  Electronic medical data sharing between stakeholders, such as patients,
doctors, and researchers, can promote more effective medical treatment
collaboratively. These sensitive and private data should only be accessed by
authorized users. Given a total medical data, users may care about parts of
them and other unrelated information might interfere with the user interested
data search and increase the risk of exposure. Besides accessing these data,
users may want to update them and propagate to other sharing peers so that all
peers keep identical data after each update. To satisfy these requirements, in
this paper we propose a medical data sharing architecture that addresses the
permission control using smart contracts on the blockchain and splits data into
fined grained pieces shared with different peers then synchronize full data and
these pieces with bidirectional transformations. Medical data reside on each
user\'s local database and permission related data are stored on smart
contracts. Only all peers have gained the newest shared data after updates can
they start to do next operations on it, which are enforced by smart contracts.
Blockchain based immutable shared ledge enables users to trace data updates
history. This paper can provide a new perspective to view full medical data as
different slices to be shared with various peers but consistency after updates
between them are still promised, which can protect the privacy and improve data
search efficiency.
