point3 *is [10 20] from time-point*4)', or temporal-causal relations like 'If (interval1 *{bef, meets}*
interval2) then (time-point3 *is [10 20] from time-point*4)' should be incorporated in these models
(Meiri, 1996). Moreover, the global consistency property introduced by Dechter (1992) is an important property in temporal networks, since it allows us to obtain solutions by backtrack-free search (Dechter, 1992; Freuder, 1982). In particular, a global consistent network would allow us to handle conjunctive queries like 'does '(interval1 {bef, meets} interval2) ∧ (time-point3 is [10 20] from time-point4*) hold?'* without propagation of the query, as it is required in (van Beek, 1991).

Stergiou and Koubarakis (1996), Jonsson and Bäckström (1996) dealt with the representation of temporal constraints by means of disjunctions of linear constraints (linear inequalities and inequations) also named Disjunctive Linear Relations (DLRs). These expressions are a unifying approach to manage disjunctive constraints on points, intervals and durations, such that these expressions subsume most of the formalism for temporal constraint reasoning (Jonsson & Bäckström, 1998). Moreover, DLRs are able to represent disjunctions of non-disjunctive metric constraints (x1y1≤c1 ∨ x2-y2≤c2 ∨ ....∨ xn-yn≤cn), where xi and yi are time points, ci real numbers and n≥1 (Stergiou
& Koubarakis, 1998). Obviously, the satisfiability problem for an arbitrary set of disjunctions of linear constraints is NP-complete. Interesting tractable subclasses of DLRs and conditions on tractability are identified in (Cohen et al., 1996; Jonsson & Bäckström, 1996; and Stergiou & Koubarakis, 1996). The two main tractable subclasses are Horn linear and Ord-Horn linear constraints (Stergiou & Koubarakis, 1996; Jonsson & Bäckström, 1998). However, these subclasses subsume temporal algebras whose management is also polynomial.

The management of a set of disjunctions of linear constraints is mainly based on general methods from linear programming, although some specific methods have been defined for tractable subclasses
(Stergiou & Koubarakis, 1998; Cohen et al., 1996; etc.). As Pujari and Sattar outline (1999), the linear programming approach, though expressive, does not take advantage of the underlying structures (e.g., domain constraints) of temporal constraints. In addition, usual concepts in temporal reasoning, as composition and intersection operations on constraints, minimal constraints, kconsistency (Freuder, 1982), decomposability (Montanari , 1974), globally consistency (Dechter, 1992), etc., and their consequences should be adapted to reasoning on disjunctive linear constraints, which is not a trivial issue.

In spite of the expressive power of the previous models, some problems (including planning, scheduling, hypothetical reasoning, etc.) also need to reason on *alternative contexts* (situations, intentions or causal projections) and to know what holds in each one of them (Dousson et al., 1993; Gerevini & Schubert, 1995; Garcia & Laborie, 1996; Srivastava & Kambhampati, 1999). This gives rise to the need to reason on context-dependent constraints. This feature is not supported in the usual temporal models in a general way, nor described in the usual expressive power of constraints
(Jeavons et al., 1999). Therefore, *ad-hoc* methods should be used when reasoning on temporal contexts is required.

These issues will be addressed in this paper. We describe a temporal model, which integrates qualitative and metric disjunctive constraints on time-points and intervals. The temporal model is based on time-points as primitive, such that intervals are represented by means of their end timepoints. However, the representation of interval constraints seems to imply some kind of relation among endpoint constraints (Gerevini & Schubert, 1995). The proposed temporal model introduces labeled constraints, where each elemental constraint (disjunct) in a disjunctive point-based metric constraint is associated to one unique label. In this way, point-based constraints can be related among