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External Libraries

The LD part of Orion-LD depends on the following external libraries:

  • microhttpd
  • libmongoc (MongoDB C driver) - requires MongoDB 4.2+
  • libcurl
  • libuuid
  • kbase
  • klog
  • kalloc
  • khash
  • kjson
  • GEOS (Geometry Engine - Open Source) - for in-memory geo-spatial subscription matching
  • librdkafka (optional, for Kafka consumer subsystem — only needed when using -kafka flag)

MongoDB Version Requirement

Orion-LD uses libmongoc (the MongoDB C driver), which requires MongoDB wire protocol version 8 or higher. This means MongoDB 4.2 or higher is required. Earlier versions (4.0, 3.6, etc.) are not supported.

The "heart" of the linked-data extension of orionld is the kjson library. kjson takes care of the parsing of incoming JSON and transforms the textual input as a tree of KjNode structs.

A KjNode tree is basically a linked list of attributes (id and type are some kind of attributes of the entity, right?) that can have children, the attribute metadata. In NGSI-LD the attribute metadata takes another name, namely Property-of-Property, or Property-of-Relationhsip, or ...

Trees based on the KjNode structure isn't just for the incoming payload, but also for:

  • outgoing payload
  • context cache
  • intermediate storage format for the DB abstaction layer
  • etc.