What Is Type 2 in Data Warehouse?


Heather Bennett

In a data warehouse, the concept of Type 2 is an important aspect of data management. It refers to a method used for handling changes in dimensional data over time. In this article, we will dive into the details of what Type 2 means and how it is implemented.

Understanding Type 2 in Data Warehouse

Type 2 is a technique used to track historical changes to dimensional data in a data warehouse. It allows for the storage of multiple versions or snapshots of a dimension’s attributes over time. This is particularly useful when dealing with slowly changing dimensions (SCDs).

Types of SCDs

Before we delve further into Type 2, let’s quickly touch upon the different types of slowly changing dimensions:

  • Type 1: In this type, there are no historical records kept. The existing values are simply overwritten with new ones.
  • Type 2: This type maintains historical records by creating new rows for every change and keeping track of effective start and end dates for each attribute value.
  • Type 3: In Type 3, only limited history is maintained by adding additional columns to store previous values.

Implementing Type 2

To implement Type 2 in a data warehouse, several steps need to be followed:

  1. Create a Surrogate Key: A surrogate key is an artificial primary key used to uniquely identify each row in a dimension table. This key remains unchanged even when attribute values change.
    • Note: The surrogate key should not be exposed to end-users as it holds no business meaning.
  2. Add Effective Date Columns: Two additional columns, namely “EffectiveStartDate” and “EffectiveEndDate,” are added to the dimension table. These columns help track when a particular attribute value becomes effective and when it expires.
  3. Create New Rows: Whenever there is a change in any attribute value, a new row is inserted into the dimension table with a unique surrogate key, updated attribute values, and appropriate effective dates.
  4. Manage Expiration Dates: To ensure only one row is active at any given point in time, the previous row’s “EffectiveEndDate” is updated to reflect the start date of the new row.

Benefits of Type 2

Type 2 provides several advantages for data warehousing:

  • Historical Analysis: By maintaining historical records, it enables analysis on how attributes have changed over time.
  • Data Integrity: Type 2 ensures data integrity by preserving historical context without overwriting existing values.
  • Flexibility: It allows for easy tracking of changes and provides a comprehensive view of data at any given point in time.

In conclusion, Type 2 in data warehousing plays a crucial role in managing slowly changing dimensions. By implementing this technique, organizations can effectively track changes over time and analyze historical data. Understanding Type 2 is essential for building robust and flexible data warehouses that provide accurate insights into business operations.

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