TIXI is a fast and simple XML interface library for applications written in C, C++, Fortran, Java, and Python. Although simplified and somewhat restricted compared to a fully-fledged XML processing library, it can create documents, create and delete nodes, and add and remove element attributes. Routines for reading and writing text nodes and nodes holding integer and floating point numbers are included, along with routines that process aggregates of these simple types for the processing of geometric data, multidimensional arrays, or arrays of vectors.
lib4d_sql is a C library that provides the required functions (connect, prepare, execute, etc.) for writing an SQL client for 4D databases. It uses the public 4D SQL protocol, which is supported by 4D products since version 11. It is already used by the PDO_4D Open Source project, and it might be used to provide others drivers for JDBC, ADO, or ActiveRecord.