This part of ISO 20022 was prepared to complement ISO 20022-1. The reverse engineering guidelines explain how to extract relevant information from existing IndustryMessageSets in order to prepare the submission to the ISO 20022 Registration Authority of equivalent, ISO 20022 compliant BusinessTransactions and MessageSets. The ISO 20022 Repository will contain all ISO 20022 compliant BusinessTransactions and MessageSets, as outlined in ISO 20022-1. The approach to be followed for adding ISO 20022 compliant BusinessTransactions and MessageSets to the Repository can be classified according to the following scenarios. Case 1: No ISO 20022 compliant BusinessTransactions and MessageSets exist. No IndustryMessageSet exists. EXAMPLE Collective Investment Vehicles. Approach: full development of ISO 20022 compliant BusinessTransactions and MessageSets using ISO 20022-3. Case 2: No ISO 20022 compliant BusinessTransactions and MessageSets exist. One or more IndustryMessagesets exist. EXAMPLE Securities Pre-Trade (FIX MessageSet exists). Approach: conversion of the IndustryMessageSet(s) into ISO 20022 compliant BusinessTransactions and MessageSets, using ISO 20022-5. c) Case 3: ISO 20022 compliant BusinessTransactions and MessageSets exist. One or more existing IndustryMessageSets exist as well. EXAMPLE Securities Post-Trade (FIX, Omgeo MessageSets exist). Approach: comparison of the existing IndustryMessageSet(s) with the ISO 20022 compliant BusinessTransactions and MessageSets and extension of the ISO 20022 compliant BusinessTransactions and MessageSets as necessary, using ISO 20022-5. This part of ISO 20022 describes the activities of ISO 20022 reverse engineering from the point of view of the user who wants to verify that the business functionality, covered by his own IndustryMessageSet, is covered by ISO 20022 compliant BusinessTransactions and MessageSets. The intention of this part of ISO 20022 is not to attempt to define a “methodology” for reverse engineering. It describes the following set of required activities. 1) Extract relevant information from existing IndustryMessageSets and compare it to the related information in the ISO 20022 Repository. 2) Use the results of this comparison for the development of ISO 20022 compliant BusinessTransactions and MessageSets. 3) Submit the resulting update requests to the Registration Authority. NOTE It is not the intention of reverse engineering to systematically create ISO 20022 compliant versions of all existing IndustryMessageSets. Update requests are always based on a valid business justification. 1. 4) Prepare the migration to the ISO 20022 compliant BusinessTransactions and MessageSets. The main objectives of this part of ISO 20022 are to: capture the industry knowledge covered by existing IndustryMessageSets; build upon former standardization efforts in the industry when building ISO 20022 compliant BusinessTransactions and MessageSets; ensure that the resulting ISO 20022 compliant BusinessTransactions and MessageSets cover fully the business scope of existing IndustryMessageSets; maximize interoperability between existing IndustryMessageSets and ISO 20022 compliant BusinessTransactions and MessageSets; support the migration from existing IndustryMessageSets to ISO 20022 compliant BusinessTransactions and MessageSets.