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Introduction

One very important aspect of making digital objects available online is the ability to creat permanent links create permalinks to those objects. Such links may be useful, for example, in a scientific work, as an element of a bibliography, or for referring to digital objects in external services, such as library catalogs, bibliographic bases, or even Wikipedia. This section is about the way in which links to digital objects are created in the dLibra system; it is also explained which of them should be used to ensure the maximum durability of the references.

The Data Model of the dLibra System

In the image below, the basic data model in the dLibra system is shown. The model includes:

...

The Types of Links and the Manner of Processing Reader Queries

In table 1, two types of links to particular elements of the data model in the dLibra system are shown. That differentiation results from the assumed manner of processing reader queries, illustrated in figure 2. The key differentiation here is the one between the reader application and the permalink module. The task of the module is to make a part of the links in the dLibra system independent from the technological changes in the reader application which are related to developing it, making its subsequent versions available, and technological modernizations. Examples of such permalinks are shown in the last column of table 1. The task of the module which manages those links is ensuring their unchanged functioning despite the changes introduced in the subsequent versions of the reader application. The penultimate column in table 1 contains links which have been unchanged in the dLibra system since its 0.4 version, published in 2004. Those links, however, may – in theory – be changed in the future, for technical reasons. That is why it is recommended that the permalinks presented in the last column be used for creating references to objects.

...

Fig. 2. A simplified schema of the architecture of the dLibra system.


Permalinks and Exceptional Situations

In some specific cases, permalinks cannot be offered solely on the basis of the digital library system. When we look at a sample permalink (for example, http://www.wbc.poznan.pl/publication/290787), we can say that it has two elements which can change. They are:

...

Summary

By way of a summary, the table below contains the advantages and disadvantages of particular kinds of links to objects available in the dLibra system.

Object typeThe link used inThe effect of calling the objectCommentRecommended?

Group publication

http://www.wbc.poznan.pl/publication/4081Displaying the structure of a group publication
  • A reference through a permalink link which is independent of the version of the Reader Application.
(plus)
http://www.wbc.poznan.pl/dlibra/publication/4081Displaying the structure of a group publication
  • A reference directly to the Reader Application; in theory, the URL structure may be changed in the future.
(error)
Publicationhttp://www.wbc.poznan.pl/dlibra/publication/291316

Displaying the metadata of the only available release edition of the given publication or a list of links to the releases editions of that publication when there is more than one release edition of that publication (in practice, that is a very rare occurrence).

  • A reference directly to the Reader Application; in theory, the URL structure may be changed in the future.
(error)
http://www.wbc.poznan.pl/publication/291316Displaying the metadata of the only available release edition of the given publication or a list of links to the releases editions of that publication when there is more than one release edition of that publication (in practice, that is a very rare occurrence).
  • A reference through a permalink link which is independent of the version of the Reader Application.
(plus)
http://www.wbc.poznan.pl/dlibra/publication/291316/edition/239649/content

Displaying the content of the only available release edition of the given publication or a list of links to the releases editions of that publication when there is more than one release edition of that publication (in practice, that is a very rare occurrence).

  • A reference through a permalink link which is independent of the version of the Reader Application.
  • It causes the display of content in the interface of the digital library, which gives the reader access to the metadata of the presented object, the list of related objects, etc.
(plus)
ReleaseEdition http://www.wbc.poznan.pl/dlibra/publication/291316/edition/239649 Displaying the metadata of the given publication releaseedition.
  • A reference directly to the Reader Application; in theory, the URL structure may be changed in the future.
  • A reference to a particular release edition of the publication, which can cease to be available to readers after another release another edition of the same publication has been created and made available.
(error)
Filehttp://www.wbc.poznan.pl/Content/239649/Displaying the main file of the given publication releasepublication edition
  • A reference to a particular release edition of the publication, which can cease to be available to readers after another release another edition of the same publication has been created and made available.
  • A reference directly to the content; it causes the display of the file without the interface of the digital library, which prevents the reader from seeing the object metadata.
(error)
http://www.wbc.poznan.pl/Content/239649/7_Studies_2012_3_135.pdfDisplaying a particular PDF file of the given publication releasepublication edition
  • A reference to a particular release edition of the publication, which can cease to be available to readers after another release another edition of the same publication has been created and made available.
  • A reference directly to the content; it causes the display of the file without the interface of the digital library, which prevents the reader from seeing the object metadata.
  • A reference directly to the name of the file, which can be changed when the files comprising the given digital object object are changed (regardless of a change of the release edition identifier), for example, because the original digital format of the file becomes obsolete.
(error)
http://www.wbc.poznan.pl/Content/239649/7_Studies_2012_3_135.pdf#page=3

Displaying a particular fragment (page 3) of a particular PDF file of the given release edition of the publication.

  • A reference to a particular release edition of the publication, which can cease to be available to readers after another release another edition of the same publication has been created and made available.
  • A reference directly to the content; it causes the display of the file without the interface of the digital library, which prevents the reader from seeing the object metadata..
  • A reference directly to the name of the file, which can be changed when the files comprising the given digital object object are changed (regardless of a change of the release edition identifier), for example, because the original digital format of the file becomes obsolete.
  • A reference to a particular fragment of a file (page 3) is made through an additional parameter, which does not have to be supported by the file browser used by the reader.
(error)

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