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URLibService User's Guide
Version 2.1


Chapter 4

Creating Persistent Citation Links

by Gerald J. F. Banon

Content

Preamble
Creating absolute links
Creating relative links within the URLib collection

Preamble

One of the most important issues in digital library is persistent citation linking. Frequently, a document contains citations to other documents. Links are used to access cited documents. A link is called persistent whenever it continues working after any document location changes.

In the first part of this chapter, we show how to create absolute links from anywhere to documents which are deposited in the URLib collection. These links might be or not be persistent.

In the second part of this chapter, we show how to create relative links between documents which are deposited in URLib collection. All these links are persistent.

You deposit a document in a URLib collection by downloading the URLibService Environment (see [1]), starting it (see Chapter 1), and pressing the Depositing a Document (DD) button. Alternatively, you can used an on-line submission form.

Creating absolute links

Up to now, links from outside the URLib collection must be absolute. Those from inside the URLib collection may be absolute.

Such links may be implemented in three ways.

In the first implementation, the HTTP URLs consist of three parts: a URLib Site Address, a Repository Name, and a File Name, separated by the words </col/> and </doc/>.

Here is an example of a link to the file <Readme.html> deposited in the repository <iconet.com.br/banon/2001/02.10.22.55> which is installed in the URLib site <mtc-m16.sid.inpe.br>:

<http://mtc-m16.sid.inpe.br/col/iconet.com.br/banon/2001/02.10.22.55/doc/Readme.html>

In the second implementation, the HTTP URLs consist of two parts: a specific URLib Site Address and a Repository Name, separated by </ibi-/> or </rep-/>.

Here is an example of a link to the document entitled What is URLib? deposited in the repository iconet.com.br/banon/2001/02.10.22.55:

<http://mtc-m16.sid.inpe.br/ibi-/iconet.com.br/banon/2001/02.10.22.55>

OBSERVATION: in these examples, the above two links point at the same file <Readme.html>. In the second implementation this file name may be omitted because it is the value of the Target File attribute in the metadata of the document. Nevertheless, if the file you want to access is not the file defined in the target file attribute, you can access it just by concatenating its name at the end of the previous HTTP URL, as shown below:

<http://mtc-m16.sid.inpe.br/ibi-/iconet.com.br/banon/2001/02.10.22.55/Readme.html>

In the third implementation, the HTTP URLs consist of two parts: the domain name of the permanent URLib site: <www.urlib.net>, or simply <urlib.net>, and a Repository Name, separated by </ibi-/> or </rep-/>.

Here is an example of a link for the document entitled What is URLib? deposited in the repository <iconet.com.br/banon/2001/02.10.22.55>:

<http://urlib.net/ibi-/iconet.com.br/banon/2001/02.10.22.55>

We recommend this last implementation over the previous ones for the following reasons.

i. As opposed to the first implementation, the second one is able to resolve the problem of locating the repository stored in another URLib site. Actually, the second implementation triggers a search procedure among a predefined set of URLib sites. However, one should observe that this sort of link is not totally persistent since it is based on a given URLib site address which might, one day in the future, fail to exist.

ii. As opposed to the first implementation, the second one is more robust in the sense that it is not sensitive to Target File name changes.

iii. As opposed to the first implementation, the second one automatically updates the Access Statistics of the specified repository.

iv. The third implementation has all the advantages of the second one, and compared to the second one, it has a higher degree of persistence since it depends on a permanent URLib site address.

OBSERVATION: in the current implementation, we can use simply </> instead of </ibi-/>. Here is an example of such simplification:

<http://urlib.net/iconet.com.br/banon/2001/02.10.22.55>

The link just above is an example of the simplest type of absolute persistent link. This is this type we recommend to use if the upper horizontal menu bar is not required (see next observation).

OBSERVATION: if, instead of </ibi-/> we just use </ibi/>, then a horizontal menu bar is displayed on the top of the Web page. Here is an example of such link:

<http://urlib.net/ibi/iconet.com.br/banon/2001/02.10.22.55>

Finally, whenever a document is available in several languages, it is possible to access it automatically in the preferred language just by concatenating the symbol <+> to the name of the repository containing the original version.

For example, the document in English (<en>) entitled What is URLib? is available in Portuguese (<pt-BR>) under the title O que a URLib?. The original version in English has been deposited in the repository <iconet.com.br/banon/2001/02.10.22.55>, its traduction in Portuguese has been deposited in the repository <iconet.com.br/banon/2001/05.25.16.44>. In order to access the document version according to the browser user preference, the HTTP URLs must be written as shown below:

<http://urlib.net/iconet.com.br/banon/2001/02.10.22.55+>

<http://urlib.net/ibi/iconet.com.br/banon/2001/02.10.22.55+>

This last HTTP URL displays the upper bar menu in the preferred language.

If the user language preference is Portuguese, then, in both cases, the document in the <iconet.com.br/banon/2001/05.25.16.44> repository will be returned.

Creating relative links within the URLib collection

URLibService allows the implementation of relative links between documents which belong to the URLib collection.

Persistent links consist of one of the words <goto-> or <ibi-> followed by a Repository Name, an IBIp or IBIn.

Here are examples of persistent links to access the document entitled What is URLib? deposited in the repository <iconet.com.br/banon/2001/02.10.22.55> and identify with the IBIp: <LK47B6W/E6H5HH>

<goto-/iconet.com.br/banon/2001/02.10.22.55>

<ibi-/iconet.com.br/banon/2001/02.10.22.55>

<ibi-/LK47B6W/E6H5HH>

Changing the text of the hyperlink, its new appearance can be:

<ibi-:LK47B6W/E6H5HH>

OBSERVATION: this HTTP URL is relative and can be resolved by URLibService since the current page has been deposited in a URLib Repository.

OBSERVATION: if, instead of the words <goto-> and <ibi->, we just use the words <goto> and <ibi>, then a horizontal menu bar is displayed on the top of the document. Here are examples of such links:

<goto/iconet.com.br/banon/2001/02.10.22.55>

<ibi/iconet.com.br/banon/2001/02.10.22.55>

<ibi/LK47B6W/E6H5HH>

Changing the text of the hyperlink, its new appearance can be:

<ibi:LK47B6W/E6H5HH>

Finally, as in the previous section, whenever a document is available in several languages, it is possible to access it automatically in the preferred language just by concatenating the symbol <+> to the name of the repository containing the original version.

For example, to access the document entitled What is URLib? available in English and Portuguese according to the browser user preference, the HTTP URLs must be written as shown below:

<goto/iconet.com.br/banon/2001/02.10.22.55+>

<ibi/iconet.com.br/banon/2001/02.10.22.55+>

<ibi/LK47B6W/E6H5HH+>

Changing the text of the hyperlink, its new appearance can be:

<ibi:LK47B6W/E6H5HH+>

Sometimes it is the metadata which are in several language. For example, the content of the repository <dpi.inpe.br/banon/1998/08.02.08.56> (URLibService) is described by a set of metadata in English and another one in Portuguese. In this case, the browser user preference defined the upper horizontal bar menu language:

<ibi/dpi.inpe.br/banon/1998/08.02.08.56>

Nevertheless, it is possible to force the upper horizontal bar menu be in English:

<ibi/dpi.inpe.br/banon/1998/08.02.08.56?languagebutton=en>

or in Portuguese:

<ibi/dpi.inpe.br/banon/1998/08.02.08.56?languagebutton=pt-BR>

OBSERVATION: The above rules applies to metadata as well. Nevertheless, since there doesn't exist metadata for metadata, just the the words <ibi-> and <goto-> are valid.

Here is an example of a relative link for the metadata of the document entitled What is URLib?, deposited in the repository <iconet.com.br/banon/2001/02.10.22.55.05>

<ibi-/iconet.com.br/banon/2001/02.10.22.55.05>

Relative links have the higest degree of persistence of all the previous types of link since even the type of communication protocolo (HTTP) and the site Address are now hidden.