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      Standard Annotation Format

The creation of a new format called Standard Annotation Format (abbreviated SAF) is a direct consequence of using a more complete annotation scheme in EDF++ files. More complete -- and thus more verbose – annotations need of course more place. For compatibility with most EDF/EDF+ readers, an annotation should be placed in the record covering the time window during which the annotated event occurred. Thus, when some record contains many annotations or some long annotations, a large space must be reserved within the record structure to save these information. However, this large space is constant across records, although other records in the file might contain essentially no annotations. This causes increasingly large waste of memory as annotations become more verbose or numerous. This problem is event more acute with long recordings such as in sleep study.


In such a situation, compressing EDF++ annotation files can generally reduce their size by more than 95%. Thus, it was decided to share only compressed annotation files. However, this is obviously not a perfect solution since it requires the MASS users to decompress these large files containing mostly zeros. For this reason, we also provide annotations in another format which we called Standard Annotation Format (SAF). This format is actually very simple. SAF files contain only a sequence of TAL annotations as defined in the EDF+ standard. It does not contain any file header and it is not segmented in records as usual EDF files.


Note 1. Since no headers are provided, SAF files must always be associated with an EDF/EDF+/EDF++ files to determine absolute timing of their annotations.


Note 2. A sequence of TAL annotations has been adopted to make it as simple as possible to modify existing EDF readers to read SAF files.




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