path: root/lv2/ns/ext/atom/atom.ttl

# LV2 Atom Extension
# Copyright 2007-2012 David Robillard <d@drobilla.net>
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

@prefix atom: <http://lv2plug.in/ns/ext/atom#> .
@prefix doap: <http://usefulinc.com/ns/doap#> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@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 xsd:  <http://www.w3.org/2001/XMLSchema#> .

<http://lv2plug.in/ns/ext/atom>
	a lv2:Specification ;
	doap:name "LV2 Atom" ;
	doap:shortdesc "A generic value container and several data types." ;
	doap:license <http://opensource.org/licenses/isc> ;
	rdfs:seeAlso <atom-helpers.h> ,
		<forge.h> ;
	doap:release [
		doap:revision "0.4" ;
		doap:created "2012-02-07"
	] ;
	doap:maintainer [
		a foaf:Person ;
		foaf:name "David Robillard" ;
		foaf:homepage <http://drobilla.net/> ;
		rdfs:seeAlso <http://drobilla.net/drobilla.rdf>
	] ;
	lv2:documentation """
<p>This extension defines a generic container for data, called an <q>Atom</q>,
and several basic Atom types which can be used to express structured data.
Atoms allow LV2 plugins and hosts to communicate, process, serialise, and store
values of any type via a generic mechanism (e.g. ports, files, networks,
ringbuffers, etc.).  Atoms are, with one exception, Plain Old Data (POD) which
may safely be copied (e.g. with a simple call to <code>memcpy</code>).</p>

<p>Since Atom communication can be implemented generically, plugins that
understand some type can be used together in a host that does not understand
that type, and plugins (e.g. routers, delays) can process atoms of unknown
type.</p>

<p>Atoms can and should be used anywhere values of various types must be stored
or transmitted.  This extension defines port types, atom:ValuePort and
atom:MessagePort, which are connected to an Atom.  The atom:Sequence type in
conjunction with atom:MessagePort is intended to replace the <a
href="http://lv2plug.in/ns/ext/event">LV2 event</a> extension.</p>

<p>The types defined in this extension should be powerful enough to express
almost any structure.  Implementers SHOULD build structures out of the types
provided here, rather than define new binary formats (e.g. use atom:Object
rather than a new C <code>struct</code> type).  New binary formats are an
implementation burden which harms interoperabilty, and should only be defined
where absolutely necessary.</p>

<p>Implementing this extension requires a facility for mapping URIs to
integers, such as the <a href="http://lv2plug.in/ns/ext/urid">LV2 URID</a>
extension.</p>
""" .

atom:cType
	a rdf:Property ,
		owl:DatatypeProperty ;
	rdfs:label "C type" ;
	rdfs:domain rdfs:Class ;
	rdfs:range xsd:string ;
	rdfs:comment """
The identifier for a C type describing the in-memory representation of
an instance of this class.
""" .

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>type</code> and <code>size</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 ignore, or pass through, 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).  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:Bang
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Bang" ;
    rdfs:comment "Generic activity or trigger, with no body." .

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

atom:Int32
	a rdfs:Class ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "Signed 32-bit integer" ;
	atom:cType "LV2_Atom_Int32" .

atom:Int64
	a rdfs:Class ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "Signed 64-bit integer" ;
	atom:cType "LV2_Atom_Int64" .

atom:Float
	a rdfs:Class ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "32-bit IEEE-754 floating point number" ;
	atom:cType "LV2_Atom_Float" .

atom:Double
	a rdfs:Class ;
	rdfs:subClassOf atom:Number ;
	rdfs:label "64-bit IEEE-754 floating point number" ;
	atom:cType "LV2_Atom_Double" .

atom:Bool
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Boolean" ;
	atom:cType "LV2_Atom_Bool" ;
	rdfs:comment "An Int32 where 0 is false and any other value is true." .

atom:String
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "String" ;
	atom:cType "LV2_Atom_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 can be used for free-form strings, but in most cases it is better to
use atom:Literal since this supports a language tag or datatype.  Implementations
SHOULD NOT use atom:String 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 rdf: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/term/LANG&gt; where LANG is an <a
href="http://www.loc.gov/standards/iso639-2/">ISO 693-2</a> or <a
href="http://www.loc.gov/standards/iso639-2/">ISO 693-3</a> language code.</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->datatype  = 0;
     lit->lang      = map("http://lexvo.org/id/term/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->datatype  = map("http://www.w3.org/2008/turtle#turtle");
     lit->lang      = 0;
     memcpy(LV2_ATOM_CONTENTS(LV2_Atom_Literal, lit),
            ttl,
            strlen(ttl) + 1);  // Assumes enough space
}
</pre>
""" .

atom:URID
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Integer ID mapped from a URI" ;
	atom:cType "LV2_Atom_ID" ;
	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>elem_count</code> and
<code>elem_type</code> followed by <code>elem_count</code> atom bodies of type
<code>elem_type</code>.  The element type must be a fixed size atom:Atom type,
i.e. the size of each element is the vector's <code>size /
elem_count</code>.</p>

<p>For example, an atom:Vector containing 42 elements of type atom:Float:</p>
<pre class="c-code">
struct VectorOf42Floats {
    uint32_t type;        // map(expand("atom:Vector"))
    uint32_t size;        // sizeof(LV2_Atom_Vector) + (42 * sizeof(float);
    uint32_t elem_count;  // 42
    uint32_t elem_type;   // map(expand("atom:Float"))
    float    elems[32];
};
</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>elem_type</code>.</p>
""" .

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>
""" .

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>
""" .

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 has a uint32_t <code>id</code> and uint32_t
<code>type</code>, followed by a series of atom:Property bodies (without
headers, i.e. LV2_Atom_Property_Body).  The LV2_Atom_Object::type field is
semantically equivalent to a property with key rdf:type, but is included in the
structure to allow for fast dispatch.</p>

<p>This is an abstract Atom type, an Object is always either a atom:Resource
or a atom:Blank.</p>
""" .

atom:Resource
	a rdfs:Class ;
	rdfs:subClassOf atom:Object ;
	rdfs:label "Resource" ;
	atom:cType "LV2_Atom_Object" ;
	lv2:documentation """
<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" ;
	atom:cType "LV2_Atom_Object" ;
	lv2:documentation """
<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:Event
	a rdfs:Class ;
	rdfs:label "Event" ;
	atom:cType "LV2_Atom_Event" ;
	lv2:documentation """
<p>An atom with a time stamp header prepended, 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>
""" .

atom:AtomPort
	a rdfs:Class ;
	rdfs:subClassOf lv2:Port ;
	rdfs:label "Atom Port" ;
	lv2:documentation """
<p>A port which contains an lv2:Atom.  Ports of this type will be connected to
a 64-bit aligned LV2_Atom immediately followed by <code>size</code> bytes of
data.</p>

<p>This is an abstract port type with incomplete semantics which can not be
used directly as a port type.  Atom ports should be either a atom:ValuePort or
a atom:MessagePort.</p>

<p>Before calling a method on a plugin that writes to an AtomPort output, the
host MUST set the size of the Atom in that output to the amount of available
memory immediately following the Atom header.  The plugin MUST write a valid
Atom to that port; leaving it untouched is illegal.  If there is no reasonable
value to write to the port, the plugin MUST write null (the Atom with both
<code>type</code> and <code>size</code> 0).</p>
""" .

atom:ValuePort
	a rdfs:Class ;
	rdfs:subClassOf atom:AtomPort ;
	rdfs:label "Value Port" ;
	lv2:documentation """

<p>An AtomPort that contains a persistent <em>value</em>.  A <q>value</q> is
time-independent and may be used numerous times.  A ValuePort is <q>pure</q> in
the sense that it may affect output but MUST NOT affect persistent plugin state
in any externally visible way.</p>

<ul>
<li>If a plugin has fixed values for all inputs, all ValuePort outputs are also
fixed regardless of the number of times the plugin is run.</li>

<li>If a plugin has fixed input values for all ports except a ValuePort, each
value of that port corresponds to a single set of values for all
ValuePort outputs.</li>

<li>If the plugin saves state other than port values (e.g. using the <a
href="http://lv2plug.in/ns/ext/state">LV2 State</a> extension), changing only
the value of a ValuePort input MUST NOT change that state.  In other words,
value port changes MUST NOT trigger a state change that requires a save.</li>
</ul>

<p>Value ports are essentially purely functional ports: if a plugin has only
value ports, that plugin is purely functional.  Hosts may elect to cache output
and avoid calling run() if the output is already known according to these
rules.</p>
""" .

atom:MessagePort
	a rdfs:Class ;
	rdfs:subClassOf atom:AtomPort ;
	rdfs:label "Message Port" ;
	lv2:documentation """
<p>An AtomPort that contains transient data which is <em>consumed</em> or
<em>sent</em>.  The Atom contained in a MessagePort is time-dependent and only
valid for a single run invocation.  Unlike a ValuePort, a MessagePort may be
used to manipulate internal plugin state.</p>

<p>Intuitively, a MessagePort contains a <q>message</q> or <q>event</q> which
is reacted to <em>once</em> (not a <q>value</q> which is computed with any
number of times).</p>
""" .

atom:bufferType
	a rdf:Property ;
	rdfs:domain atom:AtomPort ;
	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:ValuePort ;
        atom:bufferType atom:Double ;
    ] .
</pre>

<p>Note this property only indicates the atom types a port may be directly
connected to, it is not <q>recursive</q>.  If a port can be connected to a
collection, use atom:supports to indicate which element types are understood.
If a port supports heterogeneous collections (collections that can contain
several types of elements at once), implementations MUST gracefully handle any
types that are present in the collection, even if those types are not
explicitly supported.</p>
""" .

atom:supports
	a rdf:Property ;
	rdfs:label "supports" ;
	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
supported 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:MessagePort ;
        atom:bufferType atom:Sequence ;
        atom:supports midi:MidiEvent ;
    ] .
</pre>
""" .