@@ -79,6 +79,7 @@ The following referenced documents are not necessary for the application of the
-<aname="_ref_i.3">[i.3]</a> ETSI GS CIM 006: "Context Information Management (CIM); Information Model" [https://www.etsi.org/deliver/etsi_gs/CIM/001_099/006/01.03.01_60/gs_CIM006v010301p.pdf](https://www.etsi.org/deliver/etsi_gs/CIM/001_099/006/01.03.01_60/gs_CIM006v010301p.pdf)
-<aname="_ref_i.4">[i.4]</a> JSON-LD 1.1 - A JSON-based Serialization for Linked Data", W3C Recommendation 16 July 2020, [https://www.w3.org/TR/json-ld11/](https://www.w3.org/TR/json-ld11/)
-<aname="_ref_i.5">[i.5]</a> Smart Data Models [https://smartdatamodels.org/](https://smartdatamodels.org/)
-<aname="_ref_i.6">[i.6]</a> ETSI GR CIM 022: "NGSI-LD/oneM2M interworking proxy proposal" [https://www.etsi.org/deliver/etsi_gr/CIM/001_099/022/01.01.01_60/gr_CIM022v010101p.pdf](https://www.etsi.org/deliver/etsi_gr/CIM/001_099/022/01.01.01_60/gr_CIM022v010101p.pdf)
# 3 Definition of terms, symbols and abbreviations
<mark>Delete from the above heading the word(s) which is/are not applicable.</mark>
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@@ -870,6 +871,38 @@ The final question is how to anchor the NGSI-LD base resource `ngsi-ld` into the
**Figure 7.2.3-6: NGSI-LD resource as child resource of CSE Base**
## 7.3 Interworking Approaches
### 7.3.1 Motivation
oneM2M typically interfaces with existing systems defining an interworking approach. oneM2M utilizes a specialized Application Entity (AE) called Interworking Proxy Entity (IPE) to handle the interaction between the system to interwork with, using its respetive native API or reference point, and the oneM2M system, using the Mca reference point as shown in Figure 7.3.1-1.
In general, there are two types of interworking approaches - a synchronization-based approach, where the IPE is responsible for automatically synchronizing information between the two systems - and a request-based approach, where the IPE only acts when triggered by a request from one system, i.e. the information required for answering the request first needs to be gathered from the other system. Both approaches can be applied uni-directionally or bi-directionally, i.e. in one case the information is only fetched from one system an pushed to the other, but not the other way round, and in the other case this happens in both directions. Synchronization-based approaches duplicate data, but make information access more efficient, whereas request-based approach avoid any duplication of data, but answering requests becomes more expensive, possibly prohibitively expensive.
ETSI ISG CIM has already developed three synchronization-based interworking approaches <ahref="#_ref_i.6">[i.6]</a>. Two of these are uni-directional, i.e. the idea is to synchronize certain oneM2M information with an NGSI-LD system, but not the other way round, and one can be used bi-directionally, i.e. information can be fully synchronized between two systems.
These three approaches are summarized in the following. Details can be found in <ahref="#_ref_i.6">[i.6]</a>. A request-driven interworking approach is sketched as well.
As oneM2M and NGSI-LD follow different approaches, a mapping is needed. This can be a general approach, which requires a mapping language, or a specific approach which relies on a certain resource structure or a data model. The mapping information can either be stored in one (or both) of the systems or in the IPE.
### 7.3.2 IPE-driven Synchronization Approaches
**Figure 7.3.2-1: General interworking setup between a oneM2M system and an NGSI-LD Context Broker**
Figure 7.3.2-1 shows the general interworking setup between a oneM2M system and an NGSI-LD Context Broker with an IPE implementing the interworking.
Depending on the use case, oneM2M data needs synchronizing to NGSI-LD context broker or NGSI-LD data needs synchronizing to oneM2M.
* oneM2M to NGSI-LD: This can be used when services are already implemented and data are already being stored in the oneM2M platform. The goal is for users to get data of oneM2M services using the NGSI-LD API.
* NGSI-LD to oneM2M: This can be used when device management or actuation is required from NGSI-LD enabled system (e.g. city operation centre) as well as when oneM2M applications make use of NGSI-LD data.
Synchronization approaches duplicate data, but enable more efficient information access.
# 8 Mapping between the information stored in oneM2M resources and the NGSI-LD information model
<mark>Study the mapping between the information stored in oneM2M resources and the NGSI-LD information model. This includes, but is not limited to the current oneM2M semantic models (in particular SDT and the oneM2M base ontology, including SAREF integration) to the NGSI-LD information model, with the goal of making it available through an integration of NGSI-LD API and the Mca reference point. This may lead to an evolution of the current NGSI-LD and Mca, and the related information models.</mark>
