L2 – Logical Scenario

The L2 Logical Scenario View shows, at a high level, the interactions between logical nodes and places them in the context of location(s).

Concerns Addressed

  • User Requirements.
  • Operational Planning.
  • Scenario Specification.

Background

The L2 View specifies Nodes (elements of capability) in context of each other. The context is usually expressed in terms of the information that flows between the nodes (e.g. the information flow requirements between capabilities in a given scenario) but may also be flows of materiel, human resource or energy.

Since NAF v3.1, the L2 View has been developed to:

  • Adopt a more formal definition of logical flows to represent node connections.
  • Support the introduction of service-oriented architectures.
  • Accommodate the use of known resources (as defined in P2, Resource Structure).

Usage

  • Definition of operational concepts.
  • Elaboration of capability requirements.
  • Definition of collaboration needs.
  • Associating capability with a location.
  • Problem space definition.
  • Operational planning.
  • Supply chain analysis.

Security Usage

The L2 View can be enhanced with additional features for modelling security:

  • Security domain specification.
  • Logical entity trust models.
  • Threat specification (e.g. threat vectors) and counter-capability specifications.

Representation

  • Topological (connected shapes).
  • UML composite structure diagram.

Detailed View Description

The L2 View defines the logical structure of the architecture. The L2 takes logical nodes (elements of capability) defined in L1 Node Types and depicts Needlines between them, primarily to indicate a need to exchange or share information. The L2 may, however, also show the location (or type of location or environment) of nodes, and may optionally be annotated to show flows of people, materiel or energy between nodes. Figure 3-28 shows the Logical domains in the Search and Rescue Scenario.

Figure 3-28

Needlines document the required or actual exchange of information (or resources) between nodes; they are conduits for one or more logical flow exchanges - i.e. they represent a logical bundle of information / resource flows. There is a one-to-many relationship from needlines to logical flows (e.g. a single needline in L2 represents multiple individual logical flows). The mapping of the flows to L2 needlines occurs in the L3, Node Interactions. For example, the L2 may have a needline labelled “tasking” which represents a number of logical flows, consisting of various types of reports (information elements), and their attributes (such as periodicity and timeliness). The identity of the individual elements and their attributes are documented in L3 Node Interactions, along with the producing and consuming activities from L4, Logical Activities.

In most cases there will be only one needline between any two nodes (which may carry multiple logical flows). This is not mandatory, however, and flows may be grouped into more than one needline.

A needline does not indicate how the information transfer is implemented. L2 is not a communications link or communications network diagram but a high-level definition of the logical requirement for information exchange between elements of capability (nodes). As such, an L2 can be a powerful way of expressing the differences between an as-is architecture and a proposed architecture to non- technical stakeholders, as it can be used to emphasise how information / resource flow (or does not flow) without becoming overly-complex.

In addition to logical nodes, NAF allows known resources and operational activities to be depicted on an L2. These resources are defined in P1, Resource Types, and are to be used where a constraint on the logical solution exists due to existing resources, such as in a maritime operation where an [maritime platform] is always part of the solution.

Figure 3-289

The required locations for Nodes may also be specified. However, care must be taken when using locations. L2 is intended to be a Logical model (i.e. solution independent), and in many cases the location will not be known at design time.

Figure 3-290

L2 can also describe the trade-space by using a concept called Problem Domain. Nodes placed within the Problem Domain are those expected to be delivered in the solution. Those outside the Problem Domain are not part of the solution but represent external elements the solution will be expected to interact with. Known resources are not to be used in a Problem Domain.

Key Elements and Their Relationships

Figure

Meta-Model

The detailed meta-model and element list for L2, Logical Scenario, is at paragraph 4.4.2.