non-additive facts in a fact table?

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non-additive facts in a fact table?

Post  salaman on Tue Mar 29, 2011 9:43 am

I'm modelling an audio-conversion process where audio files are received and converted into text files.

I have a fact_conversions table, with each row describing a single audio conversion but the only facts in this fact table are audio_length (the length in seconds of the audio file) and conversion_time (the time in seconds it took to convert the audio into text).

Neither of these facts are additive across any dimension but users do want to know things like the average audio_length and the average_conversion time. In order to calculate the averages I'd need to add up the corresponding fact and divide this by the total number of conversions so does this calculation make them additive?

fact_conversions
date_received_key
date_converted_key
language_key
audio_length
conversion_time


Last edited by salaman on Tue Mar 29, 2011 9:48 am; edited 1 time in total (Reason for editing : fixed typos)

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Re: non-additive facts in a fact table?

Post  Dave Jermy on Tue Mar 29, 2011 10:08 am

How are they not additive across the dimensions? You could easily ask for the total audio-length of files in German converted during the first three months of last year.

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Re: non-additive facts in a fact table?

Post  salaman on Tue Mar 29, 2011 10:55 am

Dave Jermy wrote:How are they not additive across the dimensions? You could easily ask for the total audio-length of files in German converted during the first three months of last year.

I see your point. Technically they are additive but I never looked at it in that way because the business would never be interested in total audio-length. But I guess just because the business aren't interested in it doesn't mean it's not additive.

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