Цифрлік объектілерді сақтау үшін UVC негізіндегі стратегия

UVC based preservation is an archival strategy for handling the preservation of digital objects. It employs the use of a Universal Virtual Computer (UVC)—a virtual machine (VM) specifically designed for archival purposes, that allows both emulation and migration to a language neutral format like XML. The dominant approach to digital preservation is migration. Migration entails making periodic transformations of archived information into new logical formats as their native formats, or the software or hardware on which they depend becomes obsolete. The notable danger of migration is data loss, and possible loss of original functionality or the ‘look and feel’ of the original format. Furthermore, digital migrations are time consuming and costly as the process requires converting the format of every document, in addition to copying converted bit streams to new media as necessary.

Jeff Rothenberg caused a bit of stir in organizations concerned and responsible for digital preservation with his report in 1999: "Avoiding technological quicksand: Finding a viable technical foundation for digital preservation". He states that there are no viable solutions to ensure that digital information will be readable in the future. The proposed solutions of relying on standards and migrations are labeled time consuming and ultimately incapable of preserving digital documents in their original form. He suggests:

"an ideal approach should provide a single, extensible, long term solution that can be designed once and for all and applied uniformly, automatically, and in synchrony (for example, at every future refresh cycle) to all types of documents and all media, with minimal human intervention." He proposes that the best way to satisfy the above criteria is Emulation by; developing an emulator that will run on unknown future computers; developing techniques to capture the metadata needed to find, access and recreate the document; developing techniques for encapsulating documents, their attendant metadata, software, and emulator specifications. In 2000, he suggests implementing an emulation based preservation approach in which emulator specification are expressed as programs and interpreted by an emulator specification interpreter program written for an emulation virtual machine. Rothenberg's approach was met with skepticism and considered too technically challenging, too expensive and too time consuming, and therefore an economic risk (without the support of empirical evidence). (See further reading section)

Raymond A. Lorie, during his employment at IBM Research Centre Almaden, initiated the development of a UVC based solution to long term digital preservation. He describes the approach as ‘Universal’ because its definition is so basic that it will endure forever, ‘Virtual’ because it will never have to be physically built and it is a ‘Computer’ in its functionality. IBM (NL), the asset owner of the UVC, continues to develop the UVC concept within the PLANETS project. Raymond van Diessen is responsible for extending the application of the UVC concept to preserve more complex objects.

The National Library of the Netherlands (Koninklijke Bibliotheek, KB) played a major role in demonstrating that emulation based on the UVC concept is a viable option for long term digital preservation. In 2000, the emulation advocate, Jeff Rothenberg participated in a study with the KB to test and evaluate the feasibility of using emulation as a long term preserving strategy. His method was to use software emulation to reproduce the behaviour of obsolete computing platforms on newer platforms offering a way of running a digital document’s original software in the far future, thereby recreating the content, behaviour, and ‘look and feel’ of the original document. Rothenberg was criticized for trying to preserve the wrong thing by suggesting to emulate the behavior of old hardware platforms and operating systems to access the original data through the original software program associated with it. Raymond A. Lorie recognized the difficulties in trying to create a program to emulate a 'real' machine on a future platform and realised that this approach was overkill for the purpose of preserving digital objects. Instead he introduced a novel approach of data/program archiving using a ‘Universal Virtual Computer’. Creating a UVC for PDF documents is more complex. Instead the KB decided on developing a UVC for images because this approach would also cover PDF documents (a PDF file can easily be converted to a series of images). The UVC based approach resulted in the UVC as one of the permanent access tools for JPEG/GIF87 images within the Preservation Subsystem of the KB’s e Depot. Following the successful implementation of the UVC, the KB has continued to develop their emulation strategy for long term digital preservation by focusing on 'full' or hardware emulation. This approach delivered a durable x86 component based computer emulator: Dioscuri, the first modular emulator for digital preservation.

The Universal Virtual Computer is part of a broader concept, called the UVC based preservation method. This method allows digital objects (like text documents, spreadsheets, images, sound waves, etc.) to be reconstructed in its original appearance anytime in the future. The methods are programs written in the machine language of a Universal Virtual Computer (UVC). The UVC is completely independent of the architecture of the computer on which it runs. The UVC itself is a program which contains a set of instructions rather than a physical computer. It will run as a software application on a future platform. Because we do not know at this time which hardware is available in the future, the UVC must be created at the time we want to access a particular document from the repository. This UVC then forms the platform on which programs can run that have been specifically written for such UVC in the past. Creating an emulation program for the UVC in the future is much simpler than trying to emulate a 'real' machine.

The method of a UVC based preservation strategy differentiates between data archiving which does not require full emulation, and program archiving which does. For archiving data, the UVC is used to archive methods which interpret the stored data stream.

Together with the original data it is possible to reconstruct the meaning of each particular digital object. The UVC can be seen as the heart of the system. Like the Java Virtual Machine and the Common Language Runtime, the UVC is actually an emulator which allows a program to run on virtual instances of the necessary, usually obsolete, hardware, and will continue to emulate the necessary hardware as technology continues to evolve. Because we do not know at this time which hardware is available in the future, the UVC must be created at the time we want to access a particular document from the repository. The UVC forms the platform on which programs specifically written for the UVC can run.

Different steps must be taken at archiving time (present) and retrieval time (future).

Step 1 Create an emulator on the current platform. Because of the simplicity of the UVC concept, it is fairly easy for skilled software developers to construct a UVC emulator for a particular platform of the time

Step 2 Develop a Logical Data Viewer (a restore program to restore the data). This is an application program that reads the UVC object code and the bit stream and invokes the emulator to execute the UVC program i. e. the program controls the UVC and all input/output interaction between it

Step 3 Write a restore program to restore the schema. Since the logical view for the schema information is fixed a single restore program may actually support all applications. If the future client already knows the logical view for the documents being restored then the schema does not necessarily needs retrieving. Furthermore, the schema only needs to be requested once for a collection of documents of the same type

The UVC program decodes the file format of a digital object. This format decoder program runs on the UVC, which is the platform independent layer, independent of future hard and software changes. Executing the format decoder delivers the element tags. These elements build the Logical Data View (LDV) of the data, which is quite similar to XML. The LDV is an instantiation of the LDS, describing the structure and meaning of the tags as parts of a specific information type. All these components are controlled by a Logical Data Viewer simply called viewer. For reconstruction, the viewer starts the UVC and feeds it with the data of the digital object to a format decoder running on top of the UVC. In return it retrieves an LDV and reconstructs a specific representation of the original object’s meaning.

The architecture relies on concepts that have existed since the beginning of the computer era: memory, registers and basic instructions without secondary features often introduced to improve the execution performance. The performance is of secondary concern as the UVC programs are run mostly to restore the data and not work with them. Speed is not a real concern either as future machines will be much faster, and an emulation of the UVC on a future machine will consequently run much faster. Furthermore, the flexibility of the UVC is more important than the speed of execution. Even so, performance can always still be improved.

The UVC for data archiving i. e. the archiving of static files, is proven to work in an operational digital archiving environment. The UVC is one of the permanent access tools for images at the KB.

The UVC is proven to successfully restore digital objects in their original form. The application is simple because with images no functionality is needed. The approach to develop a UVC for JPEG images is justified as most formats can be converted to this format. For example, a PDF document can be displayed as a series of JPEG images thereby retaining the 'look and feel' of the original digital object but sacrificing the functionality. Furthermore, the application for JPEG images can be easily adopted to emulate TIFF images by making a small adjustment to the Logical Data Schema. The approach can also be applied to all other objects which do not contain behavioral aspects. For example, interpreters have been written (partially) for Excel, Lotus 1 2 3 and PDF. However, these applications only handle the static features of the formats.

UVC based emulation uses the UVC as a universal platform on which a platform independent emulator can be built. The UVC (software program) recreates a simple general purpose computer and can be easily implemented on any computer platform now and in the future. With this strategy future users should always be able to access and view the original object. The official UVC specification must be preserved at preservation time. Also decoders must be developed for each specific file format and a LSD is required for each type of digital object, defining object types by image, sound, spreadsheet, text, etc. And of course the original objects should be preserved as well.

As mentioned before, the UVC based approach has only been effectively implemented for static files. The technology continues to be developed by Raymond van Diessen (IBM) to include dynamic objects by exploiting the communication facility between the UVC program and a future application.

Copyright issues for this approach are not expected to be different from those of any other approach. If intellectual property rights exist for a format this issue has to be taken up with the format owners. Similarly, to 'UVC enable" applications the source code is required from the developer and therefore permission from the owner. Lastly, for hardware emulation, all the relevant licenses of the software running on the system are required.