persist
type: Specification
name: LV2 Persist
developer: Leonard Ritter
maintainer: David Robillard
comment: This extension provides a mechanism for plugins to save and restore state across instances, allowing hosts to save configuration/state/data with a project or fully clone a plugin instance (including internal state). The motivating idea behind this extension is that a plugin instance's state is entirely represented by port values and a single key/value dictionary. This makes state well-defined and easily manageable by hosts. Keys are URIs, avoiding conflicts and allowing the same dictionary to be used to store plugin state in any context. Values are typed tagged (by URI mapped integers), but otherwise are simple binary blobs. This extension defines plugin instance state and provides a mechanism for saving/restoring it, but otherwise makes no restrictions on how a plugin works with state. For example, other extensions may define dynamic ways to control plugin state at runtime. The idea is that all plugin state can be represented with a single (conceptual) dictionary. This state representation is tried-and-true, universal, and works well with many existing technologies. Accordingly, plugins/extensions that deal with instance state in any way SHOULD represent it in a way compatible with this extension, i.e. URI keys with URI-typed values. Similarly, plugins SHOULD NOT use any other mechanism to store/restore state; this will cause serious problems, don't do it! Note that you can store values of any format whatsoever, so if you have an existing state representation to use (e.g. XML), simply store it as a single value under some key. Files may be persisted using this extension in conjunction with the LV2 Files extension. Instance state as defined by this extension is RDF compatible, allowing for simple and seamless integration with existing technology (LV2 or otherwise). An obvious benefit of this is that plugin state can be elegantly described in Turtle files; the persist:instanceState predicate is provided for this purpose. RDF compatibility is also convenient since LV2…

Plugin Instance State
type: Class
comment: This class is used to express a plugin instance's state in RDF. The key/value properties of the instance form the predicate/object (respectively) of triples with a persist:InstanceState as the subject (see persist:instanceState for an example). This may be used wherever it is useful to express a plugin instance's state in RDF (e.g. for serialisation, storing in a model, or transmitting over a network). Note that this class is provided because it may be useful for hosts, plugins, or extensions that work with instance state, but its use is not required to support the LV2 Persist extension.

instanceState
type: Property
range: Plugin Instance State
comment: Predicate to relate a plugin instance to an InstanceState. This may be used wherever the state of a particular plugin instance needs to be represented. Note that the domain of this property is unspecified, since LV2 does not define any RDF class for plugin instance. This predicate may be used wherever it makes sense to do so, e.g.: @prefix eg: <http://example.org/> . <plugininstance> persist:instanceState [ eg:somekey "some value" ; eg:someotherkey "some other value" ; eg:favouritenumber 2 . ] Note that this property is provided because it may be useful for hosts, plugins, or extensions that work with instance state, but its use is not required to support the LV2 Persist extension.