The commissioning of the Swiss Light Source (SLS) started in Feb. 2000 with the Linac, continued in May 2000 with the booster synchrotron and by Dec. 2000 first light in the storage ring were produced. The first four beam lines had to be operational by August 2001. The thorough integration of all subsystems to the control system and a high level of automation was prerequisite to meet the tight time schedule. A careful balanced distribution of functionality into high level and low level applications allowed an optimization of short development cycles and high reliability of the applications. High level applications were implemented as CORBA based client/server applications (tcl/tk and Java based clients, C++ based servers), IDL applications using EZCA, medm/dm2k screens and tcl/tk applications using CDEV. Low level applications were mainly built as EPICS process databases, SNL state machines and customized drivers. Functionality of the high level application was encapsulated and pushed to lower levels whenever it has proven to be adequate. That enabled to reduce machine setups to a handful of physical parameters and allow the usage of standard EPICS tools for display, archiving and processing of complex physical values. High reliability and reproducibility were achieved with that approach.