Extension – Grouping

Grouping is about collecting a set of entities in the model and giving it an identity. The Source is a form of grouping that collects a set of Flows that share the properties defined by the Source. The grouping in this section is more about grouping entities that have a common purpose and are intended to be used together.

Some common examples of grouping are: * Grouping Sources or Flows that share a Time Context and are therefore synchronised. For example, an audio, video and subtitle group which constitutes a TV programme. * Grouping of ISOs or sets of time-coincident audio assets related to a recording session. * Grouping of tracks that make up a media file.

There are a number of aspects that need to be considered when defining a group and its members, such as: * Define a group identifier that is unique. * Define a locally unique label for each member of the group. This label along with the group identifier is used to refer to a group member. * Define how a group member references the entity it represents. For example, by using a Source ID to refer to a Source, or a track index to refer to a track in a media file. * Define whether the group members are ordered or not. * Define how the group relates to entities such as Source and Flow. For example, if a group defines the members of a multi-channel audio Source then it is necessary to define how and when the group is used when recording an ancestry relationship for this content.