Editing EPrints Glossary (section)

== V ==
=== View page ===
The view page displays information about a [[#Data object|data object]], typically an [[#EPrint|eprint]].  This is why "view page" is often used as shorthand for [[#EPrint view page|eprint view page]].

=== Virtual dataset ===
A virtual [[#Dataset|dataset]] is one that is derived from a real dataset.  In particular, [[#EPrints repository software|EPrints repository software]] has virtual datasets for:
* [[#Live archive|Live archive]] 
* [[#Review buffer|Review buffer]] 
* [[#User workarea|User workarea]] 
* [[#Retired|Retired]] 
All of these are sub-sets of the [[#EPrint|eprint]] dataset where the [[#EPrint status|eprint status]] is a particular value.  

Additional virtual datasets can be configured for a [[#Repository|repository]] or at an [[#Archive level|archive level]]. 

=== Virtual metadata field ===
This is a [[#Metadata field|metadata field]] whose values are not actually stored in the database but are generated dynamically by a function probably using the values of one or more other metadata fields.  This may be useful when editing the [[#Citation|citation]] style as part of designing your [[#Archive|archive]]'s [[#Abstract page|abstract page]], as being able to reference a field is very straightforward.  A basic example might be that you want to display on the abstract page the number of [[#Document|documents]] for the [[#EPrint|eprint]].  Creating a virtual field for the eprint called ''num_docs'' might look as follows:
 {
   name => 'num_docs',
   type => 'int',
   virtual => 1,
   render_value => 'get_num_docs',
 },
Then you would define a function in a configuration file and assign it to <tt>$c->{get_num_docs}</tt>.  You could then simply include this in the ''summary_page.xml'' eprint citation file as:
 <epc:print expr="num_docs"/>

=== Visitor ===
A visitor to an [[#Archive|archive]] is distinguished from a [[#User|user]], as they are not logged in and they are accessing the archive anonymously.  They are probably just wanting to view an [[#Abstract page|abstract page]] or download an open access publication [[#Document|document]].

=== Volatile metadata field ===
This is a [[#Metadata field|metadata field]] that is liable to change on a regular basis but does not really affect the overall content of the [[#Data object|data object]]'s [[#Metadata|metadata]], so should not prompt a new [[#Revision|revision]] to be generated.  A metadata field can be made volatile by setting the following attribute in the field definition:
 volatile => 1,
Metadata fields that are only intended for administrative purposes are often defined as volatile, such as the [[#EPrint|eprint]] [[#EPrint locking|edit_lock]] metadata field.  If a [[#User|user]] takes an edit lock on an eprint, if the edit_lock metadata field was non-volatile, this would lead to a new revision being create for the eprint when ultimately nothing had yet changed.  In fact, worse still, if the edit lock was released without making any changes, a further revision would be created, which would be basically the same as the revision before the user took the edit lock.