A null-edit ("zero-diff-save") is a walk-around for a problem that occures with Semantic Mediawiki.
How to do a null edit
Click the edit button of the page that call recently implemented semantic material (e.g. the overview page) and then click the save page button without changing anything. Then the semantic database is updated and the new data will occure in the corresponding page. For now, this is the only way to keep the system up-to-date. Another solution for this problem is in progress.
Semantic MediaWiki is an extension to MediaWiki, the software this wiki is written in. It provides several functions that allows you to annotate articles in this wiki. This means you can give properties and its value to an article. These property-value-article-triplets are stored in a database table, like the whole wiki is stored in such tables.
The second feature of Semantic MediaWiki is the possibility to create querries. In these querries you can make accessable certain properties, their values and the articles that have these properties with custom restrictions. Some articles in this wiki have included such querries. If you save such a page, the corresponding item in the article database is updated. The results of these querries are a part of the article. Every time you save an article that has a querry in it, the result of this querry is updated: The page-save script looks into the databases for attributes, values and articles and adds the relevant information to the querry-article.
If you save a page that contains semantic data both article and semantic tables in the database are updated. The problem is, that the article with the querry in it doesn't know that you have changed the information on your properties, it's values and the articles that have these properties. You have tell the querry that the datas have been changed. The easiest way to tell this to the querry is to do a zero-diff-save. There are other ways to update the semantic articles, but these take a lot of time and bandwidth. Such maintainance scripts look through all articles, attributes and values. The larger the wiki is the (exponentially) longer takes such a semantic database update. Also, this updates can only be performed by an admin. If you want to see the results of a semantic querry in order to check the newly added semantic data, e.g. in a AllMorphemes-page, immediately, you must perform a zero-diff-change.