1. A method for sharing data across a legacy application system and a core application system, comprising: identifying a legacy application table in the legacy application system based on data contained in a set of related core application system tables of a set of core application system tables, wherein the set of core application system tables are associated with a business component, the set of core application system tables comprise one or more columns that are not part of the set of related core application system tables or the legacy application table, the one or more columns in the set of core application system tables are required by the core application system, the legacy application table comprises a portion, the portion corresponding to a substituted table, and the portion is configured to be used by the core application system; determining a structure of the portion and the set of related core application system tables; mapping columns in the set of related core application system tables to corresponding columns in the portion based on the structure of the portion and the set of related core application system tables, wherein as a result of the mapping, the portion comprised in the legacy application table is accessible by both the core application systems and the legacy application system; and determining that core application system data operations have been previously configured to access the columns in the set of related core application system tables; performing the core application system data operations such that the core application system data operations access the mapped columns in the portion comprised in the legacy application table instead of the columns in the set of related core application system tables, wherein the legacy application system is configured to concurrently access the portion, and the core application system is configured to concurrently access the one or more columns in the set of core application system tables.