One of the main advantages of the XML format is that the data is separated from its visual presentation. The bottom part of Figure 4 presents XML data for the Patient demographics and record parameters. The upper part of the Figure 4 is the same data transformed by an XSLT template and rendered in Internet Explorer. It is worth to mention also that because XML format is compatible with existing database systems, all SleepXML data can be readily stored into existing databases (e.g. an SQL database containing patient information and questionnaire data).



Figure 4. Patient data in XML form and its HTML presentation Web-compatible presentation of the physiological signals has not been forgotten. SleepXML does convert waveform and event visual display to the SVG format to be rendered in a Web browser. SVG stands for the Scalable Vector Graphics, a royalty-free vendor-neutral open standard developed under the W3C Process for interactive two-dimensional graphics [6]. Figure 5 presents a page of PSG data (taken from PhysioBank data collection [5]) displayed in Internet Explorer.


Figure 5. PSG waveform data segment presented in SVG format and rendered by a Web browser. It is worth to mention that being a vector graphics standard, SVG allows interactive manipulations of the waveform display, such as changing the waveform amplitudes or chart speed, as well as turning off and on the events display. Such kind of interactivity is not available in raster picture formats, such as JPG or PNG.