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The term round-trip is commonly used in document conversion particularly involving markup languages such as XML and SGML. A successful round-trip consists of converting a document in format A (docA) to one in format B (docB) and then back again to format A (docA′). If docA and docA′ are identical then there has been no information loss and the round-trip has been successful. More generally it means converting from any data representation and back again, including from one data structure to another. ==Information loss== When a document in one format is converted to another there is likely to be information loss. For example, suppose an HTML document is saved as plain text ( *.txt). Then all the markup (structure, formatting, superscripts, …) will be lost. Compound documents will frequently lose information on images and other embedded objects. If the text file is converted back to the original format, information will necessarily be missing. A similar effect happens with image formats. Some formats such as JPEG achieve compression through small amount of information loss. If a lossless file, such as a BMP or PNG file, is converted to JPEG and back again then the result will be different from the original (although it may be visually very similar). Just because the initial and final documents are not bitwise identical does not mean there is information loss. Some formats have undefined fields, or fields where the contents have no impact on the result. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Round-trip format conversion」の詳細全文を読む スポンサード リンク
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