Sunday, November 23, 2008

On the rain in the window -- windows and temporal contexts

I realized that I have not written for a while, I am not out of topics, just trying to do too many things in parallel... Anyway, I am typically late in changing from summer clothing to winter clothing relative to most others, but it happened yesterday, maybe the noise of the heavy rain in the window, brought me to change from short shirt and sandals to long shirt and shoes.
Winter is a relative term, people who live in some climates, will not call our winter as winter.

Last night I attended the conclusion session of "students exchange trip" in which my 13 years old daughter Hadas has participated, they visited a school in Foster City, California, this is a plan called "ambassadors", and they had also to give speeches about various aspects on Israel, one of their challenges was to convince their host to come to Israel as a counter-visit. Since the international media create the preconception that Israel is a dangerous place to be, with wars in the streets etc.., some people (typically those who have never been here) are afraid to come... It seems that the children were successful to convince that in Haifa we live normal life, and there is no war in the streets... Actually I am used to people I ask me, that I feel much safer in Haifa then in New-York, London, or Paris. Paris is the only place I was attacked by thieves, so it is the most terrifying city for me.

Back to the rain in the window. The notion of "window" that came from stream processing, is used to process a sub-stream that is bounded by time (or by number of occurrences). In some cases a window can be specified by some starting time and duration, or slide at certain time intervals, however, in other cases we need to process events in a time interval "while it is raining" - this is done either to find certain patterns that are only relevant in raining time, or use the stream processing classic application --- aggregate within a sub-stream. In any case, this is not determined by fixed time, and the duration is not known in advance. This can be either "while something is in state S" or a time interval that starts by the occurrence of event E1 and ends by the occurrence of event E2. An interval may also expire if the state lasts too long...

I'll re-visit the notion of context and its formal definition soon.

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