This layer defines what is exchanged and how it is structurally and semantically described. It is organised into two sub-groupings: •Data & Data Instances Enablers: Dataset aggregates Data - the concrete data assets that flow through the exchange. Data associates with Metadata, which in turn associates with Data Mapping in the specifications group, meaning metadata is what links a raw data instance to its formal mapping rules. •Semantic Specifications Enablers: Ontology and Data Model are composed together as the core specification unit - the ontology's structure is built from (or constrains) the data model. Data Syntax aggregates into Data Model, and Data Format connects into the same composition point, meaning both syntax and format are structural constraints layered on top of the data model. Vocabulary sits in this group as the controlled-term-list specification, though it currently has no drawn relationship to the rest of the cluster - it should be read as intended to constrain the values used in Data/Metadata, but that link is not yet explicit in the model. In short: this layer answers "what does the data look like, and what rules govern its meaning and structure?" - it contains no operational or executable logic, only the descriptive/structural assets.