SQLite is a small, fast, embeddable database. What makes it popular is the combination of the database engine and interface into a single library as well as the ability to store all the data in a single file. Its functionality lies between MySQL and postgresql, however it is faster than both databases.
Emdros is a text database middleware-layer aimed at storage and
retrieval of "text plus information about that text." This
information could be linguistic analyses or other annotations. Emdros
provides an abstraction of text that makes it well suited to storing
/syntactic analyses/ of text, but other linguistic information is
supported as well. Emdros comes with a query-language, MQL, that
enables powerful queries. Emdros acts as a middleware-layer between a
client (not provided) and a database back-end. Currently, postgresql,
MySQL, and SQLite (2 and 3) are supported, but other back-ends can
easily be added.