About the DFG Viewer
The DFG Viewer is the reference implementation for the following data format standards: METS/MODS and METS/TEI as well as the exchange interface OAI-PMH used by architects, art historians, etc. Since these are also common international standards, the DFG Viewer can be used by projects that have not received funding from the DFG. The only requirements are compliance with the aforementioned standards and unrestricted accessibility of the digitized material on the Internet. Furthermore, a user does not have to install or operate the software themselves. The service is free of charge for both the data provider and the users and follows the "Digitization" rules of practice set out by the Deutsche Forschungsgemeinschaft (DFG) (DFG, German Research Foundation) for all funded projects.
How does it work?
The implementation of the DFG Viewer is very simple: when the DFG Viewer is called up, a link to the technical encoding of the digitized material (in METS format) is passed as a URL parameter. The web service retrieves the referenced METS file from the provider and extracts all the necessary information for displaying the digitized item and other additional functions. Since the links to the METS files are usually unchangeable, the resulting DFG Viewer calls can be easily stored on websites or in reference systems such as library catalogs to allow users to view a digitized item with a single click.
The DFG Viewer offers a dynamic range of functions depending on the available data quality of the METS file and the document type. At a very least, the user can browse through the digitized material, continuously zoom in and out, and switch between a single-page and double-page view (optionally in full-screen mode). In addition, the user receives a basic set of metadata describing the digitized material (usually title, author, place and date of publication), as well as information about the provider of the digitized material. If additional information is available in the METS file, the following functions are automatically offered in addition:
Table of Contents
If the METS file contains structured data, in other words an outline of the content of the digitized material, the DFG Viewer displays this as a table of contents and allows the user to navigate through the digitized material. If the pagination is also recorded, the DFG Viewer displays the corresponding page numbers in both the table of contents and the page selection (in the case of manuscripts, also the page count according to the foiling).
If further descriptive metadata (such as article titles and authors) has been recorded in addition to the bibliographic title data, this information is also displayed as soon as the user opens the corresponding structural elements. The display takes place in a drop-down box, so that it is up to the user to decide how much space he or she wants to dedicate to the metadata.
Depending on the media type, the metadata can be encoded in both MODS and TEI formats. While the former is predominantly used for printed works, the latter is common for medieval and early modern manuscripts.
Permalinks and Download
If the data provider provides permalinks for scientific citation for the digitized work and these are specified in the METS file, the DFG Viewer also displays these references and thus allows the user to address the digitized work and page in a scientific context.
Optionally, the data provider can also allow a PDF download of the digitized work (as a whole work or individual pages). In this case, the DFG Viewer displays corresponding buttons that can be used to trigger the download.
Newspapers in particular, but also other periodicals with a long publication history, are traditionally indexed chronologically and presented in a calendar view. The DFG Viewer automatically recognizes such digitized material on the basis of its chronological structure, which is distributed over three separate METS files. The DFG Viewer then offers a three-level navigation via the selection of a year, followed by an overview of the publication history within this year up to the display of a specific issue. Of course, the reverse navigation from the issue to the volume or to the overview of the entire title is also possible at any time. Within an issue, all other functions of the DFG Viewer are available to the user as usual, including a possible further subdivision of the content of the issue by means of a table of contents.
The DFG viewer can also display full texts, if they are available in ALTO format with word coordinates for the digitized material. The DFG Viewer uses the word coordinates and the zoom level selected by the user to determine the exact position of the words on the scan. If the user now selects a section of the image, the text located there is displayed in a separate view and can be easily copied as a quotation. Even text passages that are difficult to recognize or unfamiliar Fraktur fonts can be read smoothly in this way.
If the data provider also has a full-text index with a public SRU interface, the DFG Viewer offers the user a search slot for full-text searches. This allows the user to search either within the current digitized material or even in the provider's larger holdings. The results are in turn displayed directly in the DFG Viewer, so that the user does not have to switch between several systems and providers for this purpose.
The development of the DFG Viewer was and is funded by the DFG, while the SLUB Dresden ensures the permanent operation in a powerful server in its own responsibility. The source code of the DFG Viewer is free and can be obtained under the open source license GPL3 on GitHub and reused free of charge. The platform also allows users to contribute their own further developments to the project.