Techniques for exchanging data are provided herein. An “open” data type is established on a computer system to define the structure of data. The open data type includes one or more predefined properties, and enables one or more extension properties to be optionally included. Data that is defined according to the open data type includes data values for the predefined properties, and may optionally include data values for extension properties. A second computer system may consider the extension properties to be extension properties or predefined properties of a data type known at the second computer system. In this manner, the type system that is used to exchange data between nodes need not necessarily be commonly known among the nodes, and/or may be dynamically modified, even for a particular data instance. Furthermore, queries may be performed against the data that query against the predefined properties and/or extension properties.