Digital Libraries
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Digital Libraries |
PAGE (5 of 5) |
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Digital library has had many successful research results that most of us are blissfully benefiting from albeit unknowingly. Most of the results are of a technical nature that is beyond this course. However, we will discuss a few of the minor results that everyone might consider employing.
PURLs, persistent URLs, were developed to solve the problem of finding Web pages that have moved since one has last visited them. With the ultra-dynamic nature of the Web this is truly a common pervasive problem. (Domain name server machines, which maintain common Web databases of machine addresses, solves a related problem by allowing users to find servers on the Net after they have relocated.)
A PURL link is directed to a PURL server machine that maintains a database of of document names and current document URLs. When one clicks on a PURL link the PURL server finds the actual document URL and seamlessly transfers the user's browser to it. PURLs behave almost the same as regular URLs in Web documents and even looks the same:
http://machine.subdomain.domain/directory/subdirectory/document
However the usual Web suffix, .html, is usually omitted. PURLs reqire that Web authors register with PURL servers and update their document URLs whenever they change. OCLC maintains a PURL server that allows for free registration for Web authors.
Watermarks in traditional print are often used to identify the manufacturer of the paper. They can be viewed usually by holding the pages up to a strong light. Research is ongoing to discover uses for watermarks as a means of copyright protection for digital works. There are two categories of watermarks. Visible watermarks are transparent/translucent images that are overlaid on existing images. Examples can be seen often on television as opaque embossed network logos in the corner of the screen of a broadcast event. Geocities, a free Web page provider, recently started using automatic watermarks on user pages. Invisible watermarks are hidden watermarks that can only be detected by software analysis of the stored image. Free and commercial software for watermark creation/embedding and detection is available.
Metadata is information that is stored about other data and is used to perform tasks upon the original data. A card catalog in a library is an example of metadata. It is used to identify, describe, and locate the actual data that the catalog stores information about. Metadata can be considered any data that is stored about other data. In databases metadata is considered to be the data dictionaries, relational schemas and underlying storage representations. In a HTML Web document the metadata might be considered to be the hyperlinks and the <META . . . > tag attributes, etc.. For example, the META tags for this document are:
<META name="Digital Library" content="CS Dept VA TECH">
<META name="keywords" content="library">
Software tools already exist for creating/generating metadata about documents: Reggie, PrismEd, AGLS Metadata Editor, Xtme, MMM (Mathematics Metadata Markup editor, Trellix, etc.
PURLs
Watermarks
Metadata
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© CS Dept Va Tech, 1998. |
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