Creating expressions

Compose allows you to create data transformations in several different places according to your needs. A transformation can either be a filter (i.e. excluding certain data) or an expression (i.e. manipulating a single record). The table below lists the places where transformations can be created and provides reasons for creating the transformation in each of the specified places.

Changes in a dimension expression or lookup of a column in a dimension are not updated retroactively. In order to update historical data, you would need to reload the data which could take a long time depending on the number of records and their history.

Data transformation location comparison
Where the Transformation is Created	Reasons to Create a Transformation There	When the Transformation is Applied
Replicate	Filtering large amounts of data that is not needed for the data warehouse (in the present or the future) Obfuscation due to regulatory reasons or internal policies Data type conversion (e.g. converting a source data type that is not supported on the data warehouse platform)	Before the data reaches the landing zone.
Model	The default location if you are not sure where to put it General business logic Needed for several sources or several data marts	Applied as an update to the staging tables after creating the mappings.
Data Warehouse	Specific source preparation Needed for merging several sources	Between the landing zone and the staging zone.
Data Mart	Specific to a data mart Managed by a data mart data specialist	Between the data warehouse and the data mart.

The following topics describe the Expression Builder:

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