A composite domain is a logical grouping of individual Domains. Often single domains cannot be validated alone or need additional context for an exact validation.
If, for example, you want to validate a postal code for Germany, you can work with different rules such as a defined length, you can also store all postal codes of Germany in one domain. For a reasonable validation, however, you also need the street name, house number and city in the rules.
If you not only want to validate data but also enrich it, you need different domains that represent the input data and domains in which the enriched data can be stored. For example, you can define the domains Street, Postalcode, City, Country as well as Latitude and Longitude for a geodata enrichment.
You map these functionalities via Composite Domains. In the current version, you can combine a Composite Domain with various Reference Data Services to perform validations and enhancements.
Business Rules within a Composite Domain are on the current roadmap of HEDDA.IO.