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ICT Skills 1

Do you know how to compress and decompress files? (21/31)

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[DE: Datei komprimieren]
File compression

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File compression

File compression (also known as packing) refers to the process of converting a large file (or group of files) into a smaller file that requires less space than usual. Decompression or extraction is the opposite process, that is, using the compression program to restore the compressed files to their original size.

 

Strategies

There are different strategies for compressing a file: the lossless compression and the lossy compression. The former implies that no data is lost and therefore the process is fully reversible. The latter implies that some data is lost, and that the process is not fully reversible. Although lossy compression allows you to create smaller files than with lossless compression, many files lose their functionality when undergoing lossy compression.

Algorithms

File compression is possible thanks to the use of algorithms (COmpression DECompression algorithms - CODECs) that enable users to convert a bit string into a shorter one. For example, a bit string such as the following "12/56/177, 12/56/177, 12/56/177, 12/56/177" would look like "5 times 12/56/177" when compressed.

Compression rates

The compression rate in general depends on the type of data. Normally, text files can be compressed by up to 40%, executable programs by up to 50%, and images by between 5% and 60%. Some examples of compression formats and encoding are: JPEG (which stands for Joint Photographic Experts Group), MPEG (short for Moving Pictures Expert Group), ZIP/TAR and BinHex (for Macintosh). The most common compression/decompression programs are: Winzip, WinRAR, WinAce, ARJ, LHarc, PkZip, Gunzip, tar and unzip. Many of them can be freely downloaded  from the Internet.

How to compress a file?

To compress a file, right-click on it and select one of the following options:

  1. Send to Compressed Folder: by using this option you create a compressed folder in the current location
  2. Add as "File_Name.zip" or "File_Name.rar": a new compressed file is created in the current location having the same name as the original file and a different file extension (for example .zip or .rar)
  3. Send to compressed folder and via email: a folder structure containing your file will be created, then compressed under the name you choose and finally sent via email
  4. Send to compressed folder "File_Name.zip" and via email: a folder structure containing your file will be created maintaining the same name as the original file and then sent via email

How to extract a compressed file?

To extract a compressed file, right-click on it and select one of the following options:

  1. Extract file: when selecting this option, a dialog box opens for you to select the location where you want to save the extracted file. In the window you can specify some other options regarding file updating ("extract file and overwrite", "extract file and update", etc.), file overwriting ("ask before performing the task", "without confirmation", etc.), etc. This option is useful if you want to save your file in a different location than the current one
  2. Extract here: this option allows you to extract the compressed file directly in its current location
  3. Extract in \: when choosing this option the compressed file will be extracted also under the current location but in a folder under the same name as the file

Why is this information important for translators and translation teachers?
Today, translators receive their translation material most commonly via email or on storage devices such as DVDs, CDs, flash drives, diskettes, etc. Sometimes, when the files to be translated are too large to fit on the storage devices, clients or translation agencies have to compress them. Also, when there are several files to be delivered to the translator - such as the files to be translated plus graphics, reference texts, translation memory files, databases, etc. - clients or translation agencies compress the files and create archives.

In these cases, translators have to know how to extract the files with or without altering the original folder structure (depending on the client's or agency's specifications) and also how to compress the translated files once these are ready, in order to deliver the translation to the client/translation agency as it was received.

 

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