Yahoo took its second major step this year in opening up its service to the wider web, under the rubric of Y!OS (Yahoo Open Strategy, introduced here), with the release today of the Yahoo Address Book API. The first step was, as we reported in April, the SearchMonkey tools for developers and site owners to provide richer search results within Yahoo.
The Address Book API (API profile here) allows developers to both read and write contact data, with special calls to synchronize data with external address books, like that of Plaxo. Developers can access the email addresses and phone numbers of contacts, once that application has been authorized by the user. Prior to this outside developers had to ask for the Yahoo password in order to scan contacts, which had limited appeal, but now Yahoo can be the trusted Resource. By opening up its social graph in this manner, Yahoo envisions that outside developers will use the contact information for applications "such as sending invitations to seed social networks or social apps, looking up postal addresses for shipping services for online retail, and providing address "auto-complete" for messaging apps."
The calls follow a simple RESTful interface with the results returned as either XML or JSON. Developers can query the address book using any search parameters such name, area code, or category of a contact. The authorization is currently done using its proprietary BBAuth, but Yahoo promises support for OAuth, the open standard, sometime this year. Full documentation is available at the Yahoo developers' site.
As Stephen Shankland at WebWare points out, there isn't any granularity to a user's control of their social graph, but Yahoo expects to provide more classification tools in the near future.