Properly Implementing the Facade Pattern

Facade.cs

using System;

/// <summary>
/// The object which delegates to the appropriate sub-system.
/// <para>The Facade pattern is a structural pattern, whose
/// purpose is to provide a unified interface to a set of 
/// interfaces in a subsystem.</para>
/// </summary>
public class Facade
{
    #region Property(s)

    protected ISubSystemA SubSystemA { get; set; }

    protected ISubSystemB SubSystemB { get; set; }

    #endregion Property(s)

    #region Constructor(s)

    public Facade(ISubSystemA subSystemA, ISubSystemB subSystemB)
    {
        SubSystemA = subSystemA;
        SubSystemB = SubSystemB;
    }

    #endregion Constructor(s)

    #region Method(s)

    public virtual void ProcessA()
    {
        SubSystemA.Process();
    }

    public virtual void ProcessB()
    {
        SubSystemB.Process();
    }

    #endregion Method(s)
}

SubSystemA.cs

using System;

/// <summary>
/// An interface of a sub-system, which
/// we want to unify.
/// </summary>
public interface ISubSystemA
{
    void Process();
}

SubSystemB.cs

using System;

/// <summary>
/// An interface of a sub-system, which
/// we want to unify.
/// </summary>
public interface ISubSystemB
{
    void Process();
}