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sql server data warehouse : Large Slowly Changing Dimension
I'm somewhat new to data warehousing, and have some basic questions. Let's say I have a fact table, named sales. The financial analyst would like to be able to sort the sales information based on several customer related attributes. Some of these attributes would include zip code, age, and income. While I can create a customer dimension, these attributes change over time. The analysts are really only interested in these customer attributes at the time of the sale. For example, they only care about where a customer lived at the time of the sale, but not where they are living now. Now I know there are different techniques for dealing with changing dimensions, but I'm left with the impression that it would be making things more complicated then necessary. Would it not be best to just simply store this information in the fact table itself? While I'm aware that fact tables are primarily used to store numerical information, I don't see the advantage of putting this information in a separate dimension. Your input would be much appreciated. Thanks,
Hi,
You say the analysts are interested in the customer attributes at the time of the sale. So these attributes will have to be stored in dimensions to be able to analyse them using datawarehouse techniques. These must be slowly changing. So when you add more salesfacts, e.g. with a zipcode that doesnt exist in the zipcode dimension yet, you'll have to add it to the dimension. The alternative is to drop and recreate all the facts and dimensions, but that's no option if the customers move or the incomes change in the source system. Good luck... Jeroen. [quoted text, click to view] "Attila" <ThisIsAFakeAddress35@hotmail.com> wrote in message news:9516751f.0401290847.23e49471@posting.google.com... > Hello, > > I'm somewhat new to data warehousing, and have some basic questions. > Let's say I have a fact table, named sales. The financial analyst > would like to be able to sort the sales information based on several > customer related attributes. Some of these attributes would include > zip code, age, and income. While I can create a customer dimension, > these attributes change over time. > The analysts are really only interested in these customer attributes > at the time of the sale. For example, they only care about where a > customer lived at the time of the sale, but not where they are living > now. Now I know there are different techniques for dealing with > changing dimensions, but I'm left with the impression that it would be > making things more complicated then necessary. > Would it not be best to just simply store this information in the > fact table itself? While I'm aware that fact tables are primarily used > to store numerical information, I don't see the advantage of putting > this information in a separate dimension. > Your input would be much appreciated. > > Thanks, > Attila
[quoted text, click to view]
> So these attributes will have to be stored in dimensions to be able to analyse them using datawarehouse techniques.Can you elaborate on this part? What specifically will an analyst not be able to do if I store the customer data in the fact table? Thanks, Attila [quoted text, click to view] "Spike" <jeroenaNOSPAM@hotmail.com> wrote in message news:<bvgf14$sjl$1@reader08.wxs.nl>...
> Hi, > > You say the analysts are interested in the customer attributes at the time > of the sale. So these attributes will have to be stored in dimensions to be > able to analyse them using datawarehouse techniques. These must be slowly > changing. So when you add more salesfacts, e.g. with a zipcode that doesnt > exist in the zipcode dimension yet, you'll have to add it to the dimension. > > The alternative is to drop and recreate all the facts and dimensions, but > that's no option if the customers move or the incomes change in the source > system. > > Good luck... > Jeroen. > > "Attila" <ThisIsAFakeAddress35@hotmail.com> wrote in message > news:9516751f.0401290847.23e49471@posting.google.com... > > Hello, > > > > I'm somewhat new to data warehousing, and have some basic questions. > > Let's say I have a fact table, named sales. The financial analyst > > would like to be able to sort the sales information based on several > > customer related attributes. Some of these attributes would include > > zip code, age, and income. While I can create a customer dimension, > > these attributes change over time. > > The analysts are really only interested in these customer attributes > > at the time of the sale. For example, they only care about where a > > customer lived at the time of the sale, but not where they are living > > now. Now I know there are different techniques for dealing with > > changing dimensions, but I'm left with the impression that it would be > > making things more complicated then necessary. > > Would it not be best to just simply store this information in the > > fact table itself? While I'm aware that fact tables are primarily used > > to store numerical information, I don't see the advantage of putting > > this information in a separate dimension. > > Your input would be much appreciated. > > > > Thanks,
I suggest reading articles written by Ralph Kimball. Here's one of his
classic articles on slowly changing dimensions. http://www.dbmsmag.com/9604d05.html [quoted text, click to view] "Attila" <ThisIsAFakeAddress35@hotmail.com> wrote in message news:9516751f.0402020643.36d448b7@posting.google.com... > > So these attributes will have to be stored in dimensions to be > able to analyse them using datawarehouse techniques. > > Can you elaborate on this part? What specifically will an analyst not > be able to do if I store the customer data in the fact table? > > Thanks, > Attila > > > "Spike" <jeroenaNOSPAM@hotmail.com> wrote in message news:<bvgf14$sjl$1@reader08.wxs.nl>... > > Hi, > > > > You say the analysts are interested in the customer attributes at the time > > of the sale. So these attributes will have to be stored in dimensions to be > > able to analyse them using datawarehouse techniques. These must be slowly > > changing. So when you add more salesfacts, e.g. with a zipcode that doesnt > > exist in the zipcode dimension yet, you'll have to add it to the dimension. > > > > The alternative is to drop and recreate all the facts and dimensions, but > > that's no option if the customers move or the incomes change in the source > > system. > > > > Good luck... > > Jeroen. > > > > "Attila" <ThisIsAFakeAddress35@hotmail.com> wrote in message > > news:9516751f.0401290847.23e49471@posting.google.com... > > > Hello, > > > > > > I'm somewhat new to data warehousing, and have some basic questions. > > > Let's say I have a fact table, named sales. The financial analyst > > > would like to be able to sort the sales information based on several > > > customer related attributes. Some of these attributes would include > > > zip code, age, and income. While I can create a customer dimension, > > > these attributes change over time. > > > The analysts are really only interested in these customer attributes > > > at the time of the sale. For example, they only care about where a > > > customer lived at the time of the sale, but not where they are living > > > now. Now I know there are different techniques for dealing with > > > changing dimensions, but I'm left with the impression that it would be > > > making things more complicated then necessary. > > > Would it not be best to just simply store this information in the > > > fact table itself? While I'm aware that fact tables are primarily used > > > to store numerical information, I don't see the advantage of putting > > > this information in a separate dimension. > > > Your input would be much appreciated. > > > > > > Thanks, > > > Attila
There is an entire chapter in Ralph Kimballs book on mini dimensions,
which help to stabilise the pain of rapidly changing dimensions. Ashish On Tue, 17 Feb 2004 15:29:51 -0500, Domenico Discepola [quoted text, click to view] <domenico_discepola@quadrachemicals.com> wrote: > I suggest reading articles written by Ralph Kimball. Here's one of his > classic articles on slowly changing dimensions. > > http://www.dbmsmag.com/9604d05.html > > > "Attila" <ThisIsAFakeAddress35@hotmail.com> wrote in message > news:9516751f.0402020643.36d448b7@posting.google.com... >> > So these attributes will have to be stored in dimensions to be >> able to analyse them using datawarehouse techniques. >> >> Can you elaborate on this part? What specifically will an analyst not >> be able to do if I store the customer data in the fact table? >> >> Thanks, >> Attila >> >> >> "Spike" <jeroenaNOSPAM@hotmail.com> wrote in message > news:<bvgf14$sjl$1@reader08.wxs.nl>... >> > Hi, >> > >> > You say the analysts are interested in the customer attributes at the > time >> > of the sale. So these attributes will have to be stored in dimensions >> to > be >> > able to analyse them using datawarehouse techniques. These must be > slowly >> > changing. So when you add more salesfacts, e.g. with a zipcode that > doesnt >> > exist in the zipcode dimension yet, you'll have to add it to the > dimension. >> > >> > The alternative is to drop and recreate all the facts and dimensions, > but >> > that's no option if the customers move or the incomes change in the > source >> > system. >> > >> > Good luck... >> > Jeroen. >> > >> > "Attila" <ThisIsAFakeAddress35@hotmail.com> wrote in message >> > news:9516751f.0401290847.23e49471@posting.google.com... >> > > Hello, >> > > >> > > I'm somewhat new to data warehousing, and have some basic questions. >> > > Let's say I have a fact table, named sales. The financial analyst >> > > would like to be able to sort the sales information based on several >> > > customer related attributes. Some of these attributes would include >> > > zip code, age, and income. While I can create a customer dimension, >> > > these attributes change over time. >> > > The analysts are really only interested in these customer attributes >> > > at the time of the sale. For example, they only care about where a >> > > customer lived at the time of the sale, but not where they are >> living >> > > now. Now I know there are different techniques for dealing with >> > > changing dimensions, but I'm left with the impression that it would >> be >> > > making things more complicated then necessary. >> > > Would it not be best to just simply store this information in the >> > > fact table itself? While I'm aware that fact tables are primarily >> used >> > > to store numerical information, I don't see the advantage of putting >> > > this information in a separate dimension. >> > > Your input would be much appreciated. >> > > >> > > Thanks, >> > > Attila > > --
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