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Nepomuk

這個頁面的目的不是詳細解釋Nepomuk技術及其每個細節，而是作簡短的概述，舉一些例子，分享其背後的設想和給予指向網上相關資訊的鏈接。

For those looking for 'Nepomuk' or 'Baloo' (new generation search in Applications 4.13): technical details can be found on community.kde.org. Read details on the changes for Applications 4.13 here.

簡短說明

如術語提到的，Nepomuk有關數據的分類，組織和表達。它並非是一個應用程序，而是可以被開發人員應用在程序中的組件。

試用

舉例來說，Dolphin採用了 Nepomuk。對於後面例舉的必須保證系統設置-> 桌面搜索的 Nepomuk 和 Strigi 都已經開啟。 Dolphin的信息側面板允許你給文件打上標籤，評分和評論。這些信息隨後存儲在 Nepomuk 並且被 Strigi 編入索引。然後你可以在 Dolphin 裡用導航欄搜索元數據（metadata）。輸入"nepomuksearch:/"，隨後是搜索詞。

功能

Nepomuk 提供數'層'功能給應用程序。第一個也是其中最簡單的是手動標記（manual tagging），評分（rating）和註釋（commenting），如使用在Dolphin中。這有助於你更快的找到你的文件，但這種做法太耗費精力。

為了使得搜索包含文本的文件更容易，Nepomuk 提供了第二個功能：索引（indexing）文件中的文本。它使用一種被稱作Strigi 的技術來實現。現在你也能通過輸入你所已知的其中某些詞語，或僅僅（部分）它們的標題來搜索到文件。

第三層非常複雜，是Nepomuk 被視為歐盟（European union）多個公司和大學研究項目的原因。這部分你會遇到很難理解的詞組像是'語義桌面（semantic desktop）'和'本體論（ontologies）'。基本上，它涉及到語境（context）和關係（relationships）。

Indexing files

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 System Settings -> Desktop Search. 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.

例子

讓我試著用兩個例子解釋Nepomuk 提供了什麼。

關係（Relationship）

假設你2週前從你的某個好友手上收到一張照片。你隨後保存照片到電腦的某個地方。現在你如何找到那個文件哪？如果你不記得保存的位置，你就杯具了（人生是個茶几，你是個杯具）。

現在 Nepomuk 旨在幫助你。你知道這個文件是你朋友發給你的，但你電腦不知道。然而，Nepomuk 能夠記得這個關係。搜索你朋友的名字，隨後便會出現照片哦！

另一個潛在的關係是在你複製出來文本的網頁和你粘貼文本進去的文檔之間，抑或顯示同一輛車的兩幅圖片之間。這樣的關係有時能從文件本身上獲得（你能夠分辨照片，看出誰或什麼東西在那上面）或由關聯的程序（上面E-mail 的例子）提供。 Nepomuk 的這部分還是加緊開發中，需要整合進應用程序，所以你可以期望這功能花費更多年真正實現。切~~( ﹁﹁ )

總之，Nepomuk 的這部分是有關使得搜索智能。試想下Google 是如何智能化你的搜索：當你搜索旅店和城市名，它在網站搜索結果之上顯示google 地圖顯示你提到的那個城市中的各家旅店！它甚至可能推荐一個更適合的名稱以免你犯了拼寫錯誤。 Google 對網站之間的關係（鏈接）使用複雜計算，試著將最相關的信息放置在搜索結果的頂部。 Nepomuk 會能夠提供那樣智能的搜索結果，並用關聯信息根據相關性調整搜索結果。

語境（Context）

這些關係（relationships）不但能幫你搜索文件，也會影響到應用程序及它們提供的信息。注意這種使用Nepomuk 的方式說是設想更恰當而非現實！當中很多組件已經做好，但總體上看都還沒整合進應用程序和桌面。

這裡有個例子講把語境認知（context awareness）帶到桌面上助你工作更有效率。

比如說你正在整理會議上摘的筆記。這時手機響了，某人問你要帶報價的電子表格，還要你根據客戶要求進行修改。再多來幾個打擾後，你會發現整個桌面全是文件和窗口...

如果能更好的組織這一切會非常棒，對嗎？

進入'活動'。之前有在Plasma 中介紹過，當前提供了另類的'桌面'。它們有點像虛擬桌面，但改變的是桌面本身，不是程序集。不同的部件，壁紙之類的東西。當然，自 KDE SC 4.3 後，每個虛擬桌面能夠擁有自個的活動，虛擬桌面和活動是同步的。

如果程序和桌面認識活動，你可以根據經常工作的任務創建活動。所以如果你經常不得不修改帶報價的電子表格，你創建這樣一個活動：擺放一個「文件夾視圖」（或多個）部件到桌面上，添加一個計算器和一個todo 部件來記錄還需要修改的東西。可能需要一個「郵件文件夾」部件來顯示有關報價表問題的郵件！

一旦有人問報價問題，你就切換到這個活動。打開表格程序。表格程序認識你的活動，它的最近打開列表顯示的是報價表格，不是你在另外一個活動工作的存貨清單！ Kopete，這個聊天程序顯示著某個知道有關價格的同事，因為她是你經常在當前這個活動聊天的對象。

等你完成後，你回到另外一個活動，所有程序再一次調整它們的行為來適應你當前的工作。

這樣一個基於活動的工作流程的收益會遠遠超越你最初的期望。它不但能幫你找到文件和聯繫人，還有助於切換任務本身。人腦不擅長多任務-人類切換任務後需要花費幾分鐘來達到正常速度。改變'環境'能大大加快反應，即使只是屏幕上的。把它跟你假日收拾包裹時的情緒對比下！

當然，上面所述很大程度與電腦後頭工作的人是在辦公室還是在家有關。遊戲玩家或臨時用戶可能不太會用到這些活動。

注意上面描述的情節仍舊離現實很遠。基礎的東西在 KDE 中已經有了，但其他部分缺很大。

Frequently Asked Questions

The following is taken from a KDE forums post. Please feel free to add/remove/modify details if you have the time!

What is the Nepomuk Semantic Desktop, and the Strigi Desktop File Indexer?

Nepomuk and Strigi are technologies part of what delivers the abilities of the Semantic Search in KDE. Both are not used directly in the latest generation of KDE's Semantic Search (details), however their successors share much of their code and concepts. Semantic Search provides a way to organize, annotate and build relationships among the data (not only file name and content, but for example which applications used a certain file, or how it is tagged). A number of KDE applications and workspaces use this basic infrastructure to deliver features such as email tagging (KMail) or activity setup (Plasma).

The file indexing allows applications such as Dolphin to search for files based on content, name, or other meta-data (e.g. tags) associated to indexed files. Such an indexer can also index non-text files, such as PDFs, by accessing the meta-data contained in these files (author, publication information, etc.). Some KDE components ship additional "analyzers" for more file types.

Why do we need both Akonadi and Semantic Search? Aren't they doing the same thing?

In short, Akonadi provides a cache of PIM data like calendar items, contacts and email, which is used by applications like KMail and Korganizer but also the calendar build in Plasma. Semantic Search plugs in Akonadi to provide search functionality. How Baloo offers search is actually up to the application. In case of KDE PIM, Xapian is used to provide indexing and search.

How can I disable the semantic desktop?

File indexing can be disabled by adding the users' home folder to the System Settings -> Desktop Search -> Do not search in these locations list. The other functionality is part of the applications that use it and thus can't be disabled without crippling these applications. For example, to not have any search in KMail you'll have to simply remove KMail...

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 Enable Nepomuk File Indexer in the Desktop Search section of System Settings. In case you want to turn off all semantic features, uncheck Enable Nepomuk Semantic Desktop. Notice that this will turn off search in Dolphin as well.

Notice that with the latter option some programs who use Semantic Search for meta-data will offer reduced functionality: for example KMail will not be able to tag mail, or Plasma activities will not offer additional features such as icons, or program data information.

Baloo/Semantic Search is eating 100% CPU! What do I do?

Just wait. Certain files are very hard or even impossible to Index. At the moment, this includes for example text files of over 50 megabyte. When Search finds these, it will try for a fixed time. When it fails, it will try to find out what file is broken and disable indexing it in the future. As it indexes files in batches of about 40, it has to find the problematic file by indexing that bunch in parts: first half/second half, index problematic half in pieces again, until the file is found. This can take up to 30 minutes of heavy cpu usage. Unfortunately, while Baloo will not start to index a new batch of 40 files while on battery power, it continues to determine the broken file while on battery. This behaviour has been fixed in in KDE Applications 4.13.1 (it will stop indexing immediately when the power cord is unplugged) and the time the search for each file can take has been reduced to about 10 minutes. The Semantic Search team is working on improving the indexing tools to handle more difficult files.

Why do I have nepomukservicestub processes even though I've disabled Nepomuk?

It may be a bug. Please file a bug report with a complete description of your problem and the steps to trigger it.

File indexing of PDF/some other file types doesn't work.

PDF indexing is a known issue and it's being tracked in bug #231936. If you have issues with other files, open a bug, preferably adding a sample file that shows the problem.

The program nepomukservicestub crashes at startup.

A large number of fixes for crashes has been fixed for the 4.7.2 release of the KDE Workspaces and Applications. If you encounter more, please file bugs report with detailed instructions on how to reproduce the problem, as sometimes the developers are unable to trigger them in their test setups.

The virtuoso-t process hangs at 100% CPU.

Virtuoso-t is a key component of the old Semantic Search infrastructure and in some occasions the commands sent by the other components end up taking too much time (hence showing the effect of 100% CPU).

Virtuoso is no longer used by Semantic Search starting the Applications 4.13 release.

Sometimes Nepomuk consumes too much RAM.

Many of these problems have been fixed, in other cases however the developers are unable to reproduce the issues correctly. In this case, providing examples and test cases to bug reports increase the chances to get these bugs fixed.

Search accesses the disk too much on startup.

A throttling mechanism implemented in the file indexer, versions after KDE SC 4.8 should no longer have this issue.

My Search database has been corrupted. How do I clean it?

In the extreme case your database is really corrupted and all other attempts have failed, you can delete the $KDEHOME/share/apps/nepomuk directory (where $KDEHOME is usually .kde or .kde4) while Nepomuk is not running. The database will be cleared, but you will also lose existing information such as tags, ratings and comments.

From KDE Applications 4.13 onwards, Semantic Search no longer uses a single, big database, but separate, specialized databases for each type of data. The search databases can be found in $KDEHOME/share/apps/baloo.

Advanced troubleshooting

共享和隱私

在給出其它鏈接前我要指出的是：共享Nepomuk 數據。如果你的標記（tags），評分（ratings）和註釋（comments）能夠在你發送文件給其他人時同時共享給他會很棒。但是,要是你給一個聯繫人打上了“麻煩”的標籤('在床上煩人')，然後發送這個聯繫人的信息給一個共同的好友，但你又不希望這個標籤也一併發送過去...

這個問題當然在考慮之中，是Nepomuk 研究的一個重要課題。由於這些隱私顧慮，外加技術挑戰，所以暫時Nepomuk 內容是私有的。放心，Nepomuk 團隊盡其可能尊重你的隱私。

更多信息：

Wikipedia - Semantic Desktop

Wikipedia - NEPOMUK Framework

NEPOMUK website

NEPOMUK KDE site

article explaining Nepomuk on the DOT

The new Search technology (post KDE Applications 4.13):

The old Search technology: