The aim of this page is not to fully explain KDE's Semantic Search technology and every detail, but to give a short overview, some examples, share the vision behind it and link to relevant information on the web.
From KDE Applications 4.13 onwards, the 'Baloo' file indexing and file search framework replaces Nepomuk. Read details on the changes for Applications 4.13 here. Semantic Search no longer uses a single, big database, but separate, specialized databases for each type of data. The new search databases are in $HOME/.local/share/baloo. If you upgraded to KDE Applications 4.13 from an earlier KDE release, you can delete $KDEHOME/share/apps/nepomuk.
As the Glossary mentions, Semantic Search is about classification, organisation and presentation of data. It is not an application, but a component which can be used by developers within applications.
For example, the Dolphin file manager makes use of Search. In KDE Applications versions prior to 4.13 Semantic Search must be enabled from . The information sidebar of Dolphin ( , or press F11) presents information extracted by Search about the selected file, and also allows you to assign tags, ratings and comments to files. This information is then stored and indexed by Search. You can then search for metadata using the navigation bar in Dolphin. Click to , or press Ctrl+F, and search for file names or file contents.
KDE's Semantic Search offers several 'layers' of functionality to applications. The first and most simple of those is manual tagging, rating and commenting, as used in Dolphin. This helps you to find your files faster, but is also a lot of work.
To make finding files containing text easier, Search offers a second functionality: indexing the text of files. You can find files by entering some words which you know are in there, or just (part of) their title.
The third layer is a very complex one, and the reason why the underlying technology, Nepomuk, was conceived as a research project of several companies and universities in the European union. This is where you will find difficult words like 'semantic desktop' and 'ontologies'. Basically, it is about context and relationships.
Search does not index every file on the hard drive. Its default configuration in most Linux distributions excludes some common patterns for backup files and configuration directories. You can change this in. Add folders to be excluded. If you want to turn off indexing of files entirely, just add your home folder there.
In System Settings you can also control whether Search indexes files on removable media such as USB drives and CD-ROMs. In KDE Applications 4.13 this is not available, removable media are not indexed. Future versions are planned to reintroduce this functionality.
Let me try to explain what Semantic Search offers using two examples. These features are not available fully yet - the base is there but application developers need to integrate this in their applications.
Now Semantic Search aims to help you. You know this file came from that friend of yours, your computer does not know. Search, however, can remember this relationship. Searching on the name of your friend will therefore pop up the photo!
Another potential relationship is between a web page you copied text from and the document you pasted it into, or two images showing the same car. Such relations can sometimes be extracted from the files themselves (you could analyze photos and see who or what is on there) or supplied by the applications involved (as in the above email example). This part of Search is still under heavy development, and needs integration in applications, so you can expect it to take a few more years to really shine.
All in all, this part of Semantic Search is about making search smart. Think about how Google tries to be smart with your searches: when you search for a hotel and a city name, it shows above the website results a google map showing hotels in the city you mentioned! It might even suggest a better name in case you made a spelling mistake. Google also tries to put the most relevant information on top of the list of results, using complex calculations on relationships (links) between websites. Semantic Search will be able to offer such smart results and order them on relevancy using relationship information.
These relationships can not only help you while searching for files, but also have an influence on applications and what information they present. Note that this way of using Search is still more a vision than reality! Many of the components are in place, but it is not yet integrated in applications and the desktop as a whole.
Enter 'activities'. These have been introduced in Plasma, and currently offer different 'desktops'. They are a bit like virtual desktops, except that the desktop itself changes, not the set of applications. Different widgets, background, things like that. Of course, since Plasma 4.3, each virtual desktop can have its own activity, bringing the two in sync.
如果程序和桌面认识活动，你可以根据经常工作的任务创建活动。所以如果你经常不得不修改带报价的电子表格，你创建这样一个活动：摆放一个「文件夹视图」（或多个）部件到桌面上，添加一个计算器和一个 todo 部件来记录还需要修改的东西。可能需要一个「邮件文件夹」部件来显示有关报价表问题的邮件！
The scenario described above is already partially implemented in the Activities but much work is still left.
The following is taken from a KDE forums post. Please feel free to add/remove/modify details if you have the time!
In versions of the KDE Applications before 4.13, Semantic Search would have components running separate from applications. This functionality could be disabled by unchecking Desktop Search section of System Settings. In case you want to turn off all semantic features, uncheck . Notice that this will turn off search in Dolphin as well.in the
Virtuoso is no longer used by Semantic Search starting the Applications 4.13 release.
在给出其它链接前我要指出的是：共享 Nepomuk 数据。如果你的标记（tags），评分（ratings）和注释（comments）能够在你发送文件给其他人时同时共享给他会很棒。但是,要是你给一个联系人打上了“麻烦”的标签('在床上烦人')，然后发送这个联系人的信息给一个共同的好友，但你又不希望这个标签也一并发送过去...
这个问题当然在考虑之中，是 Nepomuk 研究的一个重要课题。由于这些隐私顾虑，外加技术挑战，所以暂时 Nepomuk 内容是私有的。放心，Nepomuk 团队尽其可能尊重你的隐私。
The new Search technology (post KDE Applications 4.13):
The old Search technology: