SCD Data Warehousing - Aamir P

Hello Readers! Today we will see about SCD in Data Warehousing.

Slowly Changing Dimensions in Data Warehousing refers to the historical changes that are managed in dimension tables over time. Descriptive information about data in a data warehouse refers to a dimension. SCD tracks changes to this descriptive information. 

The different types of SCD are:-

SCD Type 1 — Overwrite:

Here, there is no tracking of historical changes because the dimension table reflects only the current data. Opt for this when historical data is not important but storage is our only concern. Any change in the dimension table our existing record is overwritten with new information.

SCD Type 2 — Add New Record:

A new table is added to the dimension for every change. Existing records become inactive and new records become current. Use this when historical context is important. 

SCD Type 3 — Add New Attribute:

A limited history is maintained by having multiple columns for the same attribute. So, use this when your concern is limited history and storage means a lot.

Choosing the appropriate SCD type depends on the requirements of the business

So, what are the concerns?

Reporting Requirements: If historical reporting is essential, SCD Type 2 is often the preferred choice.

Storage Constraints: SCD Type 1 or Type 3 may be chosen if storage is a significant concern and historical changes are not critical.

Query Performance: SCD Type 1 generally has the best query performance as it involves updates rather than inserts.

Implementation of SCD involves careful design of the dimension tables, integration with ETL (Extract, Transform, Load) processes, and consideration of how end-users will interact with the data over time.

It’s worth noting that some data warehousing solutions provide built-in support for managing slowly changing dimensions, simplifying the implementation and maintenance of SCD strategies.

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