创意设计/图案建议请求

我有许多类,它们在概念上都是相关的,但在细节层面上,有些更是如此。例如,这三个类具有几乎相同的属性(尽管成员函数会有所不同):

public class RelatedA : IRelatedType
{
    public string Name { get; set; }
    public string Value { get; set; }
    public DateTime Stamp { get; set; }
}

public class RelatedB : IRelatedType
{
    public string Name { get; set; }
    public string Value { get; set; }
    public DateTime Stamp { get; set; }
}

public class RelatedC : IRelatedType
{
    public string Name { get; set; }
    public string Value { get; set; }
    public DateTime Stamp { get; set; }
    public int Special { get; set; }
}

还有两个其他类在概念上与上述3个类相关,但在实现方面可能略有不同:

public class RelatedD : IRelatedType
{
    public string Name { get; set; }
    public string Statement { get; set; }
}

public class RelatedE : IRelatedType
{
    public string Name { get; set; }
    public string Statement { get; set; }
    public bool IsNew { get; set; }
}

这些实例可以由工厂基于某种“类型”枚举值创建。问题是,稍后在使用这些对象时(例如,在业务层中),可能会有很多这样的代码:

IRelatedType theObject = TheFactory.CreateObject(SomeEnum.SomeValue);

if (theObject is RelatedC)
{
    RelatedC cObject = theObject as RelatedC;
    specialVal = cObject.Special;
}
else if (theObject is RelatedD)
{
    RelatedD dObject = theObject as RelatedD;
    statementVal = dObject.Statement;
}
else if (theObject is RelatedE)
{
    RelatedE eObject = theObject as RelatedE;
    statementVal = eObject.Statement;
    isNewVal = eObject.IsNew;
}

这可能在许多地方重复。是否有更好的设计方法,我应该使用(必须有)?