This presentation will introduce a new service Tietomilli, Finnish Social Science Data Archive's new easy-to-use interface for accessing key survey data on societal participation, values and attitudes of the Finns, and changes over time. The service enables online use of the data archived at FSD without requiring statistical skills. Target user groups are schoolchildren, students, journalists, decision-makers as well as ordinary citizens. We use FSD's DDI Codebook variable level documentation that exists in XML format to combine and harmonize longitudinal datasets for Tietomilli. Access to study level documentation is also provided in the service. Reusability of FSD's DDI Codebook descriptions is enhanced by using in-house tools. We will describe the tools and how we use DDI variable level documentation to make harmonization process of survey data more affordable and less discouraging of a task. Our presentation will focus on the back-end processes and programs. We will also discuss the challenges of the project and ideas for further developments. The project is funded by the Finnish Open Science and Research Initiative and is set to come to conclusion at the end of 2016. Link to service http://www.fsd.uta.fi/suomi-monitori/.