RELs can be used as standalone expressions (i.e. metadata usable for search, compatibility tracking) or within a DRM system.
Although RELs may be processed directly, they can also be encountered when embedded as metadata within other documents, such as eBooks, image, audio or video files.
Some software bill of materials (SBOM) products, such as Software Package Data Exchange (SPDX) do not use a REL but instead limit potential licences to a set of well-known licences, expressed through their local controlled vocabulary of SPDX ID.
However this still requires human intervention to check these licences for acceptability and for their effects when combined: the non-REL SBOM product cannot do this itself.
Such a model[17] expresses itself as lists of: The REL defines sets of members for each of these three groups, and the permitted relations between them.
Increasing interest in mashups and collaborative projects creates a demand for combining content, and in licensing technologies that can support this.
An obvious example of this are the Creative Commons licenses, where a family of licences are all defined in terms of the same REL.
A regular problem with semantic translation between schemas (such as RELs) is in making sure that the meanings of terms are identical.
Although the semantic web is beginning to use ontology tools such as OWL to describe meaning, the current state of the art for REL is less advanced than this.
Simpler processing, and the potential for expensive litigation otherwise, means that the semantics of RELs must be clearly identical, not just inferred to be so through a reasoner.
Not all RELs support all classes though: some ignore Jurisdiction or even End-user, according to the needs of the market they were developed for.
Some RELs take the "Everything not permitted is forbidden" approach, others (such as ccREL) use the Berne Convention as their baseline.