be combined with information about the state of lights or the state of objects to obtain a less fine grained localization in a room/area rather than in a cell *X, Y* .

## 3.2 Model Of Health In Elderly Care

Health-related aspects of elderly care are modelled in SINDI by a two-layered graph:
the bottom layer includes what we call *indicators* and the upper layer includes what we call *items*.

The relation between items and indicators is the following: each indicator can contribute to the evaluation of one or more items when no direct evaluation of the item itself is available; while indicators do not have any mutual dependency or correlation among them, items are correlated by dependency relations indicating how a change in the value of an item may impact values of other items and how.

Details about how this graph-like structure is used in the reasoning process will be given in Section 4.

Indicators and items that are meaningful have been identified according to the medical practice in health assessment of elderly (Fleming K.C. 1995) and encoded in our declarative framework as logic facts. A reduced list of indicators evaluated by the system is provided in Table 5 while items are grouped according to the class they belong to, as described later in this section.

As one can easily understand, evaluating items is not always trivial: the incompleteness and heterogeneous nature of collected data and the need for state-based context interpretation in dynamic systems suggest that nonmonotonic reasoning techniques can be a powerful tool for effective context-dependent reasoning under the assumption of incomplete knowledge.

A careful analysis of the elderly care in home settings suggests that health-related items can be classified into four classes: State representing the well-being of the person and the environment in which she lives, Functionalities representing functional disabilities of the person monitored, Activities of Daily Living (ADLs) representing her dependence in performing daily activities, and Risk Assessment characterizing risky conditions.

In the remaining part of this section we provide details about items we consider at each level, tests and input values used for absolute evaluation and indicators that may contribute to their differential evaluation when direct input is not available.

The identification of relevant items and indicators, as well as their classification has been made possible thanks to the strict interaction with a team of clinicians in geriatrics from the "Ospedale S. Gerardo" in Monza (Milano, Italy). Under their supervision, we analyzed their protocols in elderly care and formalized our domain knowledge accordingly.

State This class of items includes:
1. comorbidity, intended as the simultaneous presence of two (or more) chronic diseases or conditions in a patient; 2. number of different classes of drugs;