EDM4hep and podio - The event data model of the Key4hep project and its implementation

<!--HTML-->The EDM4hep project aims to design the common event data model for the Key4hep project and is generated via the podio toolkit. We present the first version of EDM4hep and discuss some of its use cases in the Key4hep project. Additionally, we discuss recent developments in podio, like the updates of the automatic code generation and also the addition of a second I/O backend based on SIO. We compare the available backends using benchmarks based on physics use cases, before we conclude with a discussion of currently ongoing work and future developments.