Espresso provides an API as soon as you register your database. It introspects the database schema and populates the repository with the required metadata. Each table becomes a REST endpoint with services such as pagination, filtering, and optimistic locking out-of-the-box.
HTSQL was created in 2005 to provide an XPath-like HTTP interface to PostgreSQL for client-side XSLT screens and reports. HTSQL found its audience when analysts and researchers bypassed the user interface and started to use URLs directly. The language has evolved since then.