A partial award is immediately challengeable pursuant to Article 827, paragraph 3, of the Code of Civil Procedure only when, deciding on one or more claims, it has defined the proceedings in relation to them, having regard to the executory character which the award may assume. A non-final award, which resolves preliminary questions of procedure or of merit without defining the proceedings, is challengeable solely together with the final award.
The appointment of arbitrators by the parties has priority over the substitutive mechanism pursuant to Article 810 of the Code of Civil Procedure. In absence of specific indication on the modalities of appointment in the arbitration clause, it is correct that in the construction of the arbitral tribunal priority should be given to appointment by the parties. The substitutive mechanism of Article 810 of the Code of Civil Procedure intervenes only "in want of appointment" by the parties.
The simple circumstance that a substantive relationship is multilateral does not necessarily postulate the subsistence of necessary joinder in arbitration. Necessary joinder occurs only if the decision on such substantive relationship cannot be effective, not even among the participants in the proceedings, unless rendered in relation to all the parties to the contract.
The fact that the contract is multilateral and several parties are bound by the same arbitration agreement is not of itself sufficient to constitute necessary joinder, for which there is required the subsistence of the further requisite of impossibility of rendering a decision which is not unitary in respect of all the contracting parties.
Necessary joinder in arbitration subsists only when the action tends to the constitution or modification of a single multi-party relationship or to the performance of an indivisible obligation common to several persons. It does not occur when the tribunal proceeds, in a merely incidental manner, to ascertain a juridical situation which also concerns a third party, since the effects of such ascertainment do not extend to the latter but remain limited to the parties in the proceedings.
The ascertainment relating to the subsistence or otherwise of a situation of necessary joinder in arbitration is to be effected on the basis of the petitum, that is, on the basis of the result effectively pursued by the parties, distinguishing the effective claim from that which is adduced only for an incidental decision. Necessary joinder is configurable only in reference to the principal claims proposed by the parties, and not on what is adduced solely incidenter tantum.