe sentinel
(e.g. the null Atom) before calling run().</p>
""" .

atom:bufferType
	a rdf:Property ,
		owl:ObjectProperty ;
	rdfs:domain atom:AtomPort ;
	rdfs:range rdfs:Class ;
	rdfs:label "buffer type" ;
	lv2:documentation """
<p>Indicates that an AtomPort may be connected to a certain Atom type.  A port
MAY support several buffer types.  The host MUST NOT connect a port to an Atom
with a type not explicitly listed with this property.  The value of this
property MUST be a sub-class of atom:Atom.  For example, an input port that is
connected directly to an LV2_Atom_Double value is described like so:</p>

<pre class="turtle-code">
&lt;plugin&gt;
    lv2:port [
        a lv2:InputPort , atom:AtomPort ;
        atom:bufferType atom:Double ;
    ] .
</pre>

<p>This property only describes the types a port may be <em>directly</em>
connected to.  It says nothing about the expected contents of containers.  For
that, use atom:supports.</p>
""" .

atom:childType
	a rdf:Property ,
		owl:ObjectProperty ;
	rdfs:label "child type" ;
	rdfs:comment "The type of a container's children." .

atom:supports
	a rdf:Property ;
	rdfs:label "supports" ;
	rdfs:range rdfs:Class ;
	lv2:documentation """
<p>Indicates that a particular Atom type is supported.</p>

<p>This property is defined loosely, it may be used to indicate that anything
<q>supports</q> an Atom type, wherever that may be useful.  It applies
<q>recursively</q> where collections are involved.</p>

<p>In particular, this property can be used to describe which event types are
expected by a port.  For example, a port that receives MIDI events is described
like so:</p>

<pre class="turtle-code">
&lt;plugin&gt;
    lv2:port [
        a lv2:InputPort , atom:AtomPort ;
        atom:bufferType atom:Sequence ;
        atom:supports midi:MidiEvent ;
    ] .
</pre>
""" .

atom:eventTransfer
	a ui:PortProtocol ;
	rdfs:label "event transfer" ;
	lv2:documentation """
<p>Transfer of individual events in a port buffer.  Useful as the
<code>format</code> for a LV2UI_Write_Function.</p>

<p>This protocol applies to ports which contain events, usually in an
atom:Sequence.  The host must transfer each individual event to the recipient.
The format of the received data is an LV2_Atom, there is no timestamp
header.</p>
""" .

atom:atomTransfer
	a ui:PortProtocol ;
	rdfs:label "atom transfer" ;
	lv2:documentation """
<p>Transfer of the complete atom in a port buffer.  Useful as the
<code>format</code> for a LV2UI_Write_Function.</p>

<p>This protocol applies to atom ports.  The host must transfer the complete
atom contained in the port, including header.</p>
""" .