db++, made by the German company » Concept asa, is a relational database system with high performance and low memory and disk usage in mind. While providing SQL as an additional language interface, it is not really a SQL database in the first place but provides its own AQL query language which is much more influenced by the relational algebra than SQL is.
Concept asa always had an interest in supporting open source languages, db++ has had Perl and Tcl call interfaces for years now and uses Tcl as its internal stored procedure language.
This extension is EXPERIMENTAL. The behaviour of this extension—including the names of its functions and any other documentation surrounding this extension—may change without notice in a future release of PHP. This extension should be used at your own risk.