Military Communications and Information Technology: A Trusted ...

Chapter 1: Concepts and Solutions for Communications and Information Systems
87
The static map is supplemented with dynamic data related to current traffic
situation (cameras observing queue lengths at crossroads and sensors estimating
average speed); in future, dynamic data will also contain other important information,
as weather conditions or Insigma-specific security events and threats.
V. Graph builder
The main task of the graph builder is to construct a directed graph, containing
static (map of roads and crossroads) and dynamic (current traffic and other
dynamic data) parameters describing its edges. The complete graph is returned
in a single step: A client could influence the graph, supplying problem parameters
(including start, destination, and intermediate points), vehicle profile and some
additional options, but there is no possibility of a gradual graph construction (this
is a design decision which allows to make the interface simple). Note that graphs
for privileged and non-privileged vehicles may significantly differ.
The graph builder is responsible for graph reduction in case the routing points
are sufficiently distant. While the neighborhood of the specified points contains
a complete network of ways, more distant areas would only include main roads.
A constructed graph is equipped with a handle to data warehouse (for traffic
prediction) and needs an adapter to be configured before the graph is passed to
an optimization algorithm. This is discussed in the next section.
VI. Graph adapters
The purpose of an adapter is the calculation of weights in graph edges. The calculation
takes into account static and dynamic parameters that describe an edge
(and a way it represents). The selection of parameters and their significance depends
on a user’s request (route type, vehicle profile, etc.) and a routing algorithm. Generally,
the dispatcher (see section VIII) selects an algorithm and an adapter, which,
together, are expected to be able to solve the problem. Adapters are registered
in the server for a specified task type.
An example of a (somehow trivial) adapter could be a shortest path adapter,
which simply uses way lengths as weights values. However, more advanced adapters
would usually compose weights in a more complex way, taking into account
a number of properties. For non-additive parameters, an adapter could use a vector
of weights.
As the weights include dynamic parameters (e.g., the current traffic intensity
at a given way segment), they are functions of time. The adapter computes them
when necessary and decides on a caching strategy (for weights that are expensive
to compute, e.g., require a request to traffic data warehouse).
Note that the “physical” graph structure is not altered by an adapter. However,
in practice, the graph could be modified by weights values (e.g., a high weight value
that practically eliminates a given way at a specified time).