Property Schema: Property Schema Base

We use  Property Schema to promote a property (field)  so that we can access it in orchestration and use for Message routing.
Elements in property schema has different Property Schema Base value

MessageDataPropertyBase:
This is Default Schema base value of Element.
Promoted Property element which has MessageDataPropertyBase as Property Schema base can only be originated from associated Document Schema.
This kind of promoted element is limited to the Document schema.
In Orchestration, Document Schema element is associated with Promoted property Element using Promote – Show promotions (and also Quick Promotion) and than this promoted property can be used in Orchestration or Port Level.

MessageContextPropertyBase
Promoted Property element which has MessageDataPropertyBase as Property Schema base can be originated from associated Document Schema or promoted in Pipeline Components  or promoted using Correlation.
So this Property is not associated to particular Document Schema, any document schema can used this promoted property.

PartContextPropertyBase
It is like MessageContextPropertyBase but  promoted element with PartContextPropertyBase value can be used on a part of Multipart message.
For Example:
we have following Property Schema :
MessageContext element has Property Schema base as  MessageContextPropertyBase
MessageContext element has Property Schema base as PartContextPropertyBase

Following is the Multipart Message Part

So if we want to add context to the Multipart message, we can use following code
MultiPartmsg(MyBiztalk.MessageContext) //where Multipartmsg is message with MultipartMessage Type

Now, if we want to add context to a part (called Body) of Multipart message,we can use
MultiPartmsg.Body(MyBiztalk.PartContext)