This deliverable defines data specifications and a data model for the 3PhaseInsight project, providing a shared technical and semantic understanding of the three-phase smart meter dataset delivered by Radius. It establishes standardised definitions for topology data (e.g., substations, transformers, feeders, and cables) and time-series measurements (e.g., voltage, active/reactive power, and harmonic distortion per phase), along with their naming conventions and relationship mappings across entities. The specification integrates multiple data sources, including raw CSV files, supplementary metadata, and additional contextual attributes, into a framework that supports accurate interpretation, data quality management, and alignment across project partners. Building on this specification, the deliverable proposes a scalable hybrid data model that combines relational databases for structured grid topology and metadata with object storage for large-scale time-series data. The model introduces versioned topology graphs to capture grid network changes over time, thereby enabling traceability and reproducibility of analytical results, while metadata structures support data lineage, ingestion tracking, and storage of algorithm results. Measurements are stored in partitioned, columnar formats to ensure efficient querying at scale. These combinations lay a solid foundation for pipeline development, thereby positioning the data model as a central enabler of the project's data infrastructure (D2.2) and the subsequent solution pipeline.