SOA: Joining data across multiple services

Question

Imagine we have 2 services: Product and Order. Based on my understanding of SOA, I know that each service can have its own data store (a separate database, or a group of tables

Answer 1

Another approach would be to have some sort of data source that lives outside of the SOA services. This data source could be considered your cache of the data, your operational data source or even a data warehouse. Extraction packages can export the data from the services (and/or some sort of real time mechanism). You can query this data source how you want.

The advantage of this approach is that the SOA black box is maintained and you can swap out a service knowing how you have coupled it.

Disadvantage is the added complexity and maintenance overhead.