It is a dimension which is shared by multiple fact tables
Ex: customer dimension, time dimension
It is a process of connecting multiple fact tables with PK-FK relationship
Slowly changing dimension (SCD)
A slowly changing is a dimensions which captures the changes occurs over a period of time
- there are three types of SCD’s
- SCD type1
- SCD type 2
- SCD type3
SCD type 1
It contain only current data
SCD type 2
It maintain couple history and current data
SCD type 3
It maintain partial history (or) recent history and current data
It is a system generated key which access primary key in the dWH tools maintains the uniqueness.
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OLAP and types of OLAP
It is a interface (or) a gate way between the user and data source (dWH)
It is a set of specifications with allows the client application (report application) to query the data from data source and displays the data and to report
Types of OLAP
- DOLAP (desk top)
- ROLAP (relational)
- MOLAP(multi dimensional )
It is a OLAP used to query the data from desktop database like Dbase, fox, ms access, ckpper. While generating the report online
It is used to query the data from multidimensional source like cube and DMR model (dimensional relational model) to perform multidimensional analysis.
Multi dimensional analysis
It is a process of viewing the data at different levels of details
- Use the following features to perform multidimensional analysis
Navigating from lowest level to highest level
Navigating from highest level to lowest level
It is a combination of both ROLAP and HOLAP it can query the data from the relational sources as well as multi dimensional sources like cognas.
Phases in dimensional modeling
- Conceptual modeling
- Logical modeling
- Physical modeling
In conceptual modeling face, database models conform or decide the dimensional tables and fact tables required for a particular data ware house design.
In logical modeling database modelers start creating relation between the tables logically
In physical modeling database modelers creates dimensional tables and fact with relations physically in the database
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