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A link contract is an approach to data control in a distributed data sharing network. Link contracts are fundamental to Dataweb technology and a key feature of the XDI (XRI Data Interchange) specifications under development at OASIS (organization).
In XDI, a link contract is a machine-readable XDI document that governs the sharing of other XDI data. Unlike a conventional Web link, which is essentially a one-dimensional "string" that "pulls" a linked document into a browser, a link contract is a two-dimensional XML document that can actively control the flow of data from a publisher to a subscriber by either "push" or "pull". The flow is controlled by the terms of the contract, which can be as flexible and extensible as real-world contracts, i.e., link contracts can govern:
- Identification: Who are the parties to the contract and what data does it cover?
- Authority: Who controls the data being shared via the contract?
- Authentication: How will each party prove its identity to the other?
- Authorization: Who has what access rights and privileges to the data?
- Privacy and usage control: What uses can be made of the data and by whom?
- Synchronization: How and when will the subscriber receive updates to the data?
- Termination: What happens when the data sharing relationship is ended?
- Recourse: How will any disputes over the contract be resolved?
Like real-world contracts, link contracts can also refer to other link contracts. Using this design, the vast majority of link contracts can be very simple, referring to a very small number of more complex link contracts that have been carefully designed to reflect the requirements of common data exchange scenarios (e.g., business cards, mailing lists, e-commerce transactions, website registrations, etc.) An Identity Commons working group called Identity Rights Agreements has formed to develop the first such standardized link contracts following the model of the standardized online copyright agreements developed by Creative Commons.
Using these simple, machine-readable "chains" of link contracts can provide an interoperable solution to the complex authority, privacy, synchronization, and other data control issues that exist at a higher level than the packet layer of TCP/IP or the content transport layer of HTTP. This can be a key enabler of the emergence of the Social Web, and can also provide the underpinnings for new forms of digital rights such as Virtual Rights.