What is a Property Schema in Biztalk?
In Biztalk Server you have something called promoted properties which enable various Biztalk components to access important items of data from the context instead of retrieving it from the message itself. For each message type you create you can decide which data items will be used by other components in Biztalk and based on that you can promote those fields.
When you promote those required fields you may need to create an associated property schema which helps Biztalk to handle the promoted property fields. In Visual Studio you can just right click on Item that you want to promote in the Biztalk Editor and Select Promote à Quick Promotion. This will promote the field and also create a corresponding Property Schema.
Property fields or promoted properties can be accessed from various biztalk components including Pipeline and Orchestration. Property fields are also used for message routing. To be able to access the property fields data from other than Orchestration, you need to create property schema to describe the data you are promoting.
A property schema is a special schema that you associate with a message schema. It is used for promoting specific values from within an instance message into the message context. Property promotion provides a centralized mechanism for pulling key pieces of information that you define from within an instance message and making it more easily accessible to BizTalk Server components that are handling the message as it passes through BizTalk Server.
Using Quick Promotion in Visual Studio you can create promote a field and create the property Schema easily. On how to do Quick Promotion you can read here, How to Copy Data to the Message Context as Property Fields
Alternatively, you can also add a new Property Schema to your project in Visual Studio by right clicking on the Project in Solution Explorer and Select Add à New Item and Select Property Schema.
To read more on Property Schemas See Property Schemas
And to read on Different Types of Biztalk Schemas See Different Types of BizTalk Schemas