Some explanations from Dave Kelsey (my personal views - recalling the history)
Section 4 - Operational Security
OS1 - What is meant by a "security model"?
Here we were considering an architecture or an agreed set of technical and managerial/policy components. In EGI for example this means - authentication is today based on an X.509 PKI with an approved set of CAs (as accredited by IGTF). Authorisation is in the hands of the VOs using VOMS attribute certificates together with a set of technical components at the service level for policy enforcement (LCAS, LCMAPS, ARGUS, etc.). We have security policies on the approved CAs, on the VO membership management procedures (registration, renewal, suspension, etc). And a top-level security policy which specifies what happens in non-compliance.
This works for eInfrastructures (or did work) because we had a single security architecture and we needed all participants and services to use it.
With the current move to different technologies, more generalised federated identity management and different levels of assurance, not forgetting new types of service like the EGI Federated Cloud service, this is no longer true.
OS1.3 - What is meant by "access control"?
"Access control" is the technical means to enforce authorisation policy and decisions. In EGI, VOMS specifies VO and sub-group membership and possession of other generalised attributes. The Access Control system then decides whether a job can be run, whether a file can be written or read based on the authorisation attributes.
to be continued