Information systems are meant to automate the repetetive tasks of the employees of your business. Systems administer data relevant to it's business owners and users (E.g.: people, places, things, events and reasons). Designing these systems requires lists of datamodels, proces models, database models, schemas and diagrams with object classes, procedures, documentation sets, and lots more.
The Zachman Framework (wikipedia: link) covers these systems and business areas. CaseTalk fits very well in the "What/Data" area of the Zachman framework. Below is a diagram which illustrates this specific what-are from a CaseTalk perspective.
See also the layering of models.