According to Yahoo Search Blog the newly released BOSS V2 is compatible with SQL and YQL. Following is the summery about it from the news.
BOSS + SQL, BOSS + YQL
We know that a number of BOSS developers are more familiar with SQL and YQL. We have hence upgraded our BOSS mashup to work with V2, which allows for SQL type querying for the service. As shown in this example about 15 lines of code, you can put together a complete News module. You can also use a user created YQL table with BOSS V2. Download sample mashup code or start using YQL. Your search made relational.