In traditional relational databases, Slowly Changing Dimensions (SCDs) are a common problem when dealing with changing entity attributes over time. However, NoSQL databases, like MongoDB, Cassandra, or DynamoDB, present unique challenges when it comes to handling SCDs due to their schema-less nature. In this blog post, we will explore some techniques to handle slowly changing dimensions in NoSQL databases.

1. Versioning Approach

One approach to handle SCDs in NoSQL databases is to use a versioning approach. In this technique, instead of updating existing documents, a new version is created each time an entity’s attribute changes. This ensures that the historical data is preserved and can be queried later.

Here’s an example of how this can be implemented in MongoDB:

{
  "_id": ObjectId("5fe4a9c79370b80e91e4e488"),
  "product_id": "123",
  "name": "Product A",
  "price": 50,
  "version": 1,
  "timestamp": ISODate("2020-12-24T12:00:00Z")
}

When the name of “Product A” changes, a new document is inserted with an incremented version number and a new timestamp.

2. Document Embedding

Another technique is to use document embedding, where each document represents a snapshot of the entity at a specific point in time. This approach is particularly suitable for NoSQL databases where denormalization is common practice.

For instance, in a Cassandra database, you can use a variation of the Wide Column Store pattern to store historical data:

CREATE TABLE products (
  id text,
  timestamp timestamp,
  name text,
  price double,
  PRIMARY KEY (id, timestamp)
);

By including the timestamp in the primary key, you can store multiple versions of the same entity, allowing you to retrieve historical records easily.

Conclusion

Handling slowly changing dimensions in NoSQL databases requires careful consideration based on the specific feature set of the chosen database. By using versioning approaches or document embedding techniques, you can effectively manage changing entity attributes while preserving historical data.

#NoSQL #SCD