Overview
ISO/IEC 19075-8:2021 - "Information technology - Guidance for the use of database language SQL - Part 8: Multidimensional arrays" provides guidance on defining and using multidimensional arrays (MD-arrays) in SQL. The standard explains the syntax and semantics for the SQL/MD-array data type as defined in ISO/IEC 9075-15, positioning arrays as first-class data types for Big Data, scientific and engineering applications. It documents the data model, creation and update mechanisms, array operations, exporting/encoding, and realistic examples (notably a remote sensing use case).
Key topics and technical scope
- MD-array data model: concepts such as MD-axis, MD-extent, MD-dimension (rank), coordinates and cardinality; how array values are represented and typed.
- Type and creation rules: MD-array typedefinition, element types, axis names and limits; multiple construction methods (explicit enumeration, table-to-array conversion, iteration, decoding encoded formats).
- Update and storage semantics: guidelines for updating arrays, handling arrays with differing dimensions and single-element updates.
- SQL/MDA operations: a catalog of operations including subsetting, reshaping, shifting, axis renaming, scaling, concatenation, induced operations, join-on-coordinates, and aggregation; extent probing and element referencing are also covered.
- Import/export and encoding: recommendations for ingesting array data, converting arrays to/from table representations and serial formats (e.g., JSON examples).
- Practical examples: a detailed remote sensing example (band math, NDVI, histograms, change detection, feature extraction) illustrating querying and processing of MD-arrays in SQL.
Applications and who should use it
ISO/IEC 19075-8:2021 is directly relevant to:
- Database implementers and vendors extending SQL engines with array datatypes and operators.
- Data engineers and architects designing data platforms that integrate relational and multidimensional data.
- GIS, remote sensing and imaging specialists who process raster and multiband imagery (examples in the standard include NDVI and band operations).
- Scientific computing, IoT and ML practitioners handling tensor-like time-series, sensor grids, and multidimensional simulation outputs.
- Analysts needing integrated querying of relational and array data for Big Data workflows.
Practical benefits include streamlined ingestion of array data, unified SQL-based querying and transformations, improved interoperability with ISO/IEC 9075 SQL parts, and clearer semantics for array manipulation in analytics pipelines.
Related standards
- ISO/IEC 9075-15 (SQL/MDA) - defines the MD-array datatype referenced by this guidance
- ISO/IEC 9075 series (SQL framework & foundation) - provides the broader SQL framework and foundation standards
- ISO/IEC 19075 series - companion guidance on SQL usage
Keywords: ISO/IEC 19075-8:2021, SQL multidimensional arrays, MD-array, SQL/MDA, ISO/IEC 9075-15, Big Data, array operations, remote sensing, NDVI.
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