Data or Metadata Structure Definition
An SDMX Data Structure Definition (DSD) provides a template which describes the dimensionality of related datasets in terms of their dimensions, attributes and measures.
|Structure Type||Standard SDMX Structural Metadata Artefact|
|SDMX Information Model Versions||1.0, 2.0, 2.1, 3.0|
|URN - DataStructure namespace||urn:sdmx:org.sdmx.infomodel.datastructure.DataStructure|
|URN - Dimension namespace||urn:sdmx:org.sdmx.infomodel.datastructure.Dimension|
|URN - Attribute namespace||urn:sdmx:org.sdmx.infomodel.datastructure.DataAttribute|
|URN - MeasureDimension namespace||urn:sdmx:org.sdmx.infomodel.datastructure.MeasureDimension|
|URN - TimeDimension namespace||urn:sdmx:org.sdmx.infomodel.datastructure.TimeDimension|
Context within the SDMX 3.0 Information Model
Data Structure Definitions (DSDs) are used to describe the structure of datasets by specifying their constituent Components:
and optionally the Representation for each Component.
Each Dataflow references a single DSD which describes the structure of the dataset that the Dataflow represents.
DSD IDs are conventionally uppercase using underscores '_' as separators if required. Examples:
|Eurostat||NA_MAIN||European National Accounts Main Aggregated Statistical Indicators||SDMX-ML|
|IMF||BPO||Balance of Payments and International Investment Position||SDMX-ML|
|IMF||ALT_FISCAL_DSD||Alternate Fiscal Data Structure Definition||SDMX-ML|
|World Bank||WDI||World Development Indicators||SDMX-ML|
The SDMX standard does not preclude using lowercase or mixed case for structure IDs. However IDs are case sensitive meaning that a DSD with ID 'NATIONAL_ACCOUNTS' is distinct from another named 'National_Accounts'.
For Time Series DSDs, the Time Dimension Component is conventionally given the ID 'TIME_PERIOD'.
Data Structure Components
The role of Concepts In defining a DSD's Components
Every Dimension, Attribute and Measure is described by a predefined Concept. Concepts have their own default Representation which can be overridden by defining a Local Representation for the Component in the DSD. That's particularly helpful when using some standard Concepts like the SDMX Cross Domain Concepts where the default Representation is 'String', but the Component needs to be Enumerated or have some use case specific restriction on what values are allowable.
A DSDs Dimensions are the minimal set of statistical concepts capable of uniquely identifying a specific series. For Time Series, the Dimensions in combination with the Time Dimension, uniquely identify an Observation.
In this sense, the Dimensions of a dataset together form its primary key.
Ordering of Dimensions in a DSD
The Dimensions in a DSD have a defined order and together form the dataset's Series Key.
Below is a simple example DSD:
|Position||Component Type||Component ID||Description|
|n/a||Time Dimension||TIME_PERIOD||Observation Time|
|n/a||Attribute||UNIT_MULT||Unit Multiplier e.g. tens, thousands, millions|
|n/a||Attribute||Observation Status||Observation Status e.g. Estimated, Final|
|n/a||Primary Measure||Observation Value||The observation value|
The Series Key is the dot (.) concatenation of the Dimensions in the order specified in the DSD.
For the DSD above, the Series Key is constructed as follows:
ATMCO2.GRC.A ATMCO2.GRC.M TBSINDC.MDG.A TBSINDC.GBR.M
Attributes do not form part of the Series Key so have no explicit or implied ordering.
Attributes allow extra concepts to be added to the dataset to provide additional information about the variable being measured such as the unit multiplier or observation status.
Attributes are unique in that they must be attached to specific levels in the dataset at DSD design time.
All DSDs must have a Primary Measure Component, which is used for the observation value of the main variable being measured. Like all components, the Primary Measure must reference a Concept. For many series, the measure is numeric, but does not need to be so.
A Time Dimension is required for DSDs representing Time Series datasets. Again, the Time Dimension must reference a Concept which should have an appropriate time representation - typically Observational Time Period.
Attribute Attachment Levels
In designing a DSD, attributes must be attached to specific levels in the dataset.
|Dataset||A single value for the attribute is set for the complete dataset|
|Series||A different value for the attribute can be set for each series|
|Observation||A different value for the attribute can be set for each individual observation in a time series|
|Group||A different value for the attribute can be set for a Group of series|
DSDs for Time Series are characterised by having an explicit Time Dimension.
In combination with the DSD's other Dimensions, the Time Dimension uniquely identifies an individual Observation within a Dataset.
Non Time Series
DSDs can be designed for non Time Series datasets by excluding the Time Dimension. This supports use cases like census statistics which, although the observations are from a fixed point in time, there's no sequence of observations over a period of time.
Data Structure Definitions with Multiple Measures
Data Structures can be created in the Registry containing multiple measures, however the generate data set option does not support multiple measures and the load/validation process will reject datasets containing multiple measures.