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Help & guidance Guides to Good Practice

Preservation formats

Harrison Eiteljorg II, Kate Fernie, Jeremy Huggett and Damian Robinson, with additional contribution by Bernard Thomason. Revised by Stephen Dobson, Ruggero Lancia and Kieron Niven (2011), Archaeology Data Service / Digital Antiquity, Guides to Good Practice

Deposit formats

As discussed in the opening sections of this guide, while other fields have seen many data formats appear over the last few years that are intended to make data exchange and migration easier, little has changed in the field of CAD. The most popular formats, although widely used, remain proprietary (i.e. they are marketed by a single company) and few open standards that are independent of the software used exist (see the general section on Planning for the creation of digital data). Recent developments by the Open Design Alliance have however created tools which now allow other software packages to provide greater support to read and write DXF and DWG files via Teigha[1].

Most digital archives have documented guidelines for depositors but others set terms and conditions for each project and each new deposit. When selecting and depositing data, the best approach is always to contact the repository early in the project. It is possible that an archive might decline the data offered, where they are considered to be of limited relevance to the users of a particular repository or uniquely difficult to migrate. Different archives are also pursuing different approaches to underwriting the costs of archival storage and costs should be discussed at the outset.

While the format in which you deposit data will depend to some extent on the type of information contained within, the formats outlined in the table below are those generally recommended for deposit, long-term preservation and for online dissemination. Delivery formats pertain to the file types that will be accepted by an archive as a component of a deposit. Where necessary these delivery file formats will be migrated into a preservation format for long-term storage and may also be converted to a dissemination format for online delivery to users. Dissemination formats may also include widely used proprietary formats as well as formats which simplify or compress data which may have no long-term preservation potential. For CAD data, files in DXF and DWG formats are recommended for deposit and long-term preservation. Files may also be translated to DWF or PDF for online dissemination.

Preservation and dissemination formats

Format Requirements
DXF The preferred format for preserving and disseminating CAD data. Preference should be given to the ASCII version of the format.
DWG The DWG format provides an alternative to the DXF format where file size or full compatibility may be an issue.
PDF PDF files (particularly PDF3D) present a quick and relatively self-contained alternative to native CAD files for viewing CAD models. However, it should be noted that once in a PDF file, CAD data xcannot be imported and reused in a CAD application.

For other data types associated with CAD files, please see the relevant guide: