I would like to know what open-source standard XML formats exist for implementing all the data which may be implemented by a personal diary mobile or desktop application (with all possible features you could add already supported by such format). I've searched the internet but didn't find anything. Ideally the formats I'm after would be widely implemented and supported and allow for easy backup of diary data to a server and transfer diary data back and forth between one diary application and another. Of course, the most basic diaries will only need a subset of all the functionality supported by such an XML file format (just a list of dates each with its own plain-text notes).
The following format looks at some of the more basic feature I am looking for in an open interoperable standard XML for diaries file format implementation:
<?xml version="1.0">
<diary>
<day date="2015-03-01">
<entry categories="dream" topics="mary,lunch">
<text>
Today I dreamt about having lunch with mary in the park. At the end I got scared and ran away.
</text>
</entry>
<entry categories="storytelling idea" topics="engineering,flying">
<text>
Today I was walking to school. One thought that came to me was that of a flying bycicle. I came up with everything required to build one. Now I just need to find all the pieces and assemble them.
</text>
</entry>
</day>
<day date="2015-03-02">
<entry categories="thoughts" topics="beach">
<text>
If everybody went to the beach on the very same day, people would be sitting one on top of the other. It would be really crowded!
</text>
<image src="images/beach001.jpg" />
</entry>
</day>
</diary>
If you can't find a dedicated diary standard, consider using a standard XML format for calendars:
You could use description or note fields for the diary entries, and interoperability would be greater than for a proprietary diary format.