C.1. Structural metadata: Balance of Payments-Data Structure Definition
18.23. Structural metadata contain the list of concepts and attributes of variables necessary to codify the reporting requirements of four international agencies, the European Central Bank (ECB), Eurostat, the International Monetary Fund (IMF) and the Organization for Economic Cooperation and Development (OECD),  for data collection exercises of external sector statistics, including international trade in services. The Balance of Payments-Data Structure Definition (BOP-DSD) structure is based on the methodology defined in the IMF Balance of Payments and International Investment Position Manual, 6th edition (BPM6), MSITS 2010, and the OECD Benchmark Definition of Foreign Direct Investment, 4th edition (BD4). In order to code trade in services data, the Extended Balance of Payments Services Classification (EBOPS), including the complementary groupings, is included in the “international account item” dimension of the DSD.
18.24. The BOP-DSD, presented on the SDMX website, includes 16 concepts and 13 attributes (see box 18.2). Concepts are used to uniquely identify a time series and, when joined together, provide the series code or “time series keys,” which are the unique identifiers for a time series. When defining a time series key using SDMX, a valid code must be assigned to each concept of the DSD. Attributes are used to further describe the data.
18.25. When coding detailed trade in services by partner country statistics, a number of BOP-DSD concepts are fixed, e.g., the reference and counterpart sectors are defined as the total economy (S1) when the data refer to total trade between related and unrelated parties. However, trade in services between related parties can also be coded by using code S1A “affiliates”, in the counterpart sector dimension, whereas S1B should be used for unaffiliated parties.
18.26. Other concepts of the DSD are not fixed, such as the “counterpart area”, which is used to identify the territory of the non-resident entity of individual time series. The country code list in the counterpart area follows the International Organization for Standardization (ISO) classification and is a “cross-domain” code list. The codes used for various regional groupings were harmonized across international agencies that use the BOP-DSD, wherever possible.
 The four agencies are the European Central Bank, Eurostat, IMF and OECD.
 At the time of writing, there is not yet a data structure definition (DSD) available neither for FATS nor for non-monetary indicators of modes of supply. A FATS DSD would include specific dimensions such as FATS characteristics, e.g., number of enterprises, number of persons employed, etc. and resident economic activity vs. non-resident economic activity. Items specific to non-monetary indicators on modes of services supply would include direction of trips: inbound, outbound; and country of origin or destination.
 In order to eliminate the possibility of having multiple ways of coding the EBOPS 2010 complementary grouping “total services transactions between related entities”, that item is not coded in the international accounts dimension of the DSD, but is coded in the annual international trade in services dataflow as follows (example on the credit side): A.N.#.%.S1.S1A.T.C.S._Z._Z._Z.$._T._X.N.