Kindle Notes & Highlights
Started reading
September 2, 2019
this book to study for the exam
The surrogate key value in a dimension table acts as the table’s primary key and is typically auto-generated when the table is loaded.
Surrogate key
Alternate keys are the unique identifiers of the dimension members in the LOB application database system. Typically, they are the primary key in the LOB source system tables and are also referred to as the business key or candidate key.
Alternative Key
In addition to key columns, dimension tables also include other attribute columns that are typically used for filtering and as rows or columns in reports.
Attribute Column
The fourth type of dimension columns are metadata columns. These columns are used internally in data warehouse ETL (or ELT) operations and processes.
Metadata
Dimensions can be shared across many analysis in the data warehouse. For example,
The calendar hierarchy is an example of a natural hierarchy because each attribute can be related to another in a natural order.
Natural hierarchy
Hierarchies that do not follow a natural order are considered unnatural hierarchies.
Unnatural hierarchy
the requirement of keeping track of changes of dimension values over time for historical reporting is commonly delegated to the data warehouse and is known as the Slowly Changing Dimension (SCD) concept.
Slowly changing dimension
Type 0 SCD is a misnomer because this type of SCD ignores changes to attribute values.
SCD type 0
Type 1 SCD tracks changes by overwriting the current attribute value.
SCD type 1
Type 2 SCD tracks changes by inserting a new record with the changed values and keeping the old record with the original attribute values.
SCD 2
Dimension keys are required to create table relationships in a data warehouse.
Dimension key
