This chapter explores the effect that changing access patterns has on the performance of database management systems. Changes in access patterns play an important role in determining the efficiency of key performance optimization techniques, such as dynamic clustering, prefetching, and buffer replacement. However, all existing benchmarks or evaluation frameworks produce static access patterns in which objects are always accessed in the same order repeatedly. Hence, we have proposed the dynamic evaluation framework (DEF) that simulates access pattern changes using configurable styles of change. DEF has been designed to be open and fully extensible (e.g., new access pattern change models can also be added easily). In this chapter, we instantiate DEF into the dynamic object evaluation framework (DoEF), which is designed for object databases, that is, object-oriented or object-relational databases such as multimedia databases or most eXtensible Mark-up Language (XML) databases.