The HSQLDB license is derived from BSD-3-Clause

http://hsqldb.org/web/hsqlLicense.html
https://spdx.org/licenses/BSD-3-Clause.html

However, it's not quite the same.  It reads similar to the BSD-4-Clause, however the advertising notions are moved into the 2nd clause, and the BSD-3-Clause's 2nd clause is split into two clauses.  

John