What is the difference between TestCase Design and the Test Data Service ?

TCD - Test Case Design can be thought of as a design mechanism, which structures TestCases strategically to include all the variants and pathways for the SUT. Some static data values can be added, but this data is non-consumable, that is it can be used multiple times and simultaneously. 

Note - TestCase Design Stractures TestCases Startegically to include all different variants for the SUT. 

Some static and non-consumable data.

TDS - Test Data Service, acts as a data repository, where data can be stored, retrieved and updated and its status easily viewed by multiple people. Furthermore, TDS stores consumable or dynamic data that regularly changes. This data can generally only be used once and by one machine at a time.

Note- TestData Service acts as a data repository. 

Consumable and dynamic data.