4 Replies Latest reply: Mar 7, 2013 3:04 PM by Srini VEERAVALLI RSS

    Logical Column Mapping to Multiple Physical?

    chillychin
      I am "learning" OBIEE still and a consultant today showed me something that totally blew my mind

      In the OBIEE Admin tool (in verson 10) there are 3 layers displayed. The physical, business management and presentation layer.

      I was under the impression that columns would be "mapped" one to one from each layer

      The consultant proved me wrong and showed me that in fact, when making a logical column that you can have it "map" to two physical column names

      Since every minute with the consultant is $$$ I tried to google around to find out why and how is this so but havent been able to find anything

      Could someone explain to me why this would be done?

      For example I have the logical column named "Home Faculty" and it is mapped to two physical columns "Faculty Short Desc" & "Main Faculty"

      How would OBIEE know which one to use when?

      Or does it simply "merge" the data between the two columns into one?
        • 1. Re: Logical Column Mapping to Multiple Physical?
          Srini VEERAVALLI
          It can be merge of 2 columns like for FullName concatenation of 2 columns firstName and LastName from 1 or 2 different dimensions.

          If the column is from Fact logical table in BMM then granularity might different and BI know it from Content tab.

          For more details look at this post

          Business Model - Logical Table Source

          If helps mark
          • 2. Re: Logical Column Mapping to Multiple Physical?
            995121
            Hi,

            One logical column can map to multiple physical columns provided its coming from different physical tables. Based on the column taken and joins between the table bi server will know which one to be taken.

            Thanks,
            Phani.
            • 3. Re: Logical Column Mapping to Multiple Physical?
              chillychin
              If one logical column can map to multiple physical columns would it be fair to say that an "equi join" is happening?

              Lets say I have two tables with two columns in the physical layer with the following data

              Table 1

              A1
              A2
              A3

              Table 2

              A1
              A2

              And I map these to one logical column

              If I were to map these two columns to the same logical column what would be the end result of the data?

              Would the logical column then pull data like

              A1
              A2

              Or would it pull everything from Table 1, since it contains all the values of 2 and more?

              Or do the columns have to match?

              Thanks
              • 4. Re: Logical Column Mapping to Multiple Physical?
                Srini VEERAVALLI
                In this case equi join.
                When you are using OBIEE try to see wrt fact table with Table 1 and 2 and follow as I suggest earlier.

                When you use Fact,Table 1 and 2
                Physical Layer Joins would be like:
                Fact join with Table 1
                Fact join with Table 2

                In BMM I can make 3 tables
                Like
                Fact
                dim 1
                dim 2

                Other case would be


                Physical Layer Joins would be like:
                Fact join with Table 1
                Fact join with Table 2

                Table 1's A1,A2 equals Table 2's A1,A2

                In BMM I can make 2 tables
                Like
                Fact
                dim sourcing 1 and 2
                a) 1 mapping with 2
                b) dim with LTS 1 and 2

                Hope this helps
                If I made it more confuse ;) send me email with US mobile# will call you back

                If helps mark