ISO IEC TS 22424-2:2020 pdf download – Digital publishing – EPUB3 preservation
Options 2 and 3 are based on the idea that there are two independent specifications, the core EPUB specification (currently version 3.2), and a container specification (this document). This allows the two communities (EPUB and digital archivists) to cooperate without putting unnecessary constraints on each other. Both specifications are independent from one another, which makes it easier to manage them. From a technical point of view, the main strength of the second option is that METS containers are almost universally accepted in long-term preservation applications. One reason for the popularity of the standard is that it is flexible – it is possible to embed any descriptive or administrative metadata into a METS document. Whatever mandatory metadata will be agreed upon by the producer and the OAIS archive, METS can be used as a container. The option of using some other container standard than METS or EPUB is not examined in this document. METS is used due to its technical features and popularity among long-term preservation application vendors as well as libraries, archives, and museums. If and when other options emerge in the future, it is possible to extend this document to support other container standards as well. The main weakness of METS approach is that currently very few publishers support it. Unless production processes change radically, a common solution will be to submit e-books in EPUB format as such, with accompanying ONIX metadata. In this approach, the producer (which can be the OAIS archive) creates the METS SIP during pre-ingest, using the data and metadata delivered by the publisher. The publisher does not need to know METS, but EPUB documents themselves and the accompanying metadata should meet the requirements made in the submission agreement.
This document requires that each SIP shall have a METS document with mandatory descriptive and administrative metadata elements embedded, using e.g. Dublin Core (ISO 15836-1) and PREMIS formats. The use of a separate, METS based preservation layer enables the current long-term preservation applications to ingest EPUB publications. Producers and OAIS archives may also choose other approaches, such as embedding all metadata in EPUB publications or using another container standard. Whichever strategy is chosen, it should be planned out carefully. In the hybrid approach, some descriptive and administrative metadata needed during ingest may not be copied from the EPUB document to the METS document. In order to use this metadata, the OAIS archive shall have reading systems or other applications which are able to render EPUB publications and extract the relevant metadata from them. This document does not require copying of EPUB structural metadata to METS documents. Therefore, the structural metadata in METS is simple, only specifying the location of EPUB publication or publications in the SIP but not their internal structure. EPUB reading systems would not be able to use the structural metadata in a METS document, because they utilize structural metadata in the EPUB spine element when publications are rendered.
In order to eliminate uncertainty concerning the syntax and semantics of SIPs, submission agreements shall specify a METS profile or profiles which can be used to facilitate packaging of EPUB publications. This document can be used as a basis for these profiles. The profile can be part of the submission agreement, or linked to it. The latter approach was chosen in the Finnish Digital Library initiative; the benefit is that submission agreements will be relatively simple because technical details are stated in the document “Metadata requirements and preparing content for digital preservation” 7) . Finnish Digital Library initiative has published also a separate document titled “File formats” 8) , which lists the file formats suitable for ingest and preservation. Unfortunately, this document does not contain guidelines on how these file formats should be applied. EPUB is an example of a file format which is in principle archivable, but in practice can be used in a way which may makes long-term preservation challenging. The purpose of ISO/IEC TS 22424-1 is to provide guidelines for creation of archivable EPUB publications.