1. A method for sharing data across a legacy application system and a core application system, comprising: identifying a table in the legacy application system containing data similar to data contained in a set of related core application system tables, said legacy application table comprising a substituted table; determining a table structure of each of the substituted table and the set of related core application system tables; defining business logic to remap columns in the set of related core application system tables to corresponding columns in the substituted table based on the table structure of each table; and performing core application system data operations via the business logic that access the remapped columns in the substituted table instead of the columns in the core application system table, wherein the legacy application system is configured to concurrently access the substituted table without requiring any changes to business logic that is used by the legacy application system.