Chronological key is the key which uniquely identifies the data at particular level. chronological key is mostly used in time dimensions where time series functions are used.
Where as logical key is the key which is used to define the unique elements in each logical level.a logical level may have more than one level key. when that is the case, specify the key that is the primary key of that level.it is used to specify the columns which is used for drill down and which is used as primary keys.
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Typically time dimension differs from all other dimensions in one way and that is, all other dimensions don’t care about the order of the values in it.
In region dim the values are north, south, west and east. Here nobody wants to see whether north comes first or south comes first. i.e. no order is required here.
In the case of time dimension there needs to be a particular order for all the values present in it.
e.g. 2010 is earliest and 2004 is older. Dec-10 is earliest and jan-10 is older. i.e. the values in the time dimension needs to follow a particular sorting order. So the chronological key is the key which tells the obiee that the data is incrementing based on the chronological column.
Here you may get another doubt. i.e. you are having columns like year, half_year, quarter, month, week and day. Here which one should become the chronolgocial key?
Analyze it yourself. If you kept year as chro key then obiee will be confused whether jan-10 is earliest or feb-10 is earliest. Because it knows only that 2010 is earliest and 2009 is older.
So always it should be the lowest level of the dimension which needs to be the chronological key. In the above case it should be date.
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