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

# LV2 Atom Extension
# Copyright 2007-2011 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 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:release [
		doap:revision "0.1" ;
		doap:created "2011-04-05"
	] ;
	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 format for a typed piece of data, called an
"<a href="#Atom">Atom</a>" (e.g. integers, strings, buffers, data structures,
etc).  Atoms allow LV2 plugins and hosts to communicate, process, serialise,
and store values of any type via a generic mechanism (e.g. LV2 ports, events,
disk, shared memory, network).  Atoms are, with one exception, Plain
Old Data (POD) and may be safely 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>An Atom can be trivially constructed in-place from an
<a href="http://lv2plug.in/ns/ext/event#Event">Event</a> as defined by the
<a href="http://lv2plug.in/ns/ext/event">LV2 Event</a> extension.  In other
words, an Event is simply an Atom with a time stamp header.  Atoms SHOULD
be used anywhere a "value" needs to be stored or communicated, to allow
implementations to be polymorphic and extensible.</p>

<p>Atoms (the start of the LV2_Atom header) MUST be 32-bit aligned.</p>

<p>Atoms can be communicated in many ways.  Since an Atom is the payload of an
Event, an <a href="http://lv2plug.in/ns/ext/event#EventPort">EventPort</a>
can be used for communicating Atoms in realtime with sub-sample time stamp
accuracy.  This extension also defines two port types for connecting directly
to a single Atom: <a href="#ValuePort">ValuePort</a> and <a href="#MessagePort"
>MessagePort</a>, which both have the same buffer format but different
semantics (with respect to how the run() callback interprets the Atom).</p>

<p>This extension requires the host to support the <a
href="http://lv2plug.in/ns/ext/uri-map">LV2 URI Map</a> extension.</p>
""" .

atom:Atom
	a rdfs:Class ;
	rdfs:label "Atom" ;
	lv2:documentation """
<p>Abstract base class for all atoms.  An LV2_Atom has a 16-bit
<code>type</code> and <code>size</code> followed by a <code>body</code> of
<code>size</code> bytes.</p>

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

<p>The <code>type</code> field is the URI of a subclass of Atom mapped to an
integer using the <a href="http://lv2plug.in/ns/ext/uri-map">URI Map</a>
extension's LV2_URI_Map_Feature::uri_to_id() with
<code>map = "http://lv2plug.in/ns/ext/event"</code>.  If a plugin or host
does not understand <code>type</code>, that atom SHOULD be gracefully ignored
(or copied if it does not have type 0).</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, actual specification of how references are used is left
to another extension.</p>
""" .

atom:String
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "String" ;
	lv2:documentation """
<p>A UTF-8 encoded string.</p>

<p>The body of an 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" ;
	lv2:documentation """
<p>A UTF-8 encoded string literal, with an optional language tag or datatype.</p>

<p>This type is compatible with an RDF literal and is capable of expressing a
string in any language, or a value of any type.  An LV2_Atom_Literal has an <a
href="#ID">ID</a> <code>lang</code> and <code>datatype</code> followed by the
string data in UTF-8 encoding.  The length of the string data in bytes is
<code>size - (2 * sizeof(uint32_t))</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>For example, "Hello" in English:</p>
<pre class="c-code">
struct LV2_Atom {
    uint16_t type = uri_to_id(atom:Literal);
    uint16_t size = 14;
}
uint32_t datatype = 0;
uint32_t lang     = uri_to_id("http://lexvo.org/id/term/en");
char     str[]    = "Hello";
</pre>
and French:
<pre class="c-code">
struct LV2_Atom {
    uint16_t type = uri_to_id(atom:Literal);
    uint16_t size = 16;
}
uint32_t datatype = 0;
uint32_t lang     = uri_to_id("http://lexvo.org/id/term/fr");
char     str[]    = "Bonjour";
</pre>
<p>or a Turtle string:</p>
<pre class="c-code">
struct LV2_Atom {
    uint16_t type = uri_to_id(atom:Literal);
    uint16_t size = 64;
}
uint32_t datatype = uri_to_id("http://www.w3.org/2008/turtle#turtle");
uint32_t lang     = 0;
char     str[]    = "&lt;http://example.org/foo&gt; a &lt;http://example.org/Thing&gt; ."
</pre>
""" .

atom:ID
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Integer ID mapped from a URI" ;
	lv2:documentation """
An unsigned 32-bit integer mapped from a URI using the <a
href="http://lv2plug.in/ns/ext/uri-map">URI Map</a> extension's
LV2_URI_Map_Feature::uri_to_id() with <code>map = NULL</code>.
""" .

atom:BlankID
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Integer ID for a blank node" ;
	lv2:documentation """
An unsigned 32-bit integer identifier for a blank node.  A BlankID is only
meaningful within a limited scope (e.g. the Atom in which it appears), and
MUST NOT be used as a global identifier.  In particular, a BlankID is NOT an
ID, and can not be mapped to/from a URI.
""" .

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

<p>An LV2_Atom_Vector is a 16-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 <a
href="#Atom">Atom</a> 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 looks
like this in memory:</p>
<pre class="c-code">
struct LV2_Atom {
    uint16_t type = uri_to_id(atom:Vector);
    uint16_t size = sizeof(LV2_Atom) + sizeof(LV2_Atom_Vector) + (42 * sizeof(float);
}
struct LV2_Vector {
    uint16_t elem_count = 42;
    uint16_t elem_type  = uri_to_id(atom:Float);
}
float elem_00;
float elem_01;
...
float elem_41;
</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>

<p>A Vector header is 64-bits, thus the first element of a Vector is 64-bit
aligned if the Vector itself is 64-bit aligned.</p>
""" .

atom:Tuple
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Tuple" ;
	lv2:documentation """
<p>A sequence of <a href="#Atom">atoms</a> with varying <code>type</code>
and <code>size</code>.</p>

<p>The body of a Tuple is simply a sequence of complete atoms, each aligned to
32 bits.</p>
""" .

atom:Property
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Property of an Object" ;
	lv2:documentation """
A single property of some <a href="#Object">Object</a>.  An
LV2_Atom_Property has an <a href="#ID">ID</a> <code>key</code> and
<a href="#Atom">Atom</a> <code>value</code>.
""" .

atom:Object
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Object" ;
	lv2:documentation """
<p>Abstract base class for an "Object", i.e. an <a href="#Atom">Atom</a> with a
number of <a href="#Property">properties</a>.  An LV2_Object is an unsigned
32-bit integer <code>context</code> and <code>id</code> followed by a sequence
of LV2_Atom_Property .</p>

<p>The <code>context</code> is mapped using the <a
href="http://lv2plug.in/ns/ext/uri-map">URI Map</a> extension's
LV2_URI_Map_Feature::uri_to_id() with <code>map = NULL</code>, and may be 0
(the default context).</p>

<p>Note this is an abstract class, i.e. no Atom can exist with <code>type =
uri_to_id(atom:Object)</code>.  An Object is either a <a
href="#Resource">Resource</a> or a <a href="#Blank">Blank</a>, but the
<code>body</code> always has the same binary format, LV2_Object.  Thus, both
named and anonymous objects can be handled with common code using only a 64-bit
header for both.</p>
""" .

atom:Resource
	a rdfs:Class ;
	rdfs:subClassOf atom:Object ;
	lv2:documentation """
An <a href="#Object">Object</a> where <code>id</code> is the
URI of the resource mapped to an <a href="#ID">ID</a>.
""" .

atom:Blank
	a rdfs:Class ;
	rdfs:subClassOf atom:Object ;
	lv2:documentation """
An <a href="#Object">Object</a> where <code>id</code> is the blank node ID of
the object, which is only meaningful within a certain limited scope
(e.g. the container of the Blank) and MUST NOT be used as a global ID.
In particular, <code>id</code> is NOT an <a href="ID">ID</a>.
""" .

atom:Model
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Model" ;
	lv2:documentation """
A description of a set of <a href="#Object">objects</a>.  In memory, a Model is
simply a sequence of objects.
""" .

atom:Event
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Event" ;
	lv2:documentation """
An atom with a time stamp header prepended, typically for sample accurate
transmission via LV2 ports.  See struct LV2_Atom_Event.
""" .

atom:MidiMessage
	a rdfs:Class ;
	rdfs:label "MIDI Message" ;
	rdfs:subClassOf atom:Atom ;
	lv2:documentation """
<p>A single raw MIDI message.</p>

<p>This is a standard MIDI message, with the following restrictions to ease the
burden on plugin authors:</p>
<ul>
  <li>Running status is not allowed, every message must have its own status
  byte.</li>

  <li>Note On messages with velocity 0 are not allowed.  These messages are
  equivalent to Note Off in standard MIDI streams, but here only proper Note
  Off messages are allowed.</li>

  <li>"Realtime messages" (status bytes 0xF8 to 0xFF) are allowed, but may
  not occur inside other messages like they can in standard MIDI streams.</li>
</ul>
""" .

atom:Bang
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Bang (activity) (size = 0)" .

atom:Byte
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Byte (<code>size = 1</code>)" .

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

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

atom:Bool
	a rdfs:Class ;
	rdfs:subClassOf atom:Atom ;
	rdfs:label "Signed 32-bit integer where 0 is false" .

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

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

atom:blobSupport
	a lv2:Feature ;
	rdfs:label "Blob support" ;
	lv2:documentation """
Support for dynamically allocated blobs.  If a host supports this feature, it
MUST pass a LV2_Feature with <code>URI</code>
http://lv2plug.in/ns/ext/atom#blobSupport and <code>data</code> pointing to a
LV2_Blob_Support.
""" .

atom:AtomPort
	a rdfs:Class ;
	rdfs:subClassOf lv2:Port ;
	rdfs:label "Atom Port" ;
	lv2:documentation """
<p>A port which contains an <a href="#Atom">Atom</a>.  Ports of this type will
be connected to a 32-bit aligned LV2_Atom immediately followed by
<code>size</code> bytes of data.</p>

<p>This is an abstract port type, i.e. a port MUST NOT only be an AtomPort,
but must be a more descriptive type that is a subclass of AtomPort which
defines the port's semantics (typically <a href="#ValuePort">ValuePort</a>
or <a href="#MessagePort">MessagePort</a>).</p>

<p>Before calling a method on the 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 = 0</code> and <code>size = 0</code>).</p>
""" .

atom:ValuePort
	a rdfs:Class ;
	rdfs:subClassOf atom:AtomPort ;
	rdfs:label "Value Port" ;
	lv2:documentation """
An AtomPort that interprets its data as a persistent and time-independent
"value".
<ul>
<li>If a plugin has fixed input values for all ports, 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 V of that ValuePort corresponds to a single set of outputs
for all ports.</li>
<li>If a ValuePort contains a reference then the blob it refers to is
constant; plugin MUST NOT modify the blob in any way.</li>
</ul>
Value ports can be thought of as purely functional ports: if a plugin
callback has only value ports, then the plugin callback is a pure function.
""" .

atom:MessagePort
	a rdfs:Class ;
	rdfs:subClassOf atom:AtomPort ;
	rdfs:label "Message Port" ;
	rdfs:comment """
An AtomPort that "receives", "consumes", "executes", or "sends" its value.
The Atom contained in a MessagePort is considered transient and/or
time-dependent, and is only valid for a single run invocation.  Unlike a
ValuePort, a MessagePort may be used to manipulate internal plugin state.

Intuitively, a MessagePort contains a "message" or "command" or "event"
which is reacted to, NOT a "value" or "signal" (which is computed with).
""" .

atom:EventPort
	a rdfs:Class ;
	rdfs:label "Event port" ;
	rdfs:subClassOf lv2:Port ;
	lv2:documentation """
Ports of this type will be connected to an LV2_Atom_Event_Buffer.  These ports
contain a sequence of atom:Event (i.e. time stamped atoms).  These ports are
used to send and receive atoms in the audio context
(i.e. LV2_Descriptor::run()), and are intended as a simpler, more generic, and
atom compatible successor to <a
href="http://lv2plug.in/ns/ext/event#EventPort">ev:EventPort</a>.
""" .

atom:supports
	a rdf:Property ;
	rdfs:domain lv2:Port ;
	rdfs:range atom:Atom ;
	rdfs:label "supports" ;
	lv2:documentation """
Indicates that a Port supports a certain <a href="#Atom">Atom</a> type.
This is distinct from the port type - e.g. the port type ValuePort can hold
atoms with many different types.  This property is used to describe which
Atom types a Port expects to receive or send.
""" .