Releases and Resources such as Sound Recordings do not exist in isolation. Increasingly recordings make use of other recordings and multiple Releases are created from a single recording project or studio session.

The NewReleaseMessage has always been able to express some of these relationships, but ERN 4.2 adds further links.

In the various Resource composites (e.g. SoundRecording), the following links can be expressed:

To link a Resource to a Release other than the Resource-Release expressed though the NewReleaseMessage, can be expressed with the RelatedRelease composite, whereas the RelatedResource composite is able to allow communicating relationships between different sound recordings, e.g. whether one is a sample of the other, whether one is a cover version of the other etc.

For example, when describing The Beatles’ Get Back as part of a “best of album”, a record company may wish include the information that the same recording is also part of the album “Let it Be” and that there is cover version of the same recording with the ISRC US-UMG-000016-2:

<SoundRecording>
	<ResourceReference>A1</ResourceReference>
	<Type>MusicalWorkSoundRecording</Type>
	<ResourceId>
		<ISRC>GBAYE0900783</ISRC>
	</ResourceId>
	<DisplayTitleText>Get Back</DisplayTitleText>
	<DisplayTitle>
		<TitleText>Get Back</TitleText>
	</DisplayTitle>
	<DisplayArtistName>The Beatles</DisplayArtistName>
	<DisplayArtist>
		<ArtistPartyReference>P1</ArtistPartyReference>
		<DisplayArtistRole>Artist</DisplayArtistRole>
	</DisplayArtist>
	<Duration>PT0S</Duration>
	<ParentalWarningType>NoAdviceAvailable</ParentalWarningType>


	<RelatedRelease>
		<!-- This recording also appeared on the album "Let it Be" --> 
		<ReleaseRelationshipType>HasContentFrom</ReleaseRelationshipType>
		<ReleaseId>
			<ICPN>094638247210</ICPN>
		</ReleaseId>
		<DisplayTitle>
			<TitleText>Let it Be</TitleText>
		</DisplayTitle>
	</RelatedRelease>


	<RelatedResource>
		<!-- A cover version of "Get Back" was recorded by Billy Preston --> 
		<ResourceRelationshipType>IsCoveredBy</ResourceRelationshipType>
		<ResourceId>
			<ISRC>USUMG0000162</ISRC>
		</ResourceId>
	</RelatedResource>


</SoundRecording>


In addition, it is possible to split a SoundRecording into several chapters, something particularly useful for audio books. This can be done using the AudioChapterReference element; it points to a Chapter composite in the same NewReleaseMessage.

The RelatedRelease and RelatedResource composites can also be used, in the same way for Releases and TrackReleases, especially useful for stating that a Release is an extended version of another Release, that a Release is a digital equivalent to a physical Release, or that a Release – typically a TrackRelease -- contains content from a specific Sound Recording.

Arguably the most important element for a Release or TrackRelease is the one that lists the Sound Recordings (or other Resources) that the Release or TrackRelease contains. This is implemented using the following ID/IDREF pointers the ReleaseResourceReference (for TrackReleases) and ReleaseResourceReference within the ResourceGroup/ResourceGroupContentItem. (for album Releases).

The Release composites also allow these links to be communicated: