A publication is a unit of information such as an article, report or user's manual. dLibra publications consist of files. In the simplest case a publication can contain only one file that conveys all the information (e.g. a PDF, PS or MS Word document). Nevertheless, it is also possible that a single publication will comprise many files of different types. The prime example of such a publication is a web page with HTML, JPEG, GIF and other files as its components.
While developing an electronic document it very often is necessary to update or modify its content. As the previous versions of the publication may have already been published (made visible to the readers and library users) it is not possible to withdraw them from the library. Instead, new versions of the changed publication files can be stored in the library so that both the previous versions and the new ones are accessible. Creating a new version of a file does not, however, mean creating a new publication. The relationship between versioned publication files and the publication itself is covered in the next section.
A publication can be made visible to the library users by creating an edition. An edition defines which versions of publication files will compose the document to be presented to the user. Obviously, a single publication can have many editions including different versions of publication files or even different files.
To further investigate the idea of file versioning let us assume there is a publication consisting of only three files: body.html, title.jpg and logo.gif. The figure Figure 1.1, “File versioning and publication editions” shows how can subsequent versions of these files make publication editions.
In the figure, the sample publication starts from only one file: body.html. The first edition of the publication contains only this file, whereas the other files may or may not exist as well. Each publication object is versioned, which enables the editors to store subsequent revisions of the object and to place them in different publication editions. The second edition of the sample publication, apart from a revised body.html file, contains a new file: title.jpg in its initial version. The third edition comprises all the three files.