5.1 Motivation and key concepts

A key motivation behind the NGSI-LD API[i.2] and the underlying NGSI-LD Information Model[i.3] is to make it easy for applications to get the information they need. To achieve this, applications can specify what information they want to have. This requires a common view of the world, which is encoded in the NGSI-LD Information Model. According to the NGSI-LD Information Model, the world consist of entities. There are entities of different types that have properties and relationships to other entities. The idea is to mimic a high-level human view of the world where objects are classified by assigning names to them and putting them into relation to each other. If talking about either a Property or a Relationship, the term Attribute can be used. Both the NGSI-LD API and the NGSI-LD Information Model are specified by ETSI ISG CIM as Group Specifications.

The NGSI-LD Information Model is a meta model. There are no restrictions on what entities exist and what properties and relationships they may have. This can be specified through compatible data models, which will be further explained in clause 5.2. The NGSI-LD API itself only relies on the NGSI-LD Informtion (meta) Model and not on the specific data models, i.e. it can handle entities speficied according to any compatible data model.

Known entities can be retrieved using an identifier, whereas entities can also be discovered and retrieved in a single step using queries. Queries can be geographically scoped, i.e. entities have to be in the specified area, and filtered according to propertoes or relationships, e.g. their value has to be larger than a certain value. Furthermore, applications can subscribe to be notified regarding changes to entities or simply periodically.