  IOP4 is a pipeline to perform photometry and polarimetry analysis of optical
data from Calar Alto (CAHA) and Sierra Nevada (OSN) observatories. IOP4
implements Object Relational Mapping (ORM) to seamlessly integrate all
information about the reduction and results in a database which can be used to
query and plot results, flag data and inspect the reduction process in an
integrated fashion with the whole pipeline. It also ships with an already
built-in web interface which can be used out of the box to browse the database
and supervise all pipeline processes. It is built to ease debugging and
inspection of data. Reduction from five different instruments are already
implemented: RoperT90, AndorT90 and DIPOL (at OSN 0.9m telescope), AndorT150
(OSN 1.5m telescope) and CAFOS (CAHA 2.2m telescope). IOP4's modular design
allows for easy integration of new observatories and instruments, and its
results have already featured in several high-impact refereed publications. In
this paper we describe the implementation and characteristics of IOP4.
