Spectroscopic ellipsometry (SE) was shown to be an accurate in situ method for determining the composition and thickness of III-V semiconductor layers during growth. In order to fully exploit the potential of SE for real-time in situ control, one needs to acquire a database of optical constants. In this article, we present the acquisition and parameterization (both composition and temperature) of a fully dynamic database and its use in the real-time composition control of InAlAs grown on InP. This is accomplished by acquiring SE data from growing films of different compositions, while the temperature is controlled using feedback from band-gap thermometry. The layer compositions are assessed by fitting high-resolution x-ray diffraction patterns with a simulation based on dynamical diffraction theory. In order to improve the stability during real-time control, the database was parameterized using a transfer function model. The parameterized database was then used, in real time, during growth to control the InxAl1-xAs film composition (x) to within +/-0.003.