L6 – Logical Sequence

The L6 Logical Sequence View provides a time-ordered examination of the exchanges between participating operational nodes as a result of a particular scenario. Each event-trace diagram will have an accompanying description that defines the particular scenario or situation.

Concerns Addressed

• Operational Planning.
• User Requirements Specification.
• Service Orchestration.

Background

Operational Event-Trace Descriptions, sometimes called sequence diagrams, event scenarios or timing diagrams, allow the tracing of interactions between nodes in a scenario or critical sequence of events. The node interactions usually correspond to flows of information but may describe flows of energy, materiel or people specified in the L2, Logical Scenario.

Usage

• Analysis of operational events.
• Sequences of interactions between nodes.
• Behavioural analysis.
• Identification of non-functional user requirements.
• Operational test scenarios.

Representation

• UML sequence diagram.

Detailed View Description

The L6 View allows the tracing of interactions in a scenario or critical sequence of events and can be used by itself or in conjunction with L4, Logical Activities, and/or a L5, Logical States, to describe the dynamic behaviour of nodes in a mission or operational thread. A L6 is particularly useful for describing critical sequencing of behaviours and timing of operational activities that cannot be adequately described in L4, Logical Activities. In addition, the L6 augments the L3, Node Interactions, by outlining the sequence in which information exchanges take place between nodes.

The diagram at Figure 3-368 shows the components of a L6 view. The items across the top of the diagram are operational nodes.

Figure 3-368: L6 Schematic

Each node has a vertical lifeline associated with it. Specific points in time can be labelled running down the left-hand side of the diagram. Directed lines between the node lifelines represent interactions (e.g. information exchanges) between nodes, and the points at which they intersect the timelines represent the times at which the nodes become aware of the events.

UML sequence diagrams are appropriate for representing a L6 view. Alternatively, a L6 view may be developed using any modelling notation that supports the layout of timing and sequence of activities along with the information exchanges that occur between nodes for a given scenario. Different scenarios will be depicted by separate diagrams.

Figure 3-379: Example L6 View

If the architect is developing a service-oriented architecture, a L6 view may be used to show the sequence of interactions required to support operational activities. A “service-oriented architecture L4“ view shows which services support which operational activities. However it may be useful to show how those services are required to interact in order to support operations. Thus, a “service-oriented architecture L6” view shows lifelines for services, and the sequence of interactions between those services:

Figure 3-380: Example L6 View with Services

L6 sequences are logical sequences, specified independently of any given solution. P6, Resource Sequences, provides the solution-specific equivalent to L6, detailing the sequences that derive from the L6 for a specific Physical Architecture.

Key Elements and Their Relationships

Meta-Model

The detailed meta-model and element list for L6, Logical Sequence, is at paragraph 4.4.6.