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SWS Documentation on Compilation of aggregates: https://sws.fao.org/doc/docs/statisticalprocesses/cross-cutting/aggregation/
Aggregation module - Reference document (Jan 3, 2024)
Entities
Domains. Thematic (and institutional) datasets. Domains are subject areas such as "TCL. Crops and livestock products".
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Aggregates are set of items. The hierarchical structure provided in an official statistical classification may be used for data aggregation and other, ad-hoc aggregates may be defined for data processing and/or data dissemination purposes. When new aggregates are defined, they are given “new” codes, not present in any official or public statistical classification. E.g., For TCL, "Cereals, primary"