Emulation and Rendering Tools (CPP-015)

Definition and scope

Digital preservation is all about ensuring long-term access to digital content despite the challenges of obsolescence, degradation, and technological change. Emulation and Rendering tools are important strategies in achieving that goal, and together with File migration ensure that digital content remains usable to the Designated Community.

Emulation attempts to recreate the original habitat - both hardware and software - of the digital Object in order to interact with it in the way it was intended. This is achieved by preserving both the content and the experience of the original environment. The purpose of emulation is to simulate the original operating system and the tools that are needed to interact with the Object.

Rendering tools interpret and display the digital Objects in the current environment using viewers based on modern technology. It is not uncommon for rendering tools to convert the digital Object into a more accessible form before displaying it. In such cases, viewers and converters collaborate to achieve the required result.

In addition to maintaining the Bitstream integrity of its holdings, semantic digital preservation entails ensuring their continued readability and usability. This necessitates that the TDA identifies the required environments and tools to support the actions its Designated Community is authorised to perform, regardless of whether direct access to the holdings is currently being provided.

Emulation and Rendering are two very different techniques to achieve a similar goal. They differ in some essential aspects:

• Authenticity: Emulation aims for the best authenticity by reproducing the entire look and feel of the original environment. The output of the rendering process may do a pretty decent job in reproducing the original Representation of the Object, but the interaction will be simulated at best. The rendering’s conversion operation can be lossy and generate a less accurate result. Rendering is also more vulnerable to slight format changes and thus requires Format Validation.
• User Experience: Again, Emulation obtains the highest score as it will reinstate the original hard- and software as good as possible and allows the user to interact with the Object to its full potential. Rendering will typically reduce the experience to a read-only view of the data with a limited set of operations available.
• Preservation Scope: In order to render the Object, only the content needs to be preserved. For emulation, however, both content and its environment need to be preserved.
• Technical Overhead: The requirements for Emulation are very high. A lot of resources (e.g. CPU and memory) are required to fire up the emulation. Moreover, the configuration and maintenance of an emulation environment is complex and time consuming. Performance may suffer and emulation does not scale easily. Rendering on the other hand, is relatively simple to set up, especially when no conversion is required or the conversion is done beforehand. Performance is mostly great, unless the Object is stored in slow off-line storage. The technique causes little problems for scaling.
• Licensing: Licensing of the operating system and software interacting with the Object may be a concern for emulation. For rendering of most common file formats, open source libraries and tools are available and licensing is less of a concern.

The choice for emulation versus rendering is captured in the Emulation and Rendering Policy. There are many possible decision factors and strategies for choosing emulation over rendering. For example:

• Manual configuration by archive maintainer;
• Requested by consumer;
• Decision based on format;
• Decision based on Technical metadata;
• Decision based on collection preferences, policies, agreements with producer, etc.