This vocabulary defines messages which can be used to access and manipulate properties. It is designed to provide a dynamic control interface for LV2 plugins, but is useful in many contexts.

The main feature of this design is that the messages themselves are described in the same format as the data they work with. In particular, messages can be serialised as a binary Object or in Turtle (or any other RDF serialisation).

The idea behind using a property-based interface for control is to prevent an an explosion of message types. Instead of a custom message for each action, control is achieved via manipulating properties (which are likely already defined for other reasons). Note, however, that this is purely conceptual; there is no requirement that the receiver actually implement a store of resources with properties.

For example, consider an object that can blink. Rather than define a specific interface to control this (e.g. obj.start_blinking(); obj.stop_blinking()), set a blinking property to true or false (e.g. obj.set(blinking, true)) to achieve the desired behaviour. One benefit of this approach is that a persistent state model is available for free: simply serialise the blinking property.

This specification is strictly metadata and does not define any binary mechanism, though it can be completely expressed by standard types in the LV2 Atom extension. Thus, hosts can be expected to be capable of transmitting it between plugins, or between a plugin and its UI, making it a good choice for advanced plugin control.

Reference

ClassesPropertiesInstances

Classes

Ack

Subclass ofResponse
Ack

An acknowledgement that a request has been successfully processed. This is returned as a reply when a specific reply type is not necessary or appropriate.

Copy

Subclass ofRequest
Copy

Copy the patch:subject to patch:destination. After this, patch:destination has the description patch:subject had prior to this request's execution, and patch:subject is unchanged. It is an error if the subject does not exist or the destination already exists. Multiple patch:subject properties may be given if the patch:destination is a container, the semantics of this use case are application defined.

Restriction on subject
owl:minCardinality 1
Restriction on destination
owl:cardinality 1

Delete

Subclass ofRequest
Delete

Request the subject(s) be deleted.

Error

Subclass ofResponse
Error

A response indicating an error processing a request.

Get

Subclass ofRequest
Get

Request a description of the subject.

The detail of the response is not specified, it may be a flat description of all the properties of the subject, or a more expressive description with several subjects. A good choice is a concise bounded description, i.e. a description which recursively includes all properties with blank node values.

The response should have the same patch:subject property as the request, and a patch:body that is a description of that subject. For example:

<get-request>
    a patch:Get ;
    patch:subject <something> .

Could result in:

[]
    a patch:Response ;
    patch:request <get-request> ;
    patch:subject <something> ;
    patch:body [
        eg:name "Something" ;
        eg:ratio 1.6180339887 ;
    ] .

Note the use of blank nodes is not required; the value of patch:body may be the actual resource node. Depending on the transport and syntax used this may be preferable. For example, the same response could be written:

<something>
    eg:name "Something" ;
    eg:ratio 1.6180339887 .

[]
    a patch:Response ;
    patch:request <get-request> ;
    patch:subject <something> ;
    patch:body <something> .

If the patch:subject property is absent, then the Get implicitly applies to the receiver.

Insert

Subclass ofRequest
Insert

Insert the patch:body at patch:subject. If the subject does not exist, it is created. If the subject does already exist, it is added to. This request only adds properties, it never removes them. The user must take care that multiple values are not set for properties which should only have one value.

Restriction on subject
owl:cardinality 1

Move

Subclass ofRequest
Move

Move the patch:subject to patch:destination. After this, patch:destination has the description patch:subject had prior to this request's execution, and patch:subject no longer exists. It is an error if the subject does not exist or the destination already exists.

Restriction on subject
owl:cardinality 1
Restriction on destination
owl:cardinality 1

Patch

Subclass ofRequest
Patch

Add and/or remove properties of the subject.

This method always has at least one patch:subject, and exactly one patch:add and patch:remove property. The value of patch:add and patch:remove are nodes which have the properties to add or remove from the subject(s), respectively. The special value patch:wildcard may be used as the value of a remove property to remove all properties with the given predicate. For example:

[]
    a patch:Patch ;
    patch:subject <something> ;
    patch:add [
        eg:name "New name" ;
        eg:age 42 ;
    ] ;
    patch:remove [
        eg:name "Old name" ;
        eg:age patch:wildcard ;  # Remove all old eg:age properties
    ] .
Restriction on subject
owl:minCardinality 1

Put

Subclass ofRequest
Put

Put the patch:body as the patch:subject. If the subject does not already exist, it is created. If the subject does already exist, the patch:body is considered an updated version of it, and the previous version is replaced.

[]
    a patch:Put ;
    patch:subject <something> ;
    patch:body [
        eg:name "New name" ;
        eg:age 42 ;
    ] .
Restriction on subject
owl:cardinality 1

Request

Subclass ofMessage
In domain ofaccept
In range ofrequest
Request

A request. A request may have a patch:subject property, which indicates which resource the request applies to. The subject may be omitted in contexts where it is implicit (e.g. the recipient is the subject).

Response

Subclass ofMessage
In domain ofrequest
Response

A response to a message.

Set

Subclass ofRequest
In domain ofproperty
value
Set

A compact message for setting one property to a specific value.

This is equivalent to a patch:Patch which removes all pre-existing values for the property before setting the new value. For example:

[]
    a patch:Set ;
    patch:subject <something> ;
    patch:property eg:name ;
    patch:value "New name" .

Which is equivalent to:

[]
    a patch:Patch ;
    patch:subject <something> ;
    patch:add [
        eg:name "New name" ;
    ] ;
    patch:remove [
        eg:name patch:wildcard ;
    ] .
Restriction on property
owl:cardinality 1
Restriction on value
owl:cardinality 1

Properties

accept

DomainRequest
Rangerdfs:Class
accept

An accepted type for a response.

add

TypeObject Property
DomainMessage

body

TypeObject Property
DomainMessage

The body of a message. The details of this property's value depend on the type of message it is a part of.

context

TypeObject Property
DomainMessage

The context of properties in this message. For example, a plugin may have a special context for ephemeral properties which are only relevant during the lifetime of the instance and should not be saved in state. The specific uses for contexts are application specific. However, the context MUST be a URI, and can be interpreted as the ID of a data model where properties should be stored. Implementations MAY have special support for contexts, for example by storing in a quad store or serializing to a format that supports multiple RDF graphs such as TriG.

destination

TypeObject Property
DomainMessage

property

DomainSet
Rangerdf:Property
property

The property for a Set message.

readable

Rangerdf:Property
readable

Indicates that the subject may have a property that can be read via a patch:Get message. See the similar property patch:writable for details.

remove

TypeObject Property
DomainMessage
remove

request

TypeObject Property
DomainResponse
RangeRequest
request

The request this is a response to. This can be used if referring directly to the URI or blank node ID of the request is possible. Otherwise, use patch:sequenceNumber.

sequenceNumber

TypeObject Property
DomainMessage
Rangexsd:int
sequence number

The sequence number of a request or response. This property is used to associate replies with requests when it is not feasible to refer to request URIs with patch:request. A patch:Response with a given sequence number is the reply to the previously send patch:Request with the same sequence number. The special sequence number 0 means no reply is desired.

subject

TypeObject Property
DomainMessage

The subject this message applies to.

value

DomainSet
Rangerdf:Property
value

The value of a property in a patch:Set message.

writable

Rangerdf:Property
writable

Indicates that subject may have a property that can be written via a patch message. This is used to list supported properties, e.g. so user interfaces can present appropriate controls. For example:

@prefix eg:   <http://example.org/> .
@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

eg:title
    a rdf:Property ;
    rdfs:label "title" ;
    rdfs:range xsd:string .

eg:plugin
    patch:writable eg:title .

Instances

wildcard

Typerdfs:Resource

A wildcard which matches any resource. This makes it possible to describe the removal of all values for a given property.

History

Version 2.6 (2019-02-03)
  • Add patch:accept property.
  • Add patch:context property.
Version 2.4 (2015-04-07)
  • Define patch:Get with no subject to implicitly apply to reciever. This can be used by UIs to get an initial description of a plugin.
  • Add patch:Copy method.
Version 2.2 (2014-08-08)
  • Add patch:sequenceNumber for associating replies with requests.
Version 2.0 (2013-01-10)
  • Make patch:Set a compact message for setting one property.
  • Add patch:readable and patch:writable for describing available properties.
Version 1.0 (2012-04-17)
  • Initial release.