manifestation. Item is "a single exemplar of a manifestation. The entity defined as item is a concrete entity." Each copy of the 1996 pressings of that 1996 recording is an item. When we say, "Both copies of the London Philharmonic's 1996 performance of the Ninth are checked out of my local library," we are generally referring to items. Group 1 entities are not strictly hierarchical, because entities do not always inherit properties from other entities. Despite initial positive assessments of FRBR clarifying the thoughts around the conceptual underpinnings of works, there has been later disagreement about what the Group 1 entities actually mean. The distinction between Works and Expressions is also unclear in many cases. Relationships In addition to the relationships between Group 1 and Groups 2 and 3 discussed above, there are many additional relationships covering such things as digitized editions of a work to the original text, and derivative works such as adaptations and parodies, or new texts which are critical evaluations of a pre-existing text. FRBR is built upon relationships between and among entities. "Relationships serve as the vehicle for depicting the link between one entity and another, and thus as the means of assisting the user to ‘navigate’ the universe that is represented in a bibliography, catalogue, or bibliographic database." Examples of relationship types include, but are not limited to: Equivalence relationships Equivalence relationships exist between exact copies of the same manifestation of a work or between an original item and reproductions of it, so long as the intellectual content and authorship are preserved. Examples include reproductions such as copies, issues, facsimiles and reprints, photocopies, and microfilms. Derivative relationships Derivative relationships exist between a bibliographic work and a modification based on the work. Examples include: Editions, versions, translations, summaries, abstracts, and digests Adaptations that become new works but are based on old works Genre changes New works based on the style or thematic content of the work Descriptive relationships Descriptive relationships exist between a bibliographic entity and a description, criticism, evaluation, or review of that entity, such as between a work and a book review describing it. Descriptive relationships also includes annotated editions, casebooks, commentaries, and critiques of an existing work. See also BIBFRAME Functional Requirements for Authority Data (FRAD) FRSAD FRBRoo IFLA Library Reference Model International Cataloguing Principles (ICP) Resource Description and Access (RDA) Paris Principles (PP) References Further reading Karen Coyle, FRBR Before and