# SOLIOT--Decentralized Data Control and Interactions for IoT
## 6 Mapping and Interaction Model
### Data Representation
Furthermore, it outlines the existence of child resources through ldp:contains properties. It is recommended to add a property to tell the client, which kind of relation the td:Thing connects to its child. Listing 1 contains a representation of the intended Digital Twin model. Please note that despite that JSON-LD is the recommended format, the Turtle serialization has been chosen to increase the readability of the example. ```
<coap://18.157.197.66:5683/things/3S7 PMOCP4 BD>  a td:Thing, ldp:BasicContainer, saref:Device;  rdfs:label \"3S7 PMOCP4 BD\"\"xsd:string;  td:title \"3S7 PMOCP4 BD\"\"xsd:string;  td:description \"OVEL Vacuum generator\"Gen;  td:security <./.acl>;  td:actions <./affordanceCreate>, <./affordanceDelete> ;  td:events <./affordanceNotification> ;  ldp:contains <./120363/>, <./affordanceCreate>, <./affordanceNotification>, [...]. ```  
Listing 1: An IoT device presented as a SOLIOT Digital Twin. All enabled interaction possibilities (D5) are expressed also using Thing Description Affordances. In addition to the discovery of interaction patterns through the linked-data specifications using HTTP Header, the affordances bridge the gap to the non-HTTP protocol bindings. A client, unaffected by its used protocol, can thereby find the related resources, respective endpoints with protocol specifications, and lookup the necessary input and provided output details. For CoAP, the CoRE Link Format further standardizes the principles of discoverable resources in RFC 6690. These attributes are used to reflect the HTTP headers wherever possible. Domain Vocabularies (D3.2) for now are the Semantic Sensor Network (SSN/SOSA) ontology [44] and the Smart Appliances REFerence (SAREF) ontology [45]. Further descriptions of concepts and aspects originating from the description of core manufacturing, logistics, or engineering attributes shall be used from the Asset Administration Shell ontology [46] and the currently developed Industrial Ontology Foundry (IOF) [47]. Furthermore, the rich domain vocabularies maintained by eCl@ss[48] and IEC CDD (IEC 61360) define lightweight concept definitions of huge term sets using IRDIs. The currently undergoing efforts to deliver eCl@ss also through linked-data principles as RDF Resources and URI identifiers promises an even simpler integration. The security profiles (D6) are represented in the same way as proposed by SOLID. ACL files containing Web Access Control statements can be positioned at the resources and containers to describe and at the same time configure a Role-based Access Control model. A SOLIOT instance however should not rely on WebIDs, as its communication partners may not be able to prove their identity in this way. Shorter tokens, especially JSON Web Tokens with encoded claims through JSON-LD, can compose a suitable trade-off. A further restriction of data intersections is composed through SHACL shapes. These shapes serve two purposes. They directly address the need for data validation and schema restrictions (D7) but also, as readable resources themselves, describe the expected or offered data. A sending client can thereby understand the expected data structure beforehand, and even test its outgoing resources locally. A receiving client can adjust its own expectations by analyzing the shapes, and derive a better forecast of the resulting resources. The resulting virtual presentation of the Digital Twin is therefore, as shown in Listing 1, formally presented through as a 'td:Thing' as defined by the Thing Description ontology. The thereby incorporated machine-readable properties and attributes allow a client to autonomously interpret its capabilities, given that it is familiar with the vocabulary. If not, the client can also dereference the identifiers and further discover their meaning on the fly. The interaction model is further outlined through the presentation as a 'ldp:BasicContainer' and the 'td:actions' and 'td:events' attributes. These provide the client all information necessary to interact with the SOLIOT Digital Twin.