Digital identity systems have been around for almost as long as computers and have evolved with the increased usage of online services. Digital identities have traditionally been used as a way of authenticating to the computer systems at work, or a personal online service, such as an email. Today, our physical existence has a digital counterpart that became an integral part of everyday life. Self-Sovereign Identity (SSI) is the next step in the evolution of the digital identity management systems. The blockchain technology and distributed ledgers have provided necessary building blocks and facilities, that bring us closer to the realisation of an ideal Self-Sovereign Identity. But what exactly is an ideal Self-Sovereign Identity? What are the characteristics? Trade-offs? Here, we propose the framework and methodology that can be used to evaluate, describe, and compare SSI systems. Based on our comparison criteria and the evaluation framework, we present a systematic analytical study of existing SSI systems: uPort, Sovrin, ShoCard, Civic, and Blockstack.