Knowledge4COVID-19 is a framework that aims to showcase the power of integrating disparate sources of knowledge to discover adverse drug effects caused by drug-drug interactions among COVID-19 treatments and pre-existing condition drugs. The Knowledge4COVID-19 framework is devised as a network of data ecosystems (DEs). It aligns data and metadata to describe the network and its components. Heterogeneity issues across the different data sets are overcome by various methods of data curation and integration. Each DE comprises data sets, programs for accessing, managing, and analyzing their data. Interoperability issues across a DE data sets are solved in a unified view. Mappings between the data sets and the unified schema describe the meaning of the data sets.