Make the Context Hierarchy a full Directed Acyclic Graph (DAG)

Status - Accepted

Context

Until now the context hierarchy, that is, the relationship between contexts, was a simple tree. Every context had just a single parent. While this hierarchy model applies to a lot of use cases and applications, it does not cover all of them. Recently we have had the need to use the RBAC library in a couple of projects where a simple tree was not enough, and we needed a full DAG to model the context hierarchy. The reason for that was that a given context needed to be related to more than one parent context at the same time.

Decision

1. The rbac_context table will no longer store the parent-child relationship between contexts, because that relationship now needs to be able to model a M x N type of relationship.
2. A new table, named rbac_context_parent in the database schema below, will be added to model the M x N parent-child context relationship

Consequences

• The public API functions dealing with getting, adding, updating and removing context will be changed in a BREAKING WAY.
• New public API functions will be added to be able to create and remove parent-child relationships between contexts.
• The database schema will need to be updated by the applications using the library to: ** Create the new rbac_context_parent table, ** Migrate the existing parent-child relationships from the rbac_context to the rbac_context_parent table. ** Drop the parent_id column from rbac_context table.

Notes