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NGSI-9/NGSI-10 information model - FIWARE Forge Wiki

NGSI-9/NGSI-10 information model

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Contents

Introduction

FI-WARE NGSI Context Management specifications are based in the NGSI Context Management specifications defined by OMA (Open Mobile Alliance). They take the form of a RESTful binding specification of the two interfaces defined in the OMA NGSI Context Management specifications, namely NGSI-9 and NGSI-10 (see FI-WARE NGSI Open RESTful API Specification (PRELIMINARY)). However, FI-WARE NGSI Context Management specifications will not implement those parts of the OMA specs that prove to be useless or unnecessarily complex. Besides, they solve some ambiguities in the OMA specs and extend them when necessary to implement the FI-WARE Vision.

Change history

Revision Date Changes Summary
July 14, 2012
  • 1st stable version
May 12, 2014
  • Updated link to OMA document
  • Removed some duplicate information
  • Fixed some typos

Basic NGSI Context Management Information Model

Entities

The central aspect of the NGSI-9/10 information model is the concept of entities. Entities are the virtual representation of all kinds of physical objects in the real world. Examples for physical entities are tables, rooms, or persons. Virtual entities have an identifier and a type. For example, a virtual entity representing a person named “John” could have the identifier “John” and the type “person”.

Attributes

Any available information about physical entities is expressed in the form of attributes of virtual entities. Attributes have a name and a type as well. For example, the body temperature of John would be represented as an attribute having the name “body_temperature” and the type “temperature”. Values of such attributes are contained by value containers. This kind of container does not only consist of the actual attribute value, but also contains a set of metadata. Metadata is data about data; in in our body temperature example this metadata could represent the time of measurement, the measurement unit, and other information about the attribute value.

Attribute Domains

There also is a concept of attribute domains in OMA NGSI 9/10. An attribute domain logically groups together a set of attributes. For example, the attribute domain "health_status" could comprise of the attributes "body_temperature" and "blood_pressure".

Context Elements

The data structure used for exchanging information about entities is context element. A context element contains information about multiple attributes of one entity. The domain of these attributes can also be specified inside the context element; in this case all provided attribute values have to belong to that domain.

Formally, a context element contains the following information

  • an entity id and type
  • a list of triplets <attribute name, attribute type, attribute value> holding information about attributes of the entity
  • (optionally) the name of an attribute domain
  • (optionally) a list of triplets <metadata name, metadata type, metadata value> that apply to all attribute values of the given domain

NGSI Context Management Interfaces

OMA NGSI defines two interfaces for exchanging information based on the information model. The interface OMA NGSI-10 is used for exchanging information about entities and their attribute, i.e., attribute values and metadata. The interface OMA NGSI-9 is used for availability information about entities and their attributes. Here, instead of exchanging attribute values, information about which provider can provide certain attribute values is exchanged.

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