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The aggregation pattern is considerably valuable if you when we are creating orchestration APIs to “modernize” legacy systems, . This is especially true when you we are creating an API that gets extracts data from multiple systems , and then processes it merges that data into one response. Another use case is creating reports or dashboards that pull extract data from multiple systems, aggregate its measures and create an interactive experience with that data.
Finally, you we may have multiple systems that you use used for compliance or auditing purposes that need to have extract related data from multiple systems. The aggregation pattern is helpful in ensuring that your compliance data lives in one system but can be the amalgamation of relevant data from multiple systems. You can therefore reduce the amount of learning that needs to take place across the various systems to ensure you have visibility into what is going on.