# SOLIOT--Decentralized Data Control and Interactions for IoT
## 6 Mapping and Interaction Model
### Data Representation  
SOLID's data model is oriented by the human user and its attributes, IoT devices require a different vocabulary and data scheme (cf. Table 7). The Thing Description (TD) ontology, Semantic Sensor Network (SSN) and Smart Appliances Reference (SAREF) ontology are only examples of the rich set of vocabularies and ontologies recently designed for the domain. eCl@ss and the IEC Common Data Dictionary (IEC CDD) include rich sets of non-RDF classes and attributes. While a broad range of terms and concepts is given, the actual integration between different parties and organizations requires more restrictions and selection of supported of entities. The LDP container model allows the usage of any correctly structured RDF whether the property or entity is known to the server or not. In an IoT system, the host must restrict the variety to some degree. Therefore, schemes and shapes such as SHEX or SHACL can be used to validate incoming information. Alternatively, the server can provide extended mapping capabilities and ensures the provisioning of known terms in its own authority. Nevertheless, this step, if executed autonomously, is error-prone and therefore not feasible in an operating environment. Consequently, using SOLID in an IoT environment requires additional restrictions and validation mechanisms even though this limits the expressiveness of the provided information. Using the Thing Description vocabulary (namespace prefix 'td' [43]) as the Core Vocabulary (D3.1) in combination \begin{table}
\begin{tabular}{l l l} \hline \hline  & **SOLID** & **SOLIOT MQTT/CoAP** \\ \hline Res. Identifier (D1) & HTTP(S) URL & Topic ID, CoAP URL \\ \hline Resource Locator (D2) & HTTP(S) URL & CoAP URL, TD Affordance \\ \hline Information Model (D3) & RDF, RDFS, LDP & RDF, RDFS, LDP \\ generic (D3.1) & pim/space, posix/stat & Thing Description \\ domain specific (D3.2) & DCTERMS, FOAF & SSN, SOSA, SAREF, (eCl@ss, \\  & VCARD & IOF, IEC CDD) \\ \hline Self-Description (D4) & \textless{/profile/card@me\textgreater{}} as a Person & \textless{/things/thing\#me\textgreater{}} as a Digital Twin \\ \hline Interaction Descr. (D5) & HTTP Headers (Allow, Allow-Post, & TD Affordances \\  & Allow-Patch, WAC-Allow...) & \\ \hline Security Profiles (D6) & WAC in ACL files & WAC in ACL files \\ \hline Data Schemes (D7) & – & (SHACL) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Data Representation Mapping. with the Linked Data Platform annotations, the instances of td:Thing are the top-level entities in the reserved top-level container '/things/' (cf. Figure 6). The identifying URI of such an instance must be composed of the authority of the server, '/things/', and a locally unique character sequence. The Thing is treated and described as a ldp:BasicContainer, and implements the thereby required interaction behavior. Alternatively, a relative URI only using the locally unique character sequence can be applied. The full URI of the td:Thing is the implicitly set regarding the location on the hosting server. An instance of td:Thing contains at least a minimal self-description (D4) outlining its type (class relations by _rdf:type_) and human readable annotations in English (_rdfs:label_, _rdfs:comment_) and potentially more languages. It can link to further resources using three different patterns. Datatype Properties are contained directly in the document representing the instance. Object Properties referencing external resources shall also be contained in this RDF document but limiting the provided information to the Object Property and referenced object URI. The origin server shall shift the decision to the client, whether it wants more information of that object entity. If so, the client resolves the identifier in a linked-data conform way, and discover the references resource itself. The third pattern is the reference to locally hosted resources. The instance of td:Thing acts as a ldp:BasicContainer, using relative URLs to point to the intended target.