In the context of a constraint-based or rule-based model, in which model entities, or nodes, are interrelated by constraints, rules, conditions or the like, addition of and changes to entity instances need to be validated against relevant constraints. A mechanism is provided for performing such validation without loading the entire configuration, which includes a set of constraints and a set of node variables. In an embodiment, an intent to modify a node is received. In response, a subset of the set of constraints is determined. The subset of constraints includes all constraints that restrict the intent to modify. Further, a subset of the set of node variables is determined. The subset of node variables includes all node variables that may have associated values that affect whether any of the subset of constraints is violated. A subset of node variable information is loaded into volatile memory. The subset of information includes only information about the subset of node variables, rather than information about all of the nodes of the model. According to one aspect, the neighborhood of nodes is dynamically extended if necessary to enact an actual requested modification to a node.