Constraint-based Queries in a Geographical Database for Network Facilities

The path evaluation operator is one of the most important operators in a Geographical Information System. Networks are modelled with graphs (i.e., a set of labelled vertices -named nodesand a set of labelled edges). This operator is applied on huge graphs since the data set associated with a network is very important. A user's query does not involve numerous constraints (e.g., I would like to go from one place to another one). Many constraints are "implicit". This paper addresses the required database modelling to take into account these constraints. These "implicit" constraints are based on the notions of time, space and applicative units. We introduce the characterization of database alphanumeric attributes in the following classes: Neutral, Time, Space and Applicative_unit. Some aggregate functions on nodes require one to evaluate this function on a sub-set of the nodes in a path (e.g., the cost of a hotel requires spending a night in a town). We introduce the notion of transparent nodes to model irrelevant nodes for an aggregate function. We define eight classes of generic functions to model a constraint: Global Time, Local Edge Time, Local Node Time, Global Space, Local Edge Space, Local Node Space, Time-Space mixed constraints and User's specific constraints. Keyword: Geographical Information System, Query language, Network facility